vol47 03 review

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ndian J Physiol Phar ma col 2003; 47 (3) : 247269

C o r r e s p o n d i n g A u t h o r

REVIEW ARTICLE

NE UROP HYSIOLOGY OF PAIN : INSIGHT TO OROFACIAL PAIN

O. P. TANDON*, V. MALHOTRA*, S. TANDON** AND I. DSILVA

*Depar tm ent of Phys iology,

Un iversity College of Medical Sciences & Gu ru Teg Bah adu r Hospita l,

Di lsha d Gar den , Delh i 110 095

a n d

**Depar tm en t of Pe r iodon t i a ,

Na i r Hospi ta l Denta l Col lege ,

Mumbai 400 008

((((( R e c e i v e d o n J a n u a r y 2 2 , 2 0 0 3R e c e i v e d o n J a n u a r y 2 2 , 2 0 0 3R e c e i v e d o n J a n u a r y 2 2 , 2 0 0 3R e c e i v e d o n J a n u a r y 2 2 , 2 0 0 3R e c e i v e d o n J a n u a r y 2 2 , 2 0 0 3 )))))

Ab s t r a ct :Ab s t r a c t :Ab s t r a ct :Ab s t r a c t :Abs t r ac t : T h i s i s a ve ry exc it ing t ime in t he f i e ld o f pa in re sea rch . Ma jor

advances a re made a t eve ry l eve l o f ana lys i s f rom deve lopment to neura l

p l a s t i ci t y i n t h e a d u l t a n d f r om t h e t r a n s d u ct i on o f a n ox io u s s t i m u l u s i n

a pr imar y afferent neur on t o the impact of th is s t imu lus on cor t ica l c ircui t ry .

The molecular ident i t y of nociceptors , th e i r s t im ulus t ra nsdu ct ion pr ocesses

a n d t h e i o n c h a n n e l s i n v o l v e d i n t h e g e n e r a t i o n , m o d u l a t i o n a n d

propaga t ion o f act ion po ten t i a l s a long the axons in which th ese nocicep to rs

a r e p r e s e n t a r e b e in g v i g or o u s l y p e r u s e d . S i m i la r l y t r e m e n d o u s p r og r e s s

has occur red in the iden t i f i ca t ion o f the recep to rs , t r ansmi t t e r s , s econd

m e s s e n g e r s y s t e m s , t r a n s c r i p t i o n f a c t o r s , a n d s i g n a l i n g m o l e c u l e sun de r ly ing th e neur a l p la s t i c ity obse rved in the sp ina l co rd and b ra ins tem

af te r t i s sue o r ne rve in ju ry . Wi th recen t in s igh t in to the pha rmaco logy o f

d i ffe ren t neur a l c i rcu i t s , t he imp or t ance o f descend ing m odu la t o ry sys tems

i n t h e r e s p o n s e o f t h e n e r v o u s s y s t e m t o p e r s i s t e n t p a i n a f t e r i n j u r y i s

be ing r eeva lua t ed . F ina l ly, imag ing s tud ie s r evea led th a t in form a t ion abou t

t i s s u e d a m a g e i s d i s t r i b u t e d a t m u l t i p l e f o r e b r a i n s i t e s i n v o l v e d i n

a t t en t iona l , mot iva t iona l , and cogn i t ive a spec t s o f the pa in expe r ience .

K e y w o r d s :K e y w o r d s :K e y w o r d s :K e y w o r d s :K e y w or d s : pa in pa t h wa ys eva lu a t ion p a in r e l ie f

or ofa cia l p a in evok ed p ot en t ia ls TSE Ps

INTRODUCTION

P a i n : t h e I n t e r n a t i on a l p e r s p e ct i v eP a i n : t h e I n t e r n a t i on a l p e r s p e c t i veP a i n : t h e I n t e r n a t i on a l p e r s p e ct i v eP a i n : t h e I n t e r n a t i on a l p e r s p e c t i veP a i n : t h e I n t e r n a t i on a l p e r s p e c t i ve

A C om m i t t e e o f t h e I n t e r n a t i on a l

Associat ion for t he s t ud y of pa in h as d efin

pa in as an u npleasan t sensory and emot io

experience associated with a ctu al or poten

t i ssu e dam age (1). I t i s mos t ly accompa n

by the des i r e t o s top and to avo id s t im

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248 Tan don et a l In dian J Ph ysiol P ha rma col 2003; 4

caus ing i t . I t i s l i nked wi th a f ee l ing o f

avers ion (2) . Throughout most of recorded

h i s t o r y , p a i n w a s c h a r a c t e r i s e d a s a n

e ffe ct i v e fe e l i n g s t a t e r a t h e r t h a n a

sensa t ion (3). Em ot ions p lay a key ro le in

pa in fu l exper ience . Ar is t ot le descr ibed pa in

as a pas s ion o f sou l , d i s t i nc t f rom theclassic f ive senses (4) .

Melzack and Wal l (5) and Melzack a

Ca sey (6) developed a m odel of pa in in wh

t i s s u e d a m a g e con c u r r e n t l y a c t i va

sens ory, discr imina t ive, cognit ive-evalu at

and a f f ec t ive -mot iva t iona l componen t s

pa in .

S u b s t r a t e s o f p a i n : n e u r o a n a t o m y of pS u b s t r a t e s o f p a i n : n e u r o a n a t o m y of pS u b s t r a t e s o f p a i n : n e u r o a n a t o m y of pS u b s t r a t e s o f p a i n : n e u r o a n a t o m y of pS u b s t r a t e s o f p a i n : n e u r o a n a t o m y of p

p a t h w a y sp a t h w a y sp a t h w a y sp a t h w a y sp a t h w a y s

Receptors of pa in

Sensory receptors for pa in , noc icepto

a r e n a k e d n e r v e e n d i n g s t h a t t e r m i n a t e

th e sk in an d mos t o the r t i s sues of t h e bo

However , the i r d i s t r ibut ion i s not uni foth roughout orga ns of th e body. As a gene

ru le , deep v iscera l organs of the body

not wel l suppl ied wi th nociceptors . Th

receptors a re genera l ly c lass i f ied accord

to the type to wh ich they r e spond :

1 . M ech a n o se n s it i ve p a i n r e ce p t or s r e s p o

to mecha n ica l da ma ge .

2 . T h er m os en s it i ve p a i n r e ce pt or s r e s po

to r e spond to t empera tu re ex t r emes .

3 . Chemosens it i ve pa in r ecep tor s r e spond

c h e m i c a l s t h a t o c c u r w i t h d a m a g

t i s s u e s e x a m p l e h y p e r t o n i c s a l i

p o t a s s i u m c h l o r i d e , a c e t y l c h o l i

5 -H y d r o xy t r y p t a m i n e , h i s t a m i

b radyk in in a nd subs t a nce P . Vasoactamines a re r e l eased ju s t a f t e r i n ju ry

th e basoph i l s , p l a t e l e t s an d ma s t ce l

As these r ecep to r s s igna l e i the r ac t

o r p o t e n t i a l d a m a g e t o t i s s u e s , p a i n

sur vival value to the organism. Consequen

p a i n r e c e p t o r s g e n e r a l l y d o n o t a d a p t

F i g. 1 : P a t h w a y by wh i ch F a s t P a i n is con v ey ed t o

t h e C e n t r a l N e r v o u s .

I VI : L a m i n a e of t h e D or s a l H o r n of t h e

Spinal Cord.

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In d ia n J Ph ysiol P h a r m a col 2003; 47(3) Neurophysiology of Pain : Insight of Orofacia l Pain

e v i d e n c e f o r t h e e x i s t e n c e o f c u t a n e o

mye l ina t ed A and unmye l ina t ed C f ib

was p rov ided by Zo t t e rmann (8 -10) , w

i n t e r p r e t e d h i s o b s e r v a t i o n s a s s t r o

suppor t fo r Be l l s and Mul l e r s t heo ry

specif ici ty (11,12) . I t is known that noxio

s t imu la t ion exci t i ng soma t i c and den ta la f fe ren t s ma y exe r t a ma sk ing or i nh ib it

e f fec t on C-f iber re la ted sensa t ions . Tab

I to I I I desc r ibe the pe r iphe ra l mechan i

and r ecen t deve lopmen t s i n ion channe

n e u r a l t r a n s m i s s i o n a n d t r a n s d u c t i o n

pa in sensa t ion .

M o le c u l e s i n v ol v e d i n p a i n t r a n s m i s s i onM o le c u l e s i n v ol v e d i n p a i n t r a n s m i s s i o nM o le c u l e s i n v ol v e d i n p a i n t r a n s m i s s i onM o le c u l e s i n v ol v e d i n p a i n t r a n s m i s s i o nM o le c u l e s i n v ol v e d i n p a i n t r a n s m i s s i o n

The ro le of t r ophic fac tors an d cytoki

in th e developmen t a nd m ain t ena nce of p

in r esponse to var ious form s of t i s su e in j

i s a n a r e a o f r e s e a r c h t h a t h a s v i r t u a

exp loded in t he l a s t s eve ra l yea r s .

In addi t ion to i t s ro le in developme

NGF an d o ther growth fac tors , an d cytoki

h a v e b e e n s h o w n t o m e d i a t e p a i n ahype ra lges ia a s socia t ed wi th t i s sue in ju r

Lorne Mendel l (20) the f i r s t to descr

t h e l in k b e t w ee n N G F m e ch a n i s

under ly ing the in i t ia l hypera lges ic respo

to NGF. The in i t ia l hypera lges ia in r espo

t o s y s t e m i c o r p e r i p h e r a l l y a d m i n i s t e

N G F d e p e n d s o n i n d i r e c t m e c h a n i s m

specifica l ly ma s t ce l l degra nu la t ion .

Linda Watkins (21) descr ibed addi t io

pa thways th rough which ac t iva t ion o f

i m m u n e s ys t e m r e s u l t s i n ch a n g e s

m u l t i p l e s i t e s t h r o u g h o u t t h e n e r v o

sys t em. Watk ins desc r ibed the molecu

involved in the s igna l ing pa thways as w

prolonged s t imu lat ion. In fact pain sen sat ion

may in t ens i fy a s pa in th re sho lds become

lowered through cont inued s t imula t ion (7) .

F r o m t h e p e r i p h e r a l r e c e p t o r t o t h ecerebra l cor t ex , specia l i sed neur a l pa th ways

t e r m e d t h e n o c i c e p t i v e s y s t e m p r o c e s s

n o x i o u s s t i m u l i . P e r i p h e r a l l y , n o x i o u s

s t i m u l i a c t i v a t e s p e c i f i c r e c e p t o r s

(nociceptors) of thinly myelinated A a n d

unmye l ina t ed C f ibe r s t e rmina t ing in the

spina l cord dorsa l h orn . Neu rophys iologica l

F i g. 2 : P a t h w a y b y w h i ch s low pa i n is con v e ye d t o

t h e C e n t r a l N e r v o u s S y s t e m .

THALAMUS

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T AB L E I I : R e ce n t d e ve lop m e n t s on I on ch a n n e ls & n o ci ce p t i on i n t h e p er i p h e r a l n e r ve .

S .N o. S ci e n t i s t /R e s e a r ch e r Wor k

1 . S t ev e Wa xm a n (1 3 ) I n d ica t ed D y n a m ic ch an ge s of e xp r e s s i on of T T X-s e n s i t ive s odc h a n n e l c o n t r i b u t i n g t o h y p e r e x c i t a b l e n o c i c e p t o r s a f t e r i n j u r y

2 . Mich a e l Gold (14) Role of Mod u la t ion of TTX-r es is t a n t s od iu m cu r r en t s by P GE 2, 5a n d a d e n o s i n e m o d i f i e s m e c h a n i c a l i n d u c e d h y p e r a l g e s i a d u ri n f l a m m a t i o n .

3 . Da n ie l We in r ech (1 5 ) Role of Ca++

d e p e n d e n t K+

cur ren t in con t ro l l ing exc i tab i l i ty o f va f f e r e n t s .

4 . P et er M cN a u gh t on (1 6 ) P r e s en t e d e v i d e n ce im p l i ca t i n g a ct iva t ion of P r ot ei n Ki n a s e ha c t i v a t e d c h a n n e l b y b r a d y k i n i n

Note : These mechan isms exp la in the ion ic bas i s o f inc rease in hyperexc i tab i l i ty in p resence o f noc icep t

T AB LE I : C h a r a ct e r is t ics of fa s t a n d s l ow fi be r s (7 ).

F a s t (Dia gr a m 1) S low (D ia gr a m 2 )

Carried by A By C fibers

Sh a r p, pr ick in g sen sa t ion Du ll, a ch in g, bu r n in g

Ea sily loca lised P oor ly loca lised

Occu r s fir s t Occur s second; persist for longer t ime, m or e u nplea

Occurs on s t imulat ion of mechanical and thermal receptors Occurs on s t imu lat ion of polymodal receptors

T AB L E I I I : T r a n s d u c t ion t r a n s m i s s ion a n d m od u l a t i on of n o ci ce p t i ve in f or m a t i on .

S .N o. S ci e n t i s t /R e s e a r ch e r Wor k

1 . Am y Ma c Der m ot t (17) E xp er im en t s on t he r ole of p r es yn a p t ic n on -N MDA & k ain a t e r ecepin dorsa l roo t gang l ion neurons . Ac t iva t ion o f these recep tors appt o i n f l u e n c e g l u t a m a t e r e l e a s e f r o m t h e s e n s o r y n e u r o n & t h e r ea c t i v a t i o n o f d o r s a l h o r n n e u r o n s .

2 . E dw in McC le s k ey (1 7 ) U sin g E le ct r op hys iology, s in gle -ce l l P CR a n d r eve r se t r a n s cr ipP C R r e a c t i o n s d e t e r m i n e d t h e n u m b e r o f m R N A c o p i e s e n c o d i n g- o p i o d r e c e p t o r i n a s i n g l e c e l l . T h e i r r e s u l t s e x p l a i n e d p e r p l e xaspec ts o f op iod ana lges ia .

3 . Mich ae l S a l t e r (18) P rovid e d e vid e n ce-s u pp or t in g d eve lop m en t of lon g-t er m p ot en t iai n t h e h i p p o c a m p u s a n d b y a n a l o g y , c e n t r a l s e n s i t i s a t i o n o f s pc o r d d o r s a l h o r n n e u r o n s a f t e r t i s s u e i n j u r y .

4 . E d wa r d P er l (19) P oin t ed ch a n ges in - a d r e n e r g i c r e c e p t o r s p r e s e n t i n s e n s o r y n e u ra f t e r i n j u r y . E x p r e s s i o n o f t h e r e c e p t o r s i n v o l v e d i n t r a n s m i s s i o nn o c i c e p t i v e s t i m u l i c o n t r i b u t e s p a t h o p h y s i o l o g y o f p a i n .

Note : Researchers on recep tors invo lv ing the t ransduc t ion , t r ansmiss ion , and modula t ion o f noc icepi n f o r m a t i o n i s c l e a r l y o n e o f t h e m o s t e x c i t i n g a n d r a p i d l y a d v a n c i n g i n v o l v e d i n t h e t r a n s m i s s i o nn o c i c e p t i v e s t i m u l i a s w e l l a s t h e c e l l u l a r e l e m e n t s n e c e s s a r y f o r s y n a p t i c t r a n s m i s s i o n . R e s e a r c hh a v e b e g u n t o c o l l e c t t o g e t h e r t h e e s s e n t i a l e l e m e n t s f o r t h e f i r s t s t e p s u l t i m a t e l y l e a d i n g t o p e r c e p t i o n o f p a i n .

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as how ac t iva t ion of th i s sys tem resul t s in

changes in behavior .

S t e v e M c M o h a n ( 2 2 ) s u m m a r i s e d t h e

growing body of da ta impl ica t ing a c r i t ica l

ro le for br a in der ived neu rot r ophic fac tor in

the a l te red nocicept ive process ing observed

in t he p re sence of in f lam ma t ion .

Brain derived n eurotrophic factor appear s

t o fu n c t i on a s a n e u r o t r a n s m i t t e r /

Neuromodu la to r i n the do r sa l ho rn o f t he

spina l cord , where i t i s re leased f rom the

cent ra l te rminals of smal l -ca l iber a f fe rents

an d increases t he exci ta b i l ity of dorsa l horn

n e u r o n s .

S p i n a l i n t e g r a t i n g m e ch a n i s m o f p a i nS p i n a l i n t e g r a t i n g m e ch a n i s m o f p a i nS p i n a l i n t e g r a t i n g m e ch a n i s m o f p a i nS p i n a l i n t e g r a t i n g m e ch a n i s m o f p a i nS p i n a l i n t e g r a t i n g m e ch a n i s m o f p a i n

From the pa in r ecep to r s , pa in impu l ses

ar e car r ied to the CNS by two fiber sys tems:

th e lar ge myelinat ed f ibres (A-del ta ) conduct

impulses rap id ly (15 .25 m/sec) , the smal l

unmyel ina ted f ibres (C-f ibres ) conduct a t a

s lower rate (

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C on s e q u e n t l y , n a t u r a l l y occu r r i

(En dogenous) opia t e compoun ds wer e fou

These compounds are col lect ively cal led

E n d o r p h i n s . T h r e e - e n d o r p h i n c o m p o u n

met (meth ionine) enkephal ine , leu ( leuc i

encepha l in and be ta endorph ins a re kno

to p l ay a ro l e i n na tu ra l pa in suppres smechanisms. These a re pr oduced a t d i ffe r

l e v e l s o f C N S a s a r e s u l t o f p a i n

s t i m u l a t i o n . T h e y s e r v e t o r a i s e p

th re sho ld and r educe pa in .

P h a n t o m l i m b a n d p l a s t i c i t yP h a n t o m l i m b a n d p l a s t i c i t yP h a n t o m l i m b a n d p l a s t i c i t yP h a n t o m l i m b a n d p l a s t i c i t yP h a n t o m l i m b a n d p l a s t i c i t y

Amputat ion of l imb is of ten fol lowed

the f ee l ing tha t l imb i s s t i l l p r e sen t . Tphenomenon i s t e rmed a s pha n t om l imb a

e n h a n c e s ou r u n d e r s t a n d i n g of p a

p a t h w a y s . T h e p h a n t o m a r e a g r a d u a

sh r inks a nd m ay comple t e ly d i sappea r . B

in 5 to 10% am put ees ; t h e re i s a pe r s i s t

an d seve re pa in appa ren t ly from the abs

region . The pa in i s thought to be of cent

o r i g i n . O n s e c t i o n i n g o f c o n t r a l a t e

sp ino tha lamic t r ac t s pa in may be r e l i evfor long periods by a prolonged or sev

s t imulus to the s tump; a l though in o th

t h e s t u m p m a y b e r e a m p u t a t e d

anaes the t i s ed wi thou t any r e l i e f .

Fool ing the bra in may re l ieve pa in

mi r r or i s app l ied in be tween the am pu t a

l imb and the no rma l l imb . The pa t i en t

a sked to look in the mi r ro r and move

norm al l imb. Visua l s t imu l i of movement

norma l l imb make the ind iv idua l f ee l a

h i s ampu ta t ed l imb i s mov ing . Th i s b r in

back a surge of p las t ic i ty changes in

c o r t e x , w h i c h a r e l i n k e d t o s u r g e

emotiona l cha nges th at rel ieve th e limb fr

i t s l o c k e d p o s i t i o n a t t h e t i m e

am put a t ion (7).

e l imina ted fear , anxie ty and suf fer ing . The

op ia t e r ecep to r s a r e pa r t o f t he na tu ra l ly

o c c u r r i n g o r e n d o g e n o u s , a n a l g e s i c

m e ch a n i sm w i t h i n t h e h u m a n n e r v ou s

system . Ana lgesics rel ieve pain an d th e most

p ot e n t a n a l ge s i c i s t h e m or p h i n e . I t

complexes wi th opia te receptors assoc ia tedwi th synap t i c t e rmina l s o f t he subs t an t i a l

g e l a t i n os a a n d t h e g r a y m a t t e r t h a t

su r rounds the th i rd ven t r i c l e o f t he b ra in

s tem (per iaqueducta l gray) . Morphine when

complexed wi th opia t e r eceptors , r educes or

e l imina te s pa in .

W i t h d i s c o v e r y o f o p i a t e r e c e p t o r s ,

came a s ea rch fo r t he i r na tu ra l func t ion .

F i g. 3 : E n d og en ou s P a in R el ie f S ys t e m .

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i n c r e a s e d r i g i d i t y g u a r d i n g h e l p s

loca l i s ing the poss ib l e sou rce o f pa in

p a r t i c u l a r v i s c e r a . G a l l b l a d d e r p a i n

re fe r r ed to r igh t shou lde r t i p and ca rd

pa in to l e f t shou lde r and uppe r a rm. Su

re fe r r ed pa in thus he lps in mak ing co r r

d iagnos is of the d iseased v iscera .

S u b c or t i ca l m e c h a n i s m sS u b c or t i ca l m e c h a n i s m sS u b c or t i ca l m e c h a n i s m sS u b c or t i ca l m e c h a n i s m sS u b c or t i ca l m e c h a n i s m s

Pi tu i t a ry mecha n i sms

Melzack R. pos tu la t ed t he ex is ten ce o

pain n eur oma tr ix in which t he exper ienc

pain i s pr oduced by mu l t ip le inf luences a

c o m p r i s e s o f a w i d e l y d i s t r i b u t e d n e unet work wi t h inpu t f rom the bodys s t r e

r egu la t ion sys t ems , i nc lud ing H ypoth a lam

Pi tu i t a ry ax i s (HPA) and op io id sys t em

Fa cia l pa in i t se l f ma y act , on t he o ther h a

as a s t rong ac t iva tor of the HPA. (25)

C e r e b r a l c or t i ca l m e ch a n i s m sC e r e b r a l c or t i c a l m e c h a n i s m sC e r e b r a l c or t i ca l m e ch a n i s m sC e r e b r a l c or t i c a l m e c h a n i s m sC e r e b r a l c or t i c a l m e c h a n i s m s

The cur ren t kn owledge of pain percepti s qui te fra gment ar y . The ro le p layed by

c e r e b r a l c o r t e x i n p a i n i s n o t c l e a

u n d e r s t o od . I f t h e p o s t c e n t r a l g yr

( s o m a t o s e n s o r y a r e a ) i s e l e c t r i c a

s t i m u l a t e d , v e r y f e w p a t i e n t s r e p o r

sensa t ion of pa in . The cor tex i s thought

a i d i n t h e a p p r e c i a t i o n o f p a i n , b u t

r e sponses to pa in fu l s t imu l i pe r s i s t ev

when the cor tex i s surg ica l ly removed

g r e a t d e a l o f e v i d e n c e i m p l i c a t e s

t ha l amus in the pe rcep t ion o f pa in .

N e w e r c on c e p t s o f u n d e r s t a n d i n g c or tN e w e r c on c e p t s o f u n d e r s t a n d i n g co r tN e w e r c on c e p t s o f u n d e r s t a n d i n g c or tN e w e r c on c e p t s o f u n d e r s t a n d i n g co r tN e w e r c on c e p t s o f u n d e r s t a n d i n g co r t

m e c h a n i s m sm e c h a n i s m sm e c h a n i s m sm e c h a n i s m sm e c h a n i s m s

A c o n s i d e r a b l e a m o u n t o f e v i d e n

sugges t t ha t P r ima ry Soma tosensory cor

Mar ie F i tzgera ld (23) repor ted changes

i n t h e n e o n a t a l s p i n a l cor d t h a t a r e

incomple te vers ions of what occurs in the

adu l t . Cen t r a l s ens i t i s a t ion occur s i n the

re sponse to e l ec t r i ca l s t imu la t ion o f A

f ibers whereas ac t iv i ty induced p las t ic i ty

in th e adu l t sp ina l cord t akes p l ace on ly inr e s p o n s e t o C f i b e r s t r e n g t h s t i m u l a t i n g

un less the dorsa l h orn i s pr imed by previous

p e r i p h e r a l i n j u r y . N M D A r e c e p t o r s a r e

d i st r ibu ted in h ighe r dens i ty in th e neona t a l

cord.

C l i f f o r d W o o l f ( 2 4 ) p r o v i d e d a n

outs tanding , concise and up to da te rev iew

o f a c t i v i t y - i n d u c e d a n d s i g n a l i n d u c e dp la s t i c i ty in s enso ry neurons a f t e r t i s sue

in jury .

R e f e r r e d p a i n : I t s s i g n i f i c a n c eR e fe r r e d p a i n : I t s s i g n i f i ca n c eR e f e r r e d p a i n : I t s s i g n i f i c a n c eR e fe r r e d p a i n : I t s s i g n i f i ca n c eR e fe r r e d p a i n : I t s s i g n i f i ca n c e

T h e p a i n o r i g i n a t i n g f r o m v i s c e r a i s

gene ra l ly o f s low, ach ing type , wh ich i s

diff icul t to local ise . Frequ ent ly visceral pa in

may be r e fe r r ed to o the r pa r t s o f t he body

s u p p l i e d b y t h e s a m e s p i n a l n e r v e ( t h ede rma tomal ru l e ) known as r e fe r r ed pa in .

When pa in i s r e fe r r ed t o an oth e r pa r t o f t h e

body, the s i te of re fer r a l i s usu a l ly a pa r t of

t h e b o d y t h a t d e v e l o p s f r o m t h e s a m e

embryologica l segment or d erma tome, as t he

a f f e c t e d s o u r c e o f t h e p a i n . T h e s a m e

p e r i p h e r a l n e r v e s s u p p l y t h e s e c o m m o n

regions of the body. For example , the hear t

a n d a r m a r e d e r i v e d fr o m t h e s a m ed e r m a t o m e , a n d t h e k i d n e y , u r e t e r a n d

te s t e s a r e a l l de r ived from a no the r comm on

d e r m a t o m e .

Clinical s ignif ican ce of clas sical referr ed

pain l ies in d ia gnos is . Usu al ly v iscera l pa in

o f t h e a b d o m e n m a y c a u s e o v e r l y i n g ,

a b d o m i n a l m u s c le s t o con t r a c t . T h i s

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(S I ) h a s a p i v ot a l r o le i n s e n s o r y

discr imina t ive aspects of pain su ch a s spat ial

discr imin at ion (26) and int ensi ty coding (27).

Cogni t ive fac tors can a l t e r t he per ce ived

i n t e n s i t y o f p a i n a n d a c c o r d i n g l y , c a n

modula te SI ac t iv i ty in func t iona l imaging

s t u d i e s . P h y s i o l o g i c a l l y , i n h i b i t i o n o f

n o c i c e p t i v e n e u r o n s a n d n e u r o n s w i t h

n o n s e n s o r y d i s c r i m i n a t i v e r e s p o n s e

c h a r a c t e r i s t i c s m a y b e i n v o l v e d i n t h i s

cogni t ive modula t ion and in in te rac t ion of

p a i n a n d t ou c h in S I a r e a .

Neu rophysiologic an d fun ct iona l ima ging

da ta c l ea r ly ind ica t e pa r t i c ipa t ion o f S I Ii n h u m a n p a i n p r o c e s s i n g . P r e s e r v e d ,

d i r e c t t h a l a m i c a c c e s s o f n o c i c e p t i v e

in fo rma t ion to S I I , suppor t ed by ana tomic

tha lamocor t ica l connect ions and by para l le l

a c t i v a t i o n o f s o m a t o s e n s o r y c o r t i c e s ,

sugges t s a pa r t i cu la r r e l evan ce of t h i s a r ea

in pa in process ing .

F u n c t i o n a l l y , S I I m a y b e i n v o l v e d i nrecogni t ion , lear n in g an d mem ory of pa in fu l

event s (26,28-32)

N u m e r o u s f u n c t i o n a l i m a g i n g s t u d i e s

i n d i c a t e p a r t i c i p a t i o n o f a n t e r i o r i n s u l a r

co r t ex in human pa in p roces s ing . Recen t

f i n d i n g s i n d i c a t e a d e d i c a t e d p a i n a n d

t e m p e r a t u r e p a t h w a y t o t h e i n s u l a n e e d t o

be in t eg ra t ed wi th fun ct iona l ima g ing da t a .

Funct iona l ly the insula may be involved in

au tomat i c r eac t ions to nox ious s t imu l i and

in pain -relat ed memory an d learn ing (33-35).

C l in i ca l r e p or t s t h a t p a t i e n t s w i t h

c ingulo tomies somet imes s t i l l fee l pa in but

r e p o r t i t a s l e s s d i s t r e s s i n g a l o n g w i t h

f indings tha t h igh leve l of opio id b inding

o c c u r s i n t h e A n t e r i o r c i n g u l a t e c o r

(ACC). Pa in a f fec t ( i . e . unpleasantness

pa in) i s encoded in the ACC.

By us ing hypnos is , Rainvi l le e t a l (

select ively al ter ed un pleasa nt ness of noxi

t h e r m a l s t i m u l i w i t h ou t ch a n g in g t

perce ived pa in in tens i ty .

Ana lysis of cerebr al act ivat ion pa t t ern

m e a s u r e d b y P E T r e ve a l ed t h a t t

modula t ion of pa in a f fec t was para l le led

ac t iva t ion changes in the ACC but not

t h e o t h e r b r a i n t i s s u e s .

Along wi th these and o the r s tud ie s p r o x i m i t y o f t h e n o c i c e p t i v e , m o t o r a

c o g n i t i v e r e g i o n s o f t h e A C C s u g g e

p o s s i b l e l o c a l i n t e r c o n n e c t i o n s t h a t m

a l low the ou tpu t o f t he ACC pa in a rea

c o m m a n d i m m e d i a t e b e h a v i o r a l r e a c t i o

(37-40)

G r a d i n g / E v a l u a t i o n of p a i nG r a d i n g / E v a l u a t i o n of p a i nG r a d i n g / E v a l u a t i o n of p a i nG r a d i n g / E v a l u a t i o n of p a i nG r a d i n g / E v a l u a t i o n of p a i n

P a i n i s a c o m p l e x p h y s i o l o g i c

behav io ra l puzz le tha t r equ i r e s a s ses sm

on different levels .

At t he same t ime the measu res o f p

should be re l iab le an d va l id , oth er wise th

w i l l b e o f l i t t l e u s e t o c l i n i c i a n s

resea rchers (41). An idea l pa in m easu re (

shou ld p rov ide sens i t i ve measu remen t fof bias , pr ovide imm ediat e inform at ion a b

accur acy an d r e l i ab il it y . The measu rem

s h o u l d a l s o s e p a r a t e t h e s e n s o

d i s c r i m i n a t i v e a s p e c t s o f p a i n f r o m

hedon ic qua l i t i e s a s ses s expe r imen ta l a

cl inical pain wit h t he sa me scale and pr ov

absolute scales tha t a l low assessm ent of p

be tween groups an d wi th in groups over t im

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The pa in th re sho ld can be de t e rmined

by the c lass ica l methods . S imple ca tegory

s c a l e s s u c h A s f o u r - p o i n t n o n e , m i l d ,

modera t e and seve re (ve rba l ca t egor i ca l

scale) or 1-10 numerical scale can be scored

in seve ra l ways . The s imples t , t he me thod

of eq u a l a p p e a r i n g in t e r v a l s a s s i g n ss u c c e s s i v e i n t e g e r s t o v e r b a l c a t e g o r i e s

d i r e c t l y ( 4 3 ) . T h e t h r e e m o s t f r e q u e n t l y

cons idered aspec ts of pa in a re th e su bject ive

(Measured by se l f - r epor t ) , t he behav io ra l

(measured by sampling of physiological or

e lec t r ic potent ia l s and assaying body f lu ids

or o ther b io logica l responses . ) Se l f - repor t

measu res , when t hey can be obta ined , should

be regard ed as t he Gold s ta nda rd. Indeed ,the In t e rna t iona l Assoc ia t ion fo r t he s tudy

o f p a i n e m p h a s i s e s t h a t p a i n i s a l w a y s

subject ive.

F o r t u n a t e l y , t e c h n i q u e s for t h e

psychological a ssessmen t of the pa in pa t ient s

ha ve impr oved to the ex ten t t ha t emot iona l

s t r e s s s u c h a s a n x i e t y , d e p r e s s i o n a n d

d e f e n s i v e p e r s o n a l i t y s t y l e s c a n n o w b e

ident ified. People experien cing pain a re able

t o r e p o r t s e p a r a t e l y o n t h e s e n s o r y a n d

affect ive dimensions and emotional qual i t ies

d i ffe r d ra ma t ica l ly across d i f fe ren t form s of

c l in i ca l pa in and wi th in ind iv idua l s ove r

t i m e ( 4 4 ) . C u r r e n t l y e v i d e n c e i n d i c a t e s

t h a t p h a r m a c e u t i c a l a n d p s y c h o l o g i c a l

in t e rvent ions h ave d i ffe ren t e f fects on e th er

sensory , a f fec t ive or both qual i t ies of the

exper ience .

S u b j e ct i v e p a i n a s s e s s m e n tS u b j e ct i v e p a i n a s s e s s m e n tS u b j e ct i v e p a i n a s s e s s m e n tS u b j e ct i v e p a i n a s s e s s m e n tS u b j e ct i v e p a i n a s s e s s m e n t

A Visu al Ana logue S cale (VAS) is a sim ple

measure of subjec t ive pa in . I t cons is t s of a

10-cm hor izonta l or ver t ica l l ine wi th two

end p oint s labeled no pain an d worst p ain

ever.

The sub jec t i s r equ i r ed to p l ace a m

o n t h e 1 0 -c m l in e a t a p o in t , w h

corresponds to the leve l of pa in in tens

the subjec t present ly fee ls . The d is tance

cm f rom the lower end of the VAS to

p a t i e n t s m a r k i s u s e d a s a n u m e r i ca l i n

of the severi ty of pain. (45,46)

The VAS is s ens i t ive to pha rm acologi

a n d n o n - p h a r m a c o l o g i c a l p r o c e d u r e s t

a l t e r t h e e x p e r i e n c e o f p a i n ( 4 7 ) a

c o r r e l a t e s h i g h l y w i t h p a i n m e a s u r e d

verba l and numer ica l ra t ing sca les (48 ,4

The ease o f adm in i s t r a t ion a nd scor ing h

cont r ibut ed to the popular i ty of th i s meth

A ma jor a dvan t age of t h e VAS as a measuof sensory pa in in tens i ty i s i t s ra t io sc

p rope r t i e s (50 ) , min ima l i n t rus iveness a

concept ua l s imp lici ty (51).

The t r ad i t i ona l v i ew tha t t he ce reb

cor t ex i s not involved in pa in pr ocess ing h

been abandoned during th e past decade ba

on an at omic an d ph ysiologic s tu dies , les io

s t u d i e s , fu n c t i on a l n e u r oi m a g i n g aneurophys io logic s tudies in humans .

The use o f t echn iques such a s mic

reco rd ings o f t he un i t a ry o r mul t iun i t

ac t iv i ty of th e nerves or nuc le i, in t ra cran

e v o k e d p o t e n t i a l s , n o c i c e p t i v e e v o k

poten tia ls, reflexology, polysomn ogra ph y a

topograph y toge ther wi th techniques such

percutaneous object ive local isat ion of d

ne rves , a l l ows quan t i t a t ive eva lua t ion p

in t ra and pos topera t ive ly (52) .

E v o k e d P o t e n t i a l sE v ok e d P o t e n t i a l sE v o k e d P o t e n t i a l sE v ok e d P o t e n t i a l sE v o k ed P o t e n t i a l s

Speci f ic s t imula t ion a t per iphery cau

nerve impulses to be conveyed to the br

s e n s o r y a r e a s p r o d u c i n g a t t h e c e r e b

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cor tex an e lec t r ica l potent ia l change ca l led

th e Cort ical Evoked Response. This potent ial

c h a n g e c a n n o t b e r e c o r d e d a s a s i n g l e

response because i t i s too smal l to show up

a g a i n s t t h e n o r m a l v a r i a b i l i t y of t h e

electroencephalogram (EEG). However, i f a

cons ide rab le number ( s ay 50 o r more ) o f evoked r e sponses a re p r oduced a nd th e EE G

tr acings ar e ana lysed by a sui t able compu ter ,

th e average response becomes a ppar ent a fte r

due am pl i fica t ion .

E v ok e d p o t e n t i a l s a r e a com p l e x

s u m m a t i o n o f g r a d e d p o t e n t i a l s a l o n g

a f f e r e n t p a t h w a y s a n d a t t h e c o r t e x b y

peripheral vol leys. (53)

I t i s t e m p t i n g t o r e g a r d t h i s e v o k e d

po ten t i a l r e sponse a s an ind ica to r t ha t t he

neura l impu l ses in i t i a t ed by the s t imu lus

ha ve r eached consc iousn ess , and t ha t i t i s a

phys ica l i nd ica to r o f pe rcep t ion , bu t two

fac tors a re not necessar i ly co inc ident . (54)

P a i n a n d co gn i t i onP a i n a n d co gn i t i onP a i n a n d co gn i t i onP a i n a n d co gn i t i onP a i n a n d co gn i t i on

E v e n t R e l a t e d P o t e n t i a l s ( E R P ) a r e

va luable and usefu l para meters for a ssess ing

a v a r i e t y o f c o g n i t i v e a b i l i t i e s ( 5 5 ) a n d

psychological pr ocesses including expecta ncy,

a t ten t ion , search , d iscr im ina t ion , decis ion

mak ing and memory . P 300 i s a va luab le

too l and ou r p re l imina ry work have shown

t h a t i t c a n e v a l u a t e t h e c o g n i t i v e a n d

affect ive componen ts of pa in (56-59)

A s igni f icant increase in P 300 la tency

in pa t en t s su f fe r ing from pa in a s compa red

to age an d sex ma tched cont ro ls . Our finding

sugges t t ha t t he re a re cogn i t ive cha nges in

chronic pa in s ta tes . This cogni t ive b lunt ing

i s r eve r s ib l e wi th ana lges i c i n t e rven t i

(60) . Cont ingent Negat ive Var ia t ion (CN

i s a s u r f a c e n e g a t i v e s l o w p o t e n t

recorded f rom hu ma n subjects dur ing a f i

foreper iod of a warned reac t ion t ime ta

(61).

The e lec t r ica l phenomenon of the bra

h a s d r a w n t h e i n t e r e s t o f m a

psychophysiologis ts because i t ref lects so

psychological processes such as expectan

mot iva t e a t t en t ion and a rousa l . The C

waveform depen ds pr ima rily on ps ychologi

an d to a lesser ex ten t on ph ys ica l pr opor t

o f t he s t imu lus .

C N V ca n b e u s e d t o e va l u a t e t

affect ive-emotiona l comp onen ts of pain. I

sti l l unclear h ow bra in processes emotiona

a n d p a i n , a n d w h a t a r e t h e i n t e r a c t i

mechan i sms o f emot ion and pa in .

S low b ra in po ten t i a l s i n t he con t ing

negat ive var ia t ion (CNV) are found to

l a rge r i n the pa in cond i t ion th an th a t of cont r o l (62-64). When pa t ien t s wi th chr o

pain were s tu died in The CNV par adigm,

a p p e a r a n c e o f C N V r e s p o n s e w a s m

marked. I t was concluded tha t s low evok

poten t i a l s a r e s ens i t i ve to anx ie ty l evel a

to pain percept ion. Rizzo (65) have sho

t h e u s e f u l n e s s o f t h i s m e a s u r e i n

invest igat ion of pain a s a complex sensa t i

A number o f r ecen t s tud ie s have a s ses

the inf luence of base l ine or induced mo

on subject ive an d psychological r esponses

exper imen t a l s t imu la t ion . Base l ine (66) a

induced (67 ) anx ie ty have been shown

increase pa in r a t ings to th e rma l or p re s s

p a i n r a t i n g s , w h i l e a n e x p e r i m e n t a

i n d u c e d d e p r e s s i v e m o o d ( i n d u c e d

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s t i m u l u s i n t e n s i t y a n d p a i n f u l n e s s a

in i t ia t ion of motor movements .

Fur the r ana lys i s by Chen e t a l (70 )

the cons is tency and re l iab i l i ty of the pa

r e l a t e d s o u r c e s r e v e a l e d t h a t t w o p

re la t ed componen ts a re cons is t en t ly foun

negat iv i ty a t 145 msec . and a pos i t iv i ty

225 msec . The in i t ia l components cor re l

wi th s t imu lus in t ens i ty and appea r t o co

in fo rma t ion abou t i n t ens i ty o f t he ex te r

s t i m u l a t i o n . T h e l a t t e r c o m p o n e n t s

c lose ly re la ted to the subjec t ive es t imat

o f p a i n i n t e n s i t y a n d s e e m t o r e f l

ass oc ia t ion processes involved in eva lua t

of noxious s t imulus .

Chen e t a l fi nd ings sugges t t h a t t h e l

componen ts of the E P wa veform m ay r efl

t h e c o g n i t i v e a s p e c t s o f d e n t a l p

percept ion in labora tory models .

W h e n a n a l g e s ic i n t e r v e n t i on s a

i n t r o d u c e d s u b j e c t i v e r e p o r t s o f p a

i n t e n s i t y i s r e d u c e d a n d E P c o m p o n ediminish accordingly.

Ze lansky e t a l (71 ) sugges t ed tha t

pa in EP r eflects t he emot iona l -mot iva t io

r e s p o n s e t o p a i n r a t h e r t h a n t h e s e n s o

discr imin at ive componen ts .

S o m a t o s e n s o r y e v ok e d p o t e n t i a l sS o m a t o s e n s o r y e v ok e d p o t e n t i a l sS o m a t o s e n s o r y e v ok e d p o t e n t i a l sS o m a t o s e n s o r y e v ok e d p o t e n t i a l sS o m a t o s e n s o r y e v ok e d p o t e n t i a l s

Fol lowing s t imula t ion of sensory recepto

a ser ies of e lec t r ica l events ensues in

a f fe r e n t p a t h w a y a n d i n t h e b r a i n , a n d t

a c t i v i t y m a y b e m e a s u r e d n o n - i n v a s i v

f r o m s i t e s o n t h e b o d y s u r f a c e . T

waveform is kn own a Soma tosensory E vok

Po ten t i a l .

present a t ion of tex t wi th depr ess ive them es)

decrea sed t olera nce to cold pr essor pa in (68).

P a i n m e m o r y p r o ce s s e s h a v e b e en

i n v e s t i g a t e d u s i n g e x p e r i m e n t a l p a i n f u l

s t i m u l a t i o n ( 6 9 ) . T h e s e s t u d i e s p r o v i d e

experiment al exam ples of how th e experience

of chronic pa in can exer t subt le inf luenceon cogni t ive pr ocesses a nd mood. Pa in i t se l f

can a l so impai r cogni t ive and psychomotor

per formance .

P a i n e v ok e d p o t e n t i a l sP a i n e v ok e d p o t e n t i a l sP a i n e v ok e d p o t e n t i a l sP a i n e v ok e d p o t e n t i a l sP a i n e v ok e d p o t e n t i a l s

Evoked Po ten t i a l s (EP s ) a r e s t imu lus o r

e v e n t r e l a t e d e l e c t r i c a l s i g n a l s o f b r a i n

ac t iv ity th a t ma y be recorded f rom th e sca lpwhen prec ise ly cont ro l led d iscre te s t imul i

a re de l ivered .

Significan t corr elation exists bet ween lat e

EP components by exper iment a l pa in s t imul i

and the induced pa in sensa t ion .

EP s can serve as indica t ors of percept ion

a t m u l t i p l e l e v e l s . P a i n r e l a t e d b r a i n

e v o k e d p o t e n t i a l s a r e r e c o g n i s e d a s a n

object ive and qu an ti t a t ive test for evalua t ion

of periphera l and cent ra l spinotha lamic t r act ,

t h a l a m o c o r t i c a l p r o j e c t i o n s a n d c o r t i c o -

cort ical c ircui t for pain processing.

Chen e t a l (70 ) i den t i f i ed the cu r ren t

s o u r c e d i p o l e s i n n o x i o u s i n f o r m a t i o n

processing.

The pa in r e l a t ed componen t s l a t e and

u l t r a l a t e a r e d i s t r ibu ted b i la t e ra l ly in both

hemisphe res exh ibi t ma x imu m am pl itu de in

th e ver t ex. Th l a t e componen t s a r e a s su med

t o r e f l e c t s e c o n d a r y m e c h a n i s m s o f

i n f o r m a t i o n p r o c e s s i n g , s u c h a s s t i m u l u s

r e c o g n i t i o n , l o c a l i s a t i o n , e s t i m a t i o n o f

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The eva lu a t ion of soma tosensory evoked

po ten t i a l s i s ma in ly r e l a t ed to a s ses smen t

o f a p a r t i c u l a r n e r v e t o c e n t r a l n e r v o u s

sys t em pa thway .

Resul t s in our s tu dies ha ve demonst ra ted

t h a t t h e r e i s a c h a n g e in t h e a b s ol u t e p e a k

la ten cy of N19 in pa t ien t s wi th chr onic pa in .

I m a g i n g : MR I a n d S P E C TI m a g i n g : MR I a n d S P E C TI m a g i n g : MR I a n d S P E C TI m a g i n g : MR I a n d S P E C TI m a g i n g : MR I a n d S P E C T

D u r i n g t h e l a s t d e c a d e , a d v a n c e s i n

fun ct ional brain im aging techniques ha ve led

to ident ificat ion of neu roan at omic subst ra tes

o f pa in pe rcep t ion . Human l e s ion s tud ie s

u s i n g c o m p u t e r t o m o g r a p h y a n d M R I ,a n d fu n ct i on a l n e u r oi m a g i n g s t u d i e s

u s i n g S i n g l e - P h o t o n E m i s s i o n C o m p u t e d

T o m o g r a p h y ( S P E C T ) , p o s i t r o n e m i s s i o n

tomogra phy (PET) an d fun ct iona l ly ( fMRI).

Ken Casey (72) described the role of for

b r a i n m e c h a n i s m s o f p a i n i n i m a g i n g i n

humans and reviewed convinc ing evidence

th at th e perceived intensi ty of un i lat eral pa inevoked by d i ffe ren t inp ut as cor r e la t es wi th

increases in regional cerebral blood f low in

p r ima r i ly five s t r uc tu r e s . B il a t e ra l ly in th e

t h a l a m u s , t h e c o n t r a l a t e r a l i n s u l a , t h e

b i la t e ra l p r emoto r cor t ex , t h e con t r a l a t e ra l

an te r io r c ingu la t e and ce reb ra l ve rmis .

T h e c o m b i n e d u s e o f p s y c h o s o c i a l

d imens ion and imag ing in humans shou ldhelp revea l the funct iona l ro le of d i f fe rent

fo r e b r a i n s t r u c t u r e s t h a t h a v e d i r e ct

c o r t i c o f u g a l p r o j e c t i o n s t o t h e t h a l a m u s ,

b ra in s t em, and sp ina l co rd , and the reby

modulat e the pa in experience at t hose levels .

These studies non-invasively dem onst ra ted

involvement of d is t r ibut ed cerebr a l a r eas in

hu ma n pa in process ing involves a var ie ty

s u b c o r t i c a l a n d c o r t i c a l r e g i o n s . M

r e c e n t l y , t o p o g r a p h i c a s p e c t s o f p a

rep resen ta t ions in the ce reb ra l co r t ex ha

been ex tended to the t empora l domain

r e su l t s o f neu rophys io log ic s tud ie s us

whole sca lp magnetoencephlography (MEan d EE G (73).

Thus i t m ay be conc luded th a t pa in i

persona l , subject ive experience inf luenced

cu l t u r a l le a r n i n g , t h e m e a n i n g of t

s i tua t ion , a t ten t ion and o ther psychologi

va r i ab le s . Approaches to measu remen t

pa in inc lude verba l a nd n um er i c s e l f-r a t

s ca l e s , behav io ra l obse rva t ion sca l e s aph ysiological res ponses. The complex nat

o f t h e e x p e r i e n c e o f p a i n s u g g e s t s t

measu remen t s f rom these domains may

a l w a y s s h o w h i g h c o n c o r d a n c e . F u r t h

d e v e l op m e n t a n d r e f i n e m e n t of p

measu rement techn iques wil l be ab le to m

t h e c h a l l e n g e a n d l e a d t o i n c r e a s i n

accur at e t ools with great er predict ive powe

O r o fa c i a l a n d d e n t a l p a i nO r o fa c i a l a n d d e n t a l p a i nO r o fa c i a l a n d d e n t a l p a i nO r o fa c i a l a n d d e n t a l p a i nO r o fa c i a l a n d d e n t a l p a i n

In t roduct ion t o den t a l pa in

Face i s cons idered as a mir ror of mi

I n w a r d e v e n t s , e m o t i o n s , b e h a v i o r s

ref lected on facial expressions. The cor

i s a l s o a m i r r o r i m a g e t o t h e b od y .

re f lec ts the body image and perce ives w

t h e b o d y e x p e r i e n c e s . T h e c o r t i

h o m u n c u l u s o f t h e b o d y h a s w i d

repr esenta t ion for orofacial a rea as compa

to o ther par t s . This i s e luc ida ted be low

deta i l a long wi th th e c lin ica l s igni f ican c

When a pa t i en t comes to the den t i s t a

compla ins of pa in , th e dent i s t i s not dea l

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with a s imple sensory phen omen on involving

t h e p e r i p h e r a l n e u r a l e v e n t s e l i c i t e d b y

p a i n f u l s t i m u l i . P a i n i n d e n t i s t r y h a s a

s e n s o r y d i s c r i m i n a t i v e d i m e n s i o n . I t

p r o v i d e s i n f o r m a t i o n a b o u t t h e n o x i o u s

s t imul i - cha rac t e r i s ed by qua l i t y , i n t ens i ty ,

l o c a t i o n a n d d u r a t i o n , p a i n f r o m o t h e rreg ions may no t r e f l ec t t ha t , where

P a i n h a s m u l t i d i m e n s i o n a l e m p h a s i s ,

involves a ffective, motiva tiona l an d cognit ive

components . In orofac ia l pa in for example

th e pa t i en t s l a s t v i s i t t o t he den t i s t , and

ongoing sensory exper iences of s t ress and

a n x i e t y d u r i n g t h e cu r r e n t v i s i t m a y

modula te the pa in exper ience . (73 ,74) .

Sensory d is tur bances of the face and ora l

cavi ty can occur in nu mber of s i tua t ions th a t

a re o f pa r t i cu la r i n t e re s t t o t he o ra l and

maxi l lofac ia l surgeon. These inc lude nerve

les ions du r in g removal of ma ndibu lar cys ts ,

t h i r d m o l a r s , o s t e o t o m i e s o f t h e f a c i a l

ske leton a nd ma x il lofac ia l t r a um a .

Temporo Mand ibu la r Di so rde r s (TMD)compr ise by fa r the most common cause of

chr onic fac ia l pa in condi t ions wi th a h igher

prevalence in women as compared to men

( 7 5 ) . T M D a r e a c o m p l e x h e t e r o g e n e o u s

group of condit ions, involving mast icatory

musc le s and / o r t emporomand ibu la r j o in t s ,

c h a r a t e r i s e d b y c h r o n i c f a c i a l p a i n a n d

r e p r e s e n t i n g c a u s e o f p h y s i ca l a n d

psychologica l d ebi li ty in a la r ge segment of populat ion.

A cc om p a n i m e n t s o f p a i nA c c o m p a n i m e n t s o f p a i nA cc om p a n i m e n t s o f p a i nA c c o m p a n i m e n t s o f p a i nA c c o m p a n i m e n t s o f p a i n

Sensory-d iscr imin a t ive sys tem (76)

U n d e r o r d i n a r y c o n d i t i o n s , a n o x i o u s

st im ulu s can quickly be local ised in t im e an d

p l a c e . S o m a t o s e n s o r y a n d d o r s o l a t e

s p i n a l c o r d a r e s o o r g a n i s e d t h a t t

s p a t i ot e m p o r a l i n f or m a t i on i s r a p i

t r ansmi t t ed . The do r sa l co lumn nuc leus

t o p o g r a p h i c a l l y o r g a n i s e d s o t h a t c e

r e s p o n d i n g t o s t i m u l a t i o n f r o m a s m

a r e a o f t h e b o d y a r e c l u s t e r e d t o g e t ha n d a r e p h y s i ca l l y a d ja c e n t t o t

neu r ons th a t r eceive inpu t from con t iguo

a r e a s o f t h e b o d y . T h i s s y s t e m a l l o

ident i fica t ion of pa in d ur a t ion a nd i t s ex

locat ion.

A seconda ry input in to the pos tero la t e

and ven t r a l pos t e ro l a t e ra l t ha l amic nuc

i s f rom d i r ec t sp ino tha lamic t r ac t i npu tm e a n s o f f i b r e s t h a t a s ce n d i n t

ven t ro l a t e ra l sp ina l co rd - the c l a s s i c p

pa t hway . These r a p id ly condu ct ing n euro

form an a l te rn a t e pa th way for d iscr imina t

somatosensory funct ions .

M o t i v a t i o n a l - a f fe c t i v e s y s t e m ( 7 6 )M o t i v a t i o n a l - a f f e c t i v e s y s t e m ( 7 6 )M o t i v a t i o n a l - a f fe c t i v e s y s t e m ( 7 6 )M o t i v a t i o n a l - a f f e c t i v e s y s t e m ( 7 6 )M o t i v a t i o n a l - a f fe c t i v e s y s t e m ( 7 6 )

The pa leo sp inotha lamic sys tem cons is t sf i b e r s o f t h e v e n t r o l a t e r a l s y s t e m t

synapse in the r e t i cu la r fo rma t ion o f

b ra in s t em, where neu rons fo rm a comp

n e t w o r k w i t h e x t e n s i v e c o n n e c t i o n s

ascend ing and descend ing sys t ems .

Th i s complex sys t em may p rov ide

n e u r a l p a t h w a y s for t h e a v e r s i

motivat ional component of pain-the suffer

a s p e c t s o f t e n a s s o c i a t e d w i t h p a i n

exper iences . In a ddi t ion t o in t e ra ct ions w

th e limbic sys tem an d the h ypoth a lam us ,

s y s t e m p r o j e c t s t o p e r i a q u e d u c t a l g

ma t t e r , where i t i n t e rac t s wi th descend

i m p u l s es t h a t u l t i m a t e l y a i d i n t

modu la t ion of impu l se t r an smis s ion wi t

th e sp ina l cord .

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M a n y d r u g s , p a r t i cu l a r l y n a r c ot i c

a n a l g e s ics , ca n a l t e r t h e a v e r s i v e -

mot iva t iona l aspec ts of th e pa in exper ien ce .

That i s , th ese agent s reduce fear a nd a nxiety

a n d c a n e l i m i n a t e t h e s u f f e r i n g a s p e c t s

associated with pain . Indifferen ce to noxious

s t i m u l u s i s b r o u g h t a b o u t i n t h i s m a n n e r .P a t i e n t s m a y s t a t e t h a t t h e p a i n h a s n o t

decreased in in tens i ty but th ey are n o longer

both ered by i t . Drugs creat e th is indifferen ce

to pa in .

A ct i v a t i on o f m o t o r m e c h a n i s m s ( 7 6 )A ct i v a t i on o f m o t o r m e c h a n i s m s ( 7 6 )A ct i v a t i on o f m o t o r m e c h a n i s m s ( 7 6 )A ct i v a t i on o f m o t o r m e c h a n i s m s ( 7 6 )A ct i v a t i on o f m o t o r m e c h a n i s m s ( 7 6 )

Motor m echa n i sms t ha t a r e r e spons ibl e for

m a n y o f t h e o v e r t r e a c t i o n s t o p a i n a r ein t e r r e l a t ed wi th spa t io - t empora l ana lys i s

and af fec t ive aspec ts of the exper ience of

p a i n . O n c e i n t e g r a t e d w i t h i n t h e c e n t r a l

n e r v o u s s y s t e m , t h e i m p u l s e t r i g g e r s a

sequence of responses charac ter i sed in the

individua l by:

1) S t ar t le r es pon s e

2) F le xion r e sp on s e

3) P os t u ra l re ad ju s tm en t

4) Voca lis a t ion

5) O r ie n t a t ion of t h e h e a d a n d eye s t o

e xa m i n e t h e d a m a g e d a r e a ,

6) E v oca t i on o f p a s t e x p er i e n ce i n s i m il a r

s i tua t ions ,

7) P r e d i ct i on o f t h e c on s e q u e n ce of t h es t imu la t ion , and

8) M a n y ot h e r p a t t e r n s of b eh a v ior a i m e d

a t d imin i sh ing the sensory a nd a f fect ive

components of the en t i re exper ience .

Fac ia l g r imac ing , c l ench ing the t ee th ,

c r y i n g a n d o t h e r m a n i f e s t a t i o n s o f t h e

e x p e r i e n c e m a y o c c u r . C h a n g e i n v i

s igns may a lso occur . Sympathe t ic nerv

sys t em func t ion i s gene ra l ly enhanced

well .

Thus the pa in cen te r , a s pos tu l a t ed

th e spec ifici ty th eory , ha s been r eplaced

th e encompa ssing global concept of an act

sys tem. The sys tem is not only respons i

for ident if icat ion, appreciat ion, recognit i

and r eac t ion t o the unp leasan t nes s impu l

a r r iv ing f rom the pe r iphe ry , bu t i t i s a

in t imate ly involved wi th the modula t ion

i m p u l s e t r a n s m i s s i o n a t s p i n a l c o r d

t r igeminal nuc leus) leve ls .

H o w d i ffe r e n t i s t h i s p a i n f r o m g e n eH o w d i ff e r e n t i s t h i s p a i n f r o m g e n eH o w d i ffe r e n t i s t h i s p a i n f r o m g e n eH o w d i ff e r e n t i s t h i s p a i n f r o m g e n eH o w d i ffe r e n t i s t h i s p a i n f r o m g e n e

p a i n ? : p e c u l i a r i t i e s o f d e n t a l p a i np a i n ? : p e c u l i a r i t i e s o f d e n t a l p a i np a i n ? : p e c u l i a r i t i e s o f d e n t a l p a i np a i n ? : p e c u l i a r i t i e s o f d e n t a l p a i np a i n ? : p e c u l i a r i t i e s o f d e n t a l p a i n

T h e t o o t h p u l p h a s m a n y a t t r a c t

f ea tu re s fo r t he s tudy o f pe r iphe ra l p

mechanisms because of i t s r ich innerva t i

i t s un ique d i s t r ibu t ion o f ne rve f ibe r s a

i t s genera l d i spos i t ion to g ive r i se to p

upon s t imula t ion (76-84). In th e last centu

t h r e e t h e or i e s e x p la i n i n g t h e e x

m e c h a n i s m o f s e n s i t i v i t y o f d e n t i n , t

s e e m i n g l y i n e r t s t r u c t u r e h a s b e

e luc ida ted:

1 . P a i n i s a d ir e ct r e s u l t of s t im u l a t ion

sensory ne rve end ings in th e den t in . T

mos t s ens i t i ve a r ea o f t h e t i s sue i s n

the den toenamel junc t ion .

2 . O d on t ob la s t s a r e s e n s or y ce ll s. T h

r e c e i v e a n d t r a n s f e r s t i m u l i t o n e

end ings in the pu lp .

3 . H y d r od yn a m i c t h e or y : D en t a l s e n s it i v

i s a resu l t o f mechanica l s t imula t ion

free end ings in th e pu lp cau sed by r a

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f lu id f low in the den ta l t ubu le s where

t h e d e n t i n i s s t i m u l a t e d .

Orofac i a l pa in can be a s s eve re a s any

p a i n e x p e r i e n c e d a n d i n c l u d e s c a s e s o f

i n t r a c t a b l e p a i n a s w e l l a s a c u t e p a i n .

Moreover personal , family and social cost of

t h i s i s e n o r m o u s , n o t j u s t i n t e r m s o f

finan cia l l os s an d cos t of t r ea t men t bu t a l so

i n t h e r i s k o f d r u g a d d i c t i o n , m u l t i p l e

opera t ions and even su ic ide . These fea tures

a r e p e c u l i a r t o o r o f a c i a l p a i n . T h e m o s t

f requent source of orofac ia l pa in i s denta l

d i s o r d e r s a n d i t h a s b e e n e s t i m a t e d t h a t

toothache is suffered for upto f ive mil l ion

days , and one mi l l ion n ights s leep los t as aresu l t of i t , in one year , in Br i ta in a lone

(85) . This a r t ic le he lps the reader develop

h i s u n d e r s t a n d i n g o f o r o f a c i a l p a i n i n

par t icu lar , wi th an objec t of explor ing the

n e w e r t e c h n i q u e s a n d p r o c e d u r e s t h a t

i m p r o v e h i s d i a g n o s t i c a b i l i t y f o r b e t t e r

t r e a t m e n t .

P s y c h o l o g y o f d e n t a l p a i nP s y c h o l o g y o f d e n t a l p a i nP s y c h o l o g y o f d e n t a l p a i nP s y c h o l o g y o f d e n t a l p a i nP s y c h o l og y o f d e n t a l p a i n

P e r h a p s t h e m os t i m p o r t a n t fa c t or

affect in g rea ct ion t o pa in is bas ic emotion of

fear . A pa in in t he leg might wel l el ici t l ess

of a r eac t ion t ha n a pa in o f equa l i n t en s i ty

in the ches t becau se the l a t t e r migh t appea r

to the su fferer t o s igni fy hear t d i seas e . Pa in

in the head ( inc lud ing the f ace ) a r e a l so

rega rded wi th g rea t e r apprehens ion s ince

they migh t a ppea r t o th rea t en the inne rmos t

being includin g mind an d th ough t pr ocessing

in th e cor t ex. Pa in d is tor t s th i s norm al inner

image caus ing a fee l ing of revuls ion . The

c l i n i c i a n a t t e m p t s t o s e e t h i s p i c t u r e t o

determ ine its a t t r ibutes , cha ra cter is t ics . This

a r t i cl e in fu r t he r i s a s t ep in t h i s d i r ect ion

an alysing n ewer m eth ods of electr oph ysiology

to un de r s t a nd th i s b lu r r ed image in o r

t o i m p r o v e t h e d i a g n o s t i c a b i l i t y a

t r e a t m e n t .

P a t h w a y s o f or o fa c i a l p a i n : n e u r o a n a t oP a t h w a y s o f or o fa c i a l p a i n : n e u r oa n a t oP a t h w a y s o f or o fa c i a l p a i n : n e u r o a n a t oP a t h w a y s o f or o fa c i a l p a i n : n e u r oa n a t oP a t h w a y s o f or o fa c i a l p a i n : n e u r oa n a t o

( Di a g r a m 4 )( Di a g r a m 4 )( Di a g r a m 4 )( Di a g r a m 4 )( Di a g r a m 4 )

Sensory inpu t from pe r iphe ra l r ecep t

i s ca r r i ed a long the t r i gemina l pa thway

the somat i c s enso ry a reas o f t he ce reb

cort ex via a 3-neu rone cha in. The cel l bod

from the Tr igeminal (Gasser ian) Gangl

a n d t h i s m a i n n e r v e b u n d l e t h e n e n t e r

b ra ins t em a t t he l eve l o f t he pons . Th

fiber s syna pse for t he f ir s t t ime a t t h e m

s e n s o r y n u c l e u s o f t h e V

t h

n e r(discr imina t ive ta ct i le senses, l ight touch a

p r e s s u r e ) o r a l t e r n a t i v e l y a t d e s c e n d

sp ina l t r ac t nuc le i , t he N . cauda l i s (pa

t e m p e r a t u r e a n d c r u d e t o u c h ) , N . o r a

(cuta neous sens a t ion of ora l mucosa) an d

in t erpolar i s ( tooth pulp pa in) . Second or

f ibers a r i s ing f rom these s i tes then cr

the mid l ine and a scend to synapse a t

t h a l a m u s , f r o m w h i c h t h a l a m o c o r t i

pro ject ions th en pa ss to those cor t ica l a r

concerned wi th orofac ia l sensa t ion and

appreciation. (86-89)

N e u r o p h y s i o l o g i c a l t e c h n i q u e s f o r r e c o r dN e u r o p h y s i ol og i ca l t e c h n i q u e s f or r e c or dN e u r o p h y s i o l o g i c a l t e c h n i q u e s f o r r e c o r dN e u r o p h y s i ol og i ca l t e c h n i q u e s f or r e c or dN e u r o p h y s i o l o g i c a l t e c h n i q u e s f o r r e c o r d

o r o f a c i a l p a i no r o f a c i a l p a i no r o f a c i a l p a i no r o f a c i a l p a i no r o f a c i a l p a i n

Somatosensory evoked potent ia l s (SEP)

The t r igemina l SEP (TSEP) wave form :

The e s sen t i a l f ea tu re s o f TSEP a re

fol lowing sequence of waves. N13, P20 a

N27. Some s t udies h ave a l so observed mu

ear l ie r events , denot ing N5 and P9 (90-9

The peak even t a t 20 ms has been no ted

th e mos t cons i s t en t ly ob ta ined a nd t he m

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cl inical ly used (93,94) . The P20 wave is the

f i r s t cons is ten t s ign of concer ted cor t ica l

a c t i v a t i o n . B e y o n d 3 0 m s t h e E v o k e d

poten t ia l , i s su bject to oth er in fluences such

as e f fe rent and l imbic ac t iv i ty and memory

reca l l , ma king th e behavior a nd m orph ology

of the wa ve form more complex to in t e rpr e t .

These s tud ies ha ve shown th a t TSEP can

b e r e c o r d e d b y s t i m u l a t i o n o f p e r i p h e r a l

b ranches o f t he t r i gemina l ne rve . The s i t e

of s t imula t ion i s usu a l ly the ora l cavi ty . The

most favored be ing th e l ips or gums becaus e

of the i r r e l a t ive ly l a rge senso ry r ecep to r

representa t ion in t he cor t ex. The inf raorb i ta l

n e r v e a t t h e i n f r a o r b i t a l f o r a m e n o r t h em e n t a l i s n e r v e a s i t e m e r g e s f r o m t h e

ma ndibular fora men i s th e oth er s i tes . These

h o w e v e r m a y s h o w m u s c l e a r t i f a c t s

s t imu la t ion an d may r equ i r e th e ne rve to

pierced by a needle . Cer ta in a reas of sca

w h i c h o v e r l i e t h e c e n t r a l g y r u s , h a

b e e n s h o w n t o b e g o o d r e c o r d i n g s i

fo r de t ec t ing TSEP. Refe rence e l ec t ro

a r e p l a c e d i n t h e m i d f r o n t a l p o s i t i(Fpz ) . Pos i t i ons C

5a n d C

6t h a t o v e r

the fac ia l a rea of somatosensory cor tex

the most popular s i tes for ac t ive e lec t ro

(95).

Pa in induced cha nges in TSEP cou ld

observed on s t imula t ion of tooth pulp . Th

p a i n - i n d u c e d c h a n g e s c o u l d f u r t h e r

s t u d i e d i n d i f f e r e n t d i s e a s e d c o n d i t i ome ta bol ic d isorde r s i n pa t i en t s .

C l i n i c a l a p p l i c a t i o n s o f T S E PC l i n i c a l a p p l i c a t i o n s o f T S E PC l i n i c a l a p p l i c a t i o n s o f T S E PC l i n i c a l a p p l i c a t i o n s o f T S E PC l i n i c a l a p p l i c a t i o n s o f T S E P

T h e r e i s s t i l l m u c h t o b e e l u c i d a

a b o u t s o m e f e a t u r e s o f t h e t r i g e m i

s o m a t o s e n s o r y e v o k e d p o t e n t i a l s ( T S E

p a r t i c u l a r l y t h e e a r l y e v e n t s . H o w e v

th e re a re a nu mber of i n s t a nces where th

ha ve proved to be valua ble in th e assessm

of cer ta in condi t ions . Thei r use and fur t

explora t ion i s a dvocated in th ese condi t i

(96-98)

For example a s igni fican t increase in

l a t ency o f t he P20 even t has been t aken

indica te a compress ive les ion in t r igemi

n e u r a l g i a , a n d t h i s f e a t u r e d i s t i n g u i s h

those pa t ien ts most l ike ly to benef i t f r

surgical correct ion. (99) .

The abo l i t i on o f peaks N5 and P9 a

the normal i sa t ion of the la tency of the N

peak h as been t aken to ind ica t e t he su cc

of the t rea t ment by ther mocoagula t ion of

t r igemin al gan gl ion . (100).F ig. 4 : S u m m a r y of t h e ce n t r a l c on n e c t ion s o f

t h e T r i g e m i n a l N e r v e .

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Simi lar ly, preserva t ion an d impr ovement

o f t a c t i l e s e n s i b i l i t y f o l l o w i n g s u r g i c a l

p rocedures may be mon i to red us ing TSEP.

Impai rment of sens ib i l i ty may be indica ted

by reduct ion in am plitu de, la t ency delays and

even aboli t ion of the response (101).

A c o n d i t i o n i n w h i c h a p a t i e n t

e x p e r i e n c e s a n e x a g g e r a t e d r e s p o n s e t o

nox ious s t imu l i i s t e rmed a s Anaes thes i a

dolorosa (AD) . I t usua l ly occurs pos tdenta l

su rge r i e s , i n t r i gemina l t umors and pos t -

her pe t ic neur a lg ias . Increased am pl itu des of

TSEP beyond 50ms in AD is a d iagnos t ic

indicator .

Th i s i s an example where th e sub ject ive

pain sensa t ion may be objec t ive ly assessed

by the den ta l cl in i ci an us ing TSEP s .

P h y s i o l o g i c a l b a s i s o f p a i n r e l i e f : c l i n i c a lP h y s i o l o g i c a l b a s i s o f p a i n r e l i e f : c l i n i c a lP h y s i o l o g i c a l b a s i s o f p a i n r e l i e f : c l i n i c a lP h y s i o l o g i c a l b a s i s o f p a i n r e l i e f : c l i n i c a lP h y s i o l o g i c a l b a s i s o f p a i n r e l i e f : c l i n i c a l

a p p l i c a t i o n sa p p l i c a t i o n sa p p l i c a t i o n sa p p l i c a t i o n sa p p l i c a t i o n s

Control of pain

One of th e most importa nt aspects of pra ct ice

of dent i s t ry i s the cont ro l or e l imina t ion of

pa in . Pa in has been so c lose ly assoc ia ted

w it h d e n t i s t r y t h a t p a i n a n d d e n t i s t r y h a v e

become a lmost s ynonymous . (76)

F o l l o w i n g a r e t h e m e t h o d s o f p a i n

cont ro l :

1) R em ovin g t h e ca u s e

2) Block ing the pa thway of pa in fu l impu l ses

e .g . Local anaes the t ics

3) R a i si n g t h e p a i n t h r e s h ol d e .g . a s p i r in

an d o the r pha rm acolog ica l a gen t s .

4) P r e v e n t i n g p a i n r e a ct i on b y cor t i ca l

depres s ion e .g . gene ra l an aes th es i a

5) U s i n g p s y ch o s om a t i c m e t h o d s e

hypnos is , fa i th hea l ing .

T h e f i r s t t w o m e t h o d s a f f e c t p a

percept ion , th e las t two af fect p a in rea ct i

t h e th i rd a f fect s bo th .

P r e v i ou s / o l d t e c h n i q u e sP r e v i ou s / o l d t e c h n i q u e sP r e v i ou s / o l d t e c h n i q u e sP r e v i ou s / o l d t e c h n i q u e sP r e v i ou s / o l d t e c h n i q u e s

A c r o s s s t u d i e s r e s u l t s s u g g e s t e d t

a c u p u n c t u r e , b i o f e e d b a c k a n d r e l a x a t

were compa ra b le to conse rva t ive t r ea tm

( f o r e x a m p l e a n i n t r a o r a l a p p l i a n c e ) a

w a r r a n t e d f u r t h e r s t u d y . T h e r e w e r e

s t u d i e s f o u n d t h a t c o n d u c t e d r a n d o m i

c l i n i c a l t r i a l s t h a t t e s t e d t h e e f f e c t sh o m e o p a t h y , n a t u r o p a t h y , c h i r o p r a c t

m a s s a g e , m e d i t a t i on , y og a o r h e r

medicines for chr onic facial pa in. Signif ic

gaps in t he scient if ic basis l imit t he a ccur

wi th which denta l profess ionals can gu

t h e i r p a t i e n t s r e g a r d i n g C o m p l e m e n t

a l t e r n a t i v e m e d i c i n e a p p r o a c h e s u s e d

t r ea t chr onic fac ia l pa in (101).

A c u p u n c t u r eA c u p u n c t u r eA c u p u n c t u r eA c u p u n c t u r eA c u p u n c t u r e

I n C l a s s i c a l C h i n e s e M e d i c i n e i t

pos tu la ted tha t a v i ta l force or l i fe ene

(chi ) f lows t hr ough th e body in chan nels

mer id i ans .

Disease i s associa ted wi th d is tu rba nce

th is f low, but for tuna te ly , the fau l t can

correc ted by inser t ing one or more need

in to the mer id i ans conce rned .

S c i e n t i f i c b a s i s : m e c h a n i s m s o f A c u p u n c t uS c i e n t i f i c b a s i s : m e c h a n i s m s o f A c u p u n c t uS c i e n t i f i c b a s i s : m e c h a n i s m s o f A c u p u n c t uS c i e n t i f i c b a s i s : m e c h a n i s m s o f A c u p u n c t uS c i e n t i f i c b a s i s : m e c h a n i s m s o f A c u p u n c t u

E l e c t r o p u n c t u r e h a s b e e n f o u n d

produce ana lges ia in var ious chronic p

syndr omes of mu sculoske le ta l or ig in (10

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This e f fec t i s due to ac t iva t ion of the

pe r i - aqueduc ta l ma t t e r wh ich i s connec ted

to the descending inhib i tory pa th ways of the

lower bra ins tem. (103)

This act ivat ion of the per -aqu eductal grey

mat te r re leases endogenous opiod pept ides

o n t h e i r b i n d i n g s i t e s , r e s u l t i n g i n a n

inh ib i t i on o f t he inh ib i to ry neu rons and a

s u b s e q u e n t d i s i n h i b i t i o n o f t h e o u t p u t

n e u r o n s t o t h e n u c le u s r a p h e m a g n u s

a n d n u cl e u s r a p h e d or s a l i s . F r o m

these r aphe nuc le i o f t he lower pons and

medu l l a , one pa thway sp reads down to the

d o r s a l h o r n of t h e s p i n a l cor d w h e r e

i n c o m i n g p a i n s i g n a l s a r e i n h i b i t e d a n dan oth e r sp reads upwar ds and r e l eases 5 -HT

i n fo r e b r a i n s t r u c t u r e s . Th u s . , w i t h

e l ec t r op u n ct u r e b o t h d e s c e n d i n g a n d

ascending inhib i tory pa thways are involved

in pa in cont ro l (104)

In the s tudy g roup fo r e l ec t ropunc tu re ,

s t e r i l i s e d a c u p u n ct u r e n e e d l e s a r e

int roduced into the points selected accordingt o t r a d i t i on a l Ch i n e s e ch a n n e l s a n d

collat era ls . (105,106)

Acute pa in i s somet imes propor t iona l to

the ex tent of in jury , but the cont r ibut ion of

p s y c h o l o g i c a l f a c t o r s r e v e a l c o m p l e x

re la t ionsh ips tha t a r e profoun dly inf luen ced

by fear , an xiety, cul tu ra l background an d th e

mean ing of the s i tu a t ion to th e person (107).Var ious worker s using evoked potent ial ha ve

repor ted e lec t rophys io logica l cor re la tes of

acupunc tu re (41 ) . These ana lges i a s tud ie s

suggest int era ct ion of oth er sen sory afferen ts

w i t h s p e c i f i c p a i n p a t h w a y s i n b r a i n ,

re l iev ing pa in .

R e c e n t d e v el op m e n t sR e c en t d e v e l op m e n t sR e c e n t d e v el op m e n t sR e c en t d e v e l op m e n t sR e c e n t d e v el op m e n t s

S om e w or k e r s h a v e r e p or t e d t h a t t

appl ica t ion of e lec t r ica l s t imula t ion to

p i tu i t a ry g lan d (PG) ha s p roduced d ram a

rel ief of int ra cta ble pain caused by advan

cancer (108,109). Electr ical st imu lat ion of

p i tu i ta ry g lan d was fol lowed by suppr ess

of tooth pulp evoked potent ials (110) . T

P i tu i t a ry Inh ib i to ry sys t em i s an en t i r

n e w p i c t u r e o f t h e m e c h a n i s m b y w h

elec t r ica l s t imula t ion of the PG resul t s

pa in r e l i e f and cons i s t s o f r ende r ing

hypophysea l sys tem hyperac t ive , which

t u r n a n t i d r o m i c a l l y e x e r t s a n i n h i b i t

i n f luence on the pa in pa thway in the b r(111).

P h a r m a co log y a n d p h a r m a c ot h e r a p e u t i csP h a r m a co lo gy a n d p h a r m a c ot h e r a p e u t i csP h a r m a co log y a n d p h a r m a c ot h e r a p e u t i csP h a r m a co lo gy a n d p h a r m a c ot h e r a p e u t i csP h a r m a co lo gy a n d p h a r m a c ot h e r a p e u t i cs

T h e n a r c ot i c F e n t a n y l r e d u ce s t

sensory in t ens i ty but n ot th e unpleasant n

of pa infu l pulp sen sa t ion (112). In cont ra

a n x i o l y t i c s s u c h a s D i a z e p a m r e d u c

a f fec t ive d i scomfor t r a the r t han sensoi n t e n s i t y q u a l i t i e s o f t h e e x p e r i e n

Simi lar ly p lacebo medica t ion has an imp

o n u n p l e a s a n t n e s s r a t h e r t h a n o n s e n s

qual i t ies of pa infu l events .

T h e r e i s a l s o s u f f i c i e n t e v i d e n c e

e f f i c a c y o f c a r b a m a z e p i n e i n t r i g e m i

neu ra lg ia , a l so for bac lofen an d lam otr ig i

I n T e m p o r o m a n d i b u l a r d i s o r d e r s ( T M

there i s ev idence of a modera te e f fec t

muscle re laxants / t ranqui l i se rs (113) .

R e c e n t a d v a n c e s i n k n o w l e d g e o f

neu ra l processes un der ly ing pa in in th e f

and mou th r evea l a r emarkab le deg ree

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plas t ic i ty fo l lowing in jury or inf lammat ion

o f c r a n i o f a c i a l t i s s u e . I n s i g h t s i n t o

mechanisms involved in th e t ra nsm ission an d

m o d u l a t i o n o f n o c i c e p t i v e s i g n a l s i n t h e

bra ins tem hold promise of the development

of new or improved therapeut ic procedures

for the rel ief of pain (114).

F u t u r e t r e n d s a n d fu t u r e t h e r a p e u t i cF u t u r e t r e n d s a n d fu t u r e t h e r a p e u t i cF u t u r e t r e n d s a n d fu t u r e t h e r a p e u t i cF u t u r e t r e n d s a n d fu t u r e t h e r a p e u t i cF u t u r e t r e n d s a n d fu t u r e t h e r a p e u t i c

d i r e c t i o n sd i r e c t i o n sd i r e c t i o n sd i r e c t i o n sd i r e c t i o n s

A p r om i s i n g a p p r oa c h i s t h e u s e

o f c o r t i c o t r o p h i n - r e l e a s i n g h o r m o n e

a n t a g o n i s t s . T h i s i s b a s e d o n s e v e r a l

u n d e r g o i n g t r i a l s o n c h r o n i c f a c i a l p a i n

pat ients with a nt idepressant s (115,116). It ha sbeen pos tu l a t ed tha t hype rac t iv i ty o f t he

H P A a x i s i n - p a t i e n t s w i t h f i b r o m y a l g i a

corre la tes wi th depress ion .

Th i s l eads us on to the hypo thes i s t ha t

pe rhaps f ac i a l pa in occur s i n suscep t ib l e

i n d i v i d u a l s w h o h a v e a n u n d e r l y i n g

a b n o r m a l i t y o f s t r e s s h o r m o n e r e s p o n s e

resul t ing in h igher cor t i so l leve ls . Recent

d a t a i n d i c a t e v e r y h i g h a n y t i m e c o r t i s o l

leve ls in pa t ien t s wi th fac ia l pa in indica t ing

pat hology in t he h ypoth a lam ic Pi tu i ta r y ax is

(HP A) (117).

As ye t , t he re a re no da t a ava i l ab le on

whet her h igh cor t i sol leve ls pers i s t in fac

p a i n p a t i e n t s t r e a t e d w i t h a n t i d e p r e s s a

a n d t h e m e c h a n i s m o f a n t i d e p r e s s a n t s

modu la t e t he Hypo tha lamic P i tu i t a ry a

ac t iv i ty and inc rease g lucor t i co id i s s

unknown. (118)

T a c k l i n g p a i n a t t h e s o u r c eT a c k li n g p a i n a t t h e s o u r c eT a c k l i n g p a i n a t t h e s o u r c eT a c k li n g p a i n a t t h e s o u r c eT a c k li n g p a i n a t t h e s o u r c e : n e w i d e a s a b: n e w i d e a s a b: n e w i d e a s a b: n e w i d e a s a b: n e w i d e a s a b

n o c i c e p t o r sn o c i c e p t o r sn o c i c e p t o r sn o c i c e p t o r sn o c i c e p t o r s

P2X recept ors a re a fam ily of l igan d ga

ion channels respons ive to ATP, and se

s u b t y p e s t h a t f or m h o m om e t r i c

he t e r omet r i c cha nn e l s ha ve been iden t i f

( 11 9 ) . I n t h e s p i n a l co r d A TP a

p r e s y n a p t i c a l l y t o r e g u l a t e t r a n s m i tr e l e a s e a n d i n v o l v e s N M D A r e c e p

mecha nism . (120-123)

Recent s t ud ies ha ve provided evidence

P 2 X m e c h a n i s m s i n f l u e n c i n g n o c i c e p t

t r a n s m i s s i o n i n t h e t r i g e m i n a l s y s t e

(119,124) . These research s tudies indic

a p p l i c a t i o n o f s e l e c t i v e a n t a g o n

f o r e x a m p l e T N P - A T P ( 2 - ( o r 3 - )

t r ini t rophenyl-ATP) may reversibly at t enu

the percept ion of noc icept ive s t imul i to

tooth pulp. On applicat ion t her e is a decre

i n n e u r o n a l m e c h a n o r e c e p t o r f i e l d a

r e s p o n s e s t o i n n o c u o u s a n d n o x i o

mechanical s t imuli (120,125).

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