HORACIO VANEGAS * Department of Psychiatry,WARREN E. FOOTE** Yale University School of Medicine,JOHN P. FLYNNt New Haven, Connecticut 06510

HYPOTHALAMIC INFLUENCES UPON ACTIVITY OF UNITS OF THE VISUAL CORTEXt

Electrical stimulation of critical sites within the hypothalamus of cats elicitsa well coordinated attack upon a rat.' A cat will attack a rat in preferenceto other objects2 and the choice of object (in some instances, the experi-menter) can be determined by the site stimulated.! Vision is used by thecat in locating its target and, under certain experimental conditions, open-ing of the mouth prior to biting depends on vision.4 The mechanism where-by specific hypothalamic stimulation elicits such a critical use of vision isunknown.

If the visual selection of attack objects, visually guided approach by acat to a rat, and visually guided opening of the mouth prior to biting, weredue to hypothalamic influences upon the visual system, then one would ex-pect hypothalamic stimulation to modify the activity of the visual system.

It has been shown that stimulation of attack sites within the hypothalamusmodifies visual cortical potentials evoked by stimulation of the optic tractor optic radiations, and that the direction of the change is in the oppositedirection to that induced by stimulation of the midbrain reticular forma-tion.6 In the present study individual units of the visual cortex were ex-amined to see if their activity was altered by stimulation of the hypothala-mus. These visual units are sensitive to movement and particular shapesand orientations of the stimulus as well as to light flashes and steady lights.If the units responded to previously optimal stimuli in a different fashionduring hypothalamic stimulation, the possibility that these changes wereinvolved in the cats visually selecting a target remains open.

METHODTwenty adult cats were used. The first 12 of them were anesthetized with urethane

(0.8 gr/kg of body weight) and were given paralyzing doses of gallamine triethiodideafter all surgical procedures had been completed. These 12 animals were artificiallyrespirated. The last eight cats were under a state of coma produced by bilateralradiofrequency lesions of the midbrain. These lesions were made while the cat was

* Research Associate, Present Address: Instituto Venezolano De InvestigacionesCientificas, Apartado 1827, Caracas, Venezuela.

** Post-doctoral Fellow, Biological Sciences Training Program.t Associate Professor.t Supported by U. S. Public Health Service grants MH 07114-09 and 2 ROL MH

08936-06.Received for publication 20 August 1969.

191

YALE JOURNAL OF BIOLOGY AND MEDICINE Decemberl969-Februaryl970

under ether anesthesia, and involved the whole tegmentum and most of the centralgray. The superior colliculi, the cerebral peduncles and the interpeduncular nucleuswere generally spared.The eyes were stabilized by the paralytic agent in the first 12 animals. In the eight

comatose animals, the midbrain lesion interfered with the pathways from the hypo-thalamus to the midbrain and oculomotor system.The animal was placed in a stereotaxic frame modified for unobstructed vision,

atropine was applied to the left eye, and both eyes were covered with contact lenses.Small trephine holes were made in appropriate sites in the cranium for the introduc-tion of recording microelectrodes and stimulating hypothalamic electrode. A tangentscreen was held 1 or 1.5 meters before the cat, and-in some animals-a lens of 1 or0.6 D, respectively, was placed before the left eye, the right eye being covered by ablack patch. In other animals no corrective lens was used, both eyes being uncovered.A variety of visual stimuli could be projected onto the screen. Diffuse light was pre-sented either in an "on-off" fashion (1:1 sec.) or in the form of flashes of 3 /,secduration. Pattern stimuli such as light bars on a dark background, dark bars on a lightbackground, dark edges, etc. were projected onto different sites on the screen, and atvaried angles of rotation around the optical axis. These stimuli were shown "on-off"(1:1 sec.), or were moved tangentially to the cat's eye and perpendicularly to theorientation of the stimulus' longest dimension, until the optimal stimulus for any givencortical unit was found. In many cases a 60 Hz voltage was fed into a photocell whichcould be placed at a critical locus on the screen so as to signal the presence of theoptimal stimulus. No attempts were made to determine the exact dimensions andorientation of the stimulus with reference to optical coordinates, but during each ex-periment great emphasis was placed upon the reliability of the unit's response and theinvariability of the stimulus' placement and orientation. A simplified diagram of onlythe stimulus' shape and orientation will be given in the illustrations.Hypothalamic stimulation was carried out through stainless steel bipolar concentric

electrodes by means of a Grass S8 Stimulator with Grass Stimulus Isolation Units.The stimulus consisted of biphasic symmetrical rectangular waves, each half lasting1 msec.; the repetition rate was either 50 to 60 Hz, for trains of about 3 sec. duration(long trains) or 200 Hz for trains of about 100 msec. duration (short trains). Thepeak-to-peak current, measured as voltage drop across a 100lf resistor placed in serieswith the cat, was constantly monitored on a Tektronix oscilloscope. Constant currentstimulation was approximated by the use of two 39 KQ resistors in series with the cat.

Extracellular unit recordings were made from the caudal portion of the lateralgyrus, and the postlateral, suprasplenial and splenial gyri of the right cerebral hemis-phere. Tungsten microelectrodes were used for the first five cats; subsequently, glassmicropipettes filled with either 3M KCl or 4M NaCl were used. The micropipettes'tips were less than 1 u in diameter, and the impedances were approximately 2 to 30MQ at the beginning of each penetration. In order to minimize respiratory and cardio-vascular displacements a plastic pressor foot was applied to the surface of the lateralor postlateral gyri.78 The dura mater was removed when tungsten microelectrodeswere to be used, but the penetrations with micropipettes were done through the dura.Microelectrodes were introduced by means of a hydraulic microdrive. Recordings weremade through amplifiers with high input impedance, capacity compensation and unitygain-namely, the IL PICO-metric Amplifier or the ELSA-4 Bak Amplifier. Differen-tial amplification was used to minimize stimulus artifact during concurrent stimulationof the visual system and the hypothalamus. Unit activity was displayed on Tektronix

192

Hypothalamus and zisual cortical units V

oscilloscopes both directly from the amplifier and after being put through a Krohn-hite filter with a pass-band of 150-20,000 Hz, and photographed from the storagescreen with a Polaroid system. Sometimes the unit activity was recorded on an FMAmpex tape recorder, and later played back into an S&E Ultraviolet Recording Oscil-lograph.

Intracarotid blood pressure was monitored on occasion by means of a Stathamtransducer coupled to a Sanborn recorder whose output was fed into the oscilloscopeon which the unit recordings were displayed.At the end of each experiment a small DC lesion was made through the hypothalamic

electrode and the cat was perfused with saline and 10% formalin. Hypothalamic place-inents were identified in Prussian Blue, Cresyl Violet and Weil stained brain sections.*

RESULTSThe effects of hypothalamic stimulation were investigated only on those

units that could be identified as uninjured, 123 in total. The sampling wasbiased during the actual experiment toward units that were most easilyinfluenced by visual and/or hypothalamic stimulation. When tungsten mi-croelectrodes were used, the action potentials had a leading negative phasefollowed by a smaller positive phase,9 or were biphasic negative-positive,with a peak-to-peak amplitude of several hundred microvolts. When micro-pipettes were used, the leading phase of the action potentials was generallypositive and 1 to several millivolts high, this being followed by a slightnegative phase.9"0 These characteristics were distorted in the filteredrecord from which the illustrations were made. In the illustrations positivityis upward. The duration of the leading phase was 0.5 to 1 msec.; shorterspikes were suspect of being fiber activity, longer ones of being injuredcells. Injury was recognized by the usual criteria.7"'l

Hypothalamic effects upon responses of visual cortical units to patternedstimuliFrom the point of view of possible hypothalamic influences on visual

perception, units of the visual cortex such as those described by Hubel andWiesel1"' as being responsive to orientation, movement, or shape of visualstimuli are of particular interest. Seventy-six units of this sort were studied.Fifty-six of them showed altered responses to visual stimuli as a result ofhypothalamic stimulation. Twenty of them were not affected in their pat-tern of response to the visual stimuli by hypothalamic stimulation. While

* At the end of each microelectrode penetration attempts were made to place a DClesion so as to permit appropriate investigation of the depths at which recordings hadbeen made. This was successful only when tungsten microelectrodes were used, sincethe high impedance of our micropipettes often prevented the flow of sufficient current.A method for adequate depth marking with micropipettes is still under trial in ourlaboratory, and since our notes on recording depths are solely based upon the highlyunreliable readings on the micromanipulators, no reference as to this aspect will bemade in the present report.

193

VANEGAS., FOOTE., FLYNN

VALE JOURNAL OF BIOLOGY AND MEDICINE December1969-Februaryl970

the change, when it occurred, was consistent for any given unit, the direc-tion of the change induced by hypothalamic stimulation varied from unit tounit. The responsiveness of 26 units was enhanced by hypothalamic stimula-tion, i.e. the number of impulses to the combined visual and hypothalamicstimulation exceeded the sum of responses to the separate visual and hypo-thalamic stimulations. The response of thirty other units was similarlydecreased by hypothalamic stimulation. Examples of enhancement, diminu-

ENHANCED DIMINISHED NO CHANGE

s 7cc~~~~4m~~~~~ I'lill''lsl''

COTh OtSHThq

s ~ Hh _

PREC.

'joomsece

JII

PRPc.EC.I

HTh -

i|"!

8T

PRC

o00 msec

s.- I "11 X +; 8 ~~~~~~~~~~~~~~~_PREC. fjs

Th HThm_

S S S K> fS

5 sec

FIG. 1. Examples of the influences of hypothalamic stimulation on the activity ofcells responding to slits, moving slits, and moving edges. The hypothalamic effectupon any one unit was always in the same direction. The number of the unit is cir-cled. Below the number is a representation of the optimal visual stimulus for that unit.S denotes the stimulus presentation. A widening of the S trace is associated with in-creased illumination. Cont. HTh means that the hypothalamus was being stimulatedthrough the time depicted, while Prec. Hth means that a long train to the hypothala-mus preceded the presentation of S shown on the line. The on-off response of unit 96to a horizontal slit is enhanced by hypothalamic stimulation. Unit 123 shows a strikingenhancement of its response to a moving edge. Similarly there is a marked diminutionof the response of unit 98 when the hypothalamus is stimulated continuously. A longtrain to the hypothalamus diminished the response to movement of the stimulus in onedirection and abolished it to movement in the other direction.

194

Hypothalamus and visual cortical units A

tion, and no change as a result of hypothalamic stimulation are given inFigure 1.

Hypothalamtic effects upon visual cortical units responding to flashes andsustained diffuse light

Thirty-six units responded to 3 Lsec. flashes of light projected upon thetangent screen. There were four units whose response to a flash was en-hanced by hypothalamic stimulation. The activity of 19 units was dimin-ished by hypothalamic stimulation; and effect was mixed in the case of 11units. In only two instances was no change observed. Examples of the en-hanced, diminished, and mixed effects are given in Figure 2. Since theresponse to a flash may consist of the arrest of the units' activity as well asincreased firing,"1-7 enhancement means in this instance that the hypo-thalamic effect was to increase the number of impulses shown in responseto a flash. Diminution has an analogous meaning. The effect is referred toas "mixed" when the hypothalamic influence showed different effects atdifferent periods within 900 msec. after the flash.

Five units were found that responded to diffuse illumination lasting forone second. "On" responses, "on-off" responses, and "off" responses wereobserved. With concurrent hypothalamic stimulation, the firing of two unitswas enhanced, that of two others diminished, and that of the fifth was un-changed. Examples are presented in Figure 3.

Effects of hypothalamic stimnulation on the activity of units firing spon-taneously

Forty-eight units fired in the absence of changes in illumination and ofhypothalamic stimulation. The rate varied from one every ten seconds totwelve per second, in conformity with the rates observed by Hubel andWiesel.1' The relative number of spontaneously active units was the samein the anesthetized and in the comatose preparation.The effect of hypothalamic stimulation, which was consistent for any

given unit, was to increase the rate of firing of 23 units, to decrease therate of 11 units, and to leave 14 units unchanged. Examples of the variouseffects are given in Figure 4.With short hypothalamic trains, the effect of stimulation in some cases

was roughly uniform for the duration of the entire sweep of the oscilloscope(generally 1 sec.), in other cases the effect varied with time (Figure 5).The effect that was roughly consistent for the duration of the oscilloscopesweep (generally 1 sec.) could be either enhancement (e.g., unit 79) ordiminution (unit 81). When the effect of hypothalamic stimulation wastime variant, there seemed to be two types. One type showed an initial

195

VANEGAS,, FOOTE., FLYNN

YALE JOURNAL OF BIOLOGY AND MEDICINE December 1969-February1970

ENHW

I0.

SX

s

5-

(A

S-

5.

0.

E

10

FLASHfNCED DIMINISHED MI)

CONTINUOUS HTh STIMULATION

10 100

55

BHTh l a HTn e

.J2 Ls500 900 0 500900 0

M" nsc p pm

SHORT HTh151

:1 rfl~a HTh

50 900niC

10xlox

5U,

Y O0.U)

10

STIMULATION

a HTh

mc0 900M"c

XED

aHTh

BC

5x

5

e '0

0 a HTh

o 9Uis"

FIG. 2. Examples of the effects of hypothalamic stimulation on units responding toflashes. The responses of a unit (indicated by a circled number) to a 3 '&sec. flash areshown in two histograms. For each unit the upper histogram represents the responseto flash alone. The lower histogram represents the response to flash during hypothal-amic stimulation 4Continuous HTh) or just following a 100 ms. stimulus to the hypo-thalamus (Short HTh). Below the number of the unit is the number of samples onwhich each histogram is based. The number on the ordinate corresponds to the num-ber of spikes seen during 50 msec. intervals from the time of the flash (F).

ENHANCED

I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

a ..A I f

DIMINISHED

a" ams

z,e - -. -'UZZI2a_ a I M I

-

I~~~~~~~~~~~

I1' I I I I

Ise

*''''1 in ---I INs_

FIG. 3. The different effects of continuous hypothalamic stimulation on the responsesof three units to changes in diffuse illumination of the visual field, which lasted ap-proximately one second, are shown above. The symbols are the same as in Fig. 1.

196

S

a_vw,--- I I I_ 1 Ait O 1M%AM& - a m m buillism"ft CONTm I m I I 'I 1- i H"

Hypothalamus and visual cortical units A

ENHANCED DIMINISHED NO CHANGE

-~~~~~~~A NO SThMUAT.4i.4u.~~~u

_ -CAT ST1WILT0-HO'f Za3 _l~~~~~~I 11 --i ll_ |_

II ~ ~ ~ x

FIG. 4. Examples of the effects of hypothalamic stimulation on the "spontaneous"activity of visual cortical units. The symbols are as in Fig. 1. HTh indicates thestimulus artifact. In the case of unit 81, the top trace shows an artifact. In this tracethe stimulator was on but the electrodes were disconnected. In the second trace thestimulator was on and the electrodes were connected. Note the marked increase infiring rate of units 46 and 31 (larger one in 31-32) due to hypothalamic stimulation.Unit 81, on the other hand, was rendered, inactive by the hypothalamic train: It sloweddown during stimulation and remained inactive for more than 15 sec., progressivelyrecovering thereafter. Unit 44 did not respond spontaneously or after hypothalamicstimulation, but was easily activated by movement of an oriented slit.

CONSISTENT IME VARLANr

SPONT I1

HuHH

00o micFIG. 5. Examples of the effects of short hypothalamic trains (ca. 100 ins.) upon the

spontaneous activity of visual cortical units. SPONT refers to activity in the absenceof hypothalamic stimulation or changes in illumination. HTh denotes preceding hypo-thalamic train (stimulus artifact apparent at beginning of trace). A roughly uniformeffect of enhancement (79) and diminution (81) are seen on left. In the case of units80 and 83 the effect has a time course. The temporal effect is opposite in the two in-stances. The histograms between units 80 and 83 were constructed in the followingway. For a few units that responded in the way unit 80 did, the number of spikes inSPONT was subtracted from the number of spikes in HTh (in corresponding inter-vals of 50 msec.). The result is the net change in a unit's activity due to the hypo-thalamic train. The differences for different units were added for each interval, andthese make up the continuous line histogram. The broken line histogram was similarlyconstructed from the few units that behaved like unit 83. The shaded area representsthe period of the stimulus artifact, during which the number of spikes is rather un-certain.

197

VANEGASj FOOTE,, FLYNN

YALE JOURNAL OF BIOLOGY AND MEDICINE

00;

December 1969-February 1970

cdKc

0

0.

x>O 0

U1 *_

a) .4 a)X

CIO 0(A~

X X°*-b +v

U.Ono °

xoacn %44@-oa) =

> = D

boxXFH H-

198

Hypothalamus and visual cortical units I VANEGAS, FOOTE, FLYNN

activation with a peak around 150 msec. after the beginning of the hypo-thalamic train (e.g. unit 80). The other type was initially depressed, withthe lowest value around 250 msec. (e.g., unit 83). Since only a few unitsof each type have been found, this classification must be regarded only astentative.

Sites stimulated wtithin the hypothalamusThe sites stimulated within the hypothalamus are shown in Figure 6. The

electrode directly in the medial mammillary nucleus is not in a site fromwhich attack has been elicited in our laboratory. Similarly, in only a fewcases has attack been noted by stimulation of the posterior hypothalamicnucleus. The other sites correspond to regions from which attack of onesort or another has been elicited in our laboratory.

DISCUSSION

The fact that electrical stimulation of structures outside the visual sys-tem can influence individual neurons of the visual cortex has been shownon several occasions. The spontaneous activity of units in the visual cortexas well as their responses to diffuse light of long and short duration can bemodified by electrical stimulation of the nonspecific thalamic nuclei,"' themesencephalic reticular formation'2' and the caudate nucleus.' We havenow shown this to be true also for hypothalamic stimulation. In the lasteight animals this effect was further shown to be independent of an intactmidbrain reticular formation. The modification of the activity of units whichrespond optimally to orientation, movement, and shape of visual stimuli ishighly relevant to visually-guided behavior. The present study is, in fact,the first demonstration that the response of such units is susceptible toother than visual influences. It is possible that modification of the activityof the units might result in an emphasis to some patterns and movementsand a de-emphasis to others, which would in turn bias the output of thevisual cortex.One fact that emerges from an analysis of several reports is the division

of cortical visual units into two groups such that, in response to a givenstimulus, the neurons of one group show firing at the time when the neuronsof the other group are depressed. In response to a flash, for example,Jung's'5 neuronal types C and D (cf. 16, Figure 2) are depressed aroundthe time when the B-neurons are activated, i.e., up to about 60 msec. afterthe flash, whereas this relation is reversed around 100-120 msec. after theflash. Single shocks to the nonspecific thalamic nuclei (cf. 19, Figure 1)produce activation of neuron types II and IV within the first 100 msec.,and this is followed by a depression (also seen in type V) of about 200

199

YALE JOURNAL OF BIOLOGY AND MEDICINE December1969-February1970

msec. duration that coincides with the activation of type III neurons.Stimulation of the caudate nucleus also gives rise to a depression of ac-tivity in some neurons (ibid. Figure 1, b and c) coincident with an activa-tion of others (ibid. Figure 1, d). It would seem as if a firing burst in oneneuronal group might have an inhibitory effect upon the neurons of theother group. The phenomenon illustrated in the present report, Figure 5,right, seems to represent an analogous neuronal behavior, although thesmall size of the sample does not warrant a clear statement at this point.

Finally, a word must be said about the fact that, although the hypo-thalamic points stimulated agree with the topography of visually-guidedattack, no attempt was made to determine the actual behavior of the catsused in this study. Such an attempt did not seem warranted until the evi-dence concerning hypothalamic influences upon visual cortical units wasavailable. This evidence is provided by the present investigation.

SUMMARY

Electrical stimulation of critical sites within the hypothalamus of a catgives rise to a visually guided attack by the stimulated cat on a rat. Ittherefore seemed possible that the activity of the hypothalamus might exertan influence upon neurons sensitive to visual forms and movement. To testthis hypothesis the activity of 123 units was recorded extracellularly fromthe primary visual cortex. Unit responses to oriented slits, edges, and move--ment could be clearly modified by hypothalamic stimulation in a directionthat was consistent for each unit. Responses to diffuse light in the form offlashes or sustained illumination were similarly modified, as was the spon-taneous activity of visual cortical units.

REFERENCES

1. Wasman, M. and Flynn, J. P.: Directed attack elicited from hypothalamus. Arch.Neurol. Psychiat., (Chic.), 1962, 6, 220-227.

2. Levison, P. K. and Flynn, J. P.: The objects attacked by cats during stimulationof the hypothalamus. Anim. Behav., 1965, 13, 2-3.

3. Flynn, J. P., Vanegas, H., Foote, W., and Edwards, S.: Neural mechanisms in-volved in a cat's attack on a rat; chapter in Neural Control of Behavior, NewYork, Academic Press (In Press).

.4. MacDonnell, M. and Flynn, J. P.: Sensory control of hypothalamic attack. Anim.Behav., 1966, 14, 399-405.

5. Chi, C. C. and Flynn, J. P.: The effect of hypothalamic and reticular stimulationon evoked responses in the visual system of the cat. Electroenceph. clin.Neurophysiol., 1968, 24, 343-356.

'6. Lindsley, D. B., Schreiner, L. H., Knowles, W. B., and Magoun, H. W.: Be-havioral and EEG changes following chronic brain stem lesions in the cat.Electroenceph. clin. Neurophysiol., 1950, 2, 483-498.

7. Amassian, V. E.: Evoked single cortical unit activity in the somatic sensory areas.Electroenceph. clin. Neurophysiol., 1953, 5, 415-438.

8. Branch, C. L. and Martin, A. R.: Inhibition of Betz cell activity by thalamic andcortical stimulationi.J. Neurophysiol., 1958, 21, 380-390.

200

Hypothalamus and visual cortical units VANEGAS, FOOTE, FLYNN

9. Hubel, D. H.: Single unit activity in lateral geniculate body and optic tract ofunrestrained cats. J. Physiol. (Lond.), 1960, 150, 91-104.

10. Guld, C.: A glass-covered platinum microelectrode. Medical Electron. biol.Engng., 1964, 2, 317-327.

11. Brookhart, J. M., Moruzzi, G., and Snider, R. S.: Spike discharges of singleunits in the cerebellar cortex. J. Neurophysiol., 1950, 13, 465-486.

12. Frank, K. and Fuortes, M. G. F.: Potentials recorded from the spinal cord withmicroelectrodes. J. Physiol. (Lond.), 1955, 130, 625-654.

13. Hubel, D. H. and Wiesel, T. N.: Receptive fields, binocular interaction and func-tional architecture in the cat's visual cortex. J. Physiol. (Lond.), 1962, 160,106-154.

14. Hubel, D. H. and Wiesel, T. N.: Receptive fields and functional architecture intwo non-striate visual areas (18 and 19) of the cat. J. Neurophysiol., 1965,28, 229-289.

15. Jung, R.: Neuronal discharge. Electroenceph. clin. Neurophysiol., 1953, Suppl.4, 57-71.

16. Baumgartner, G.: Reaktionen einzelner Neurone im optischen Cortex der Katzenach Lichtblitzen. Arch. ges. Physiol., 1955, 261, 457-469.

17. Polyanskii, V. B.: Connection between spike discharges and evoked potentials inrabbit visual cortex. Fed. Proc. Transl. Suppl., 1966, 25 (5 II), 753-757.

18. Hubel, D. H. and Wiesel, T. N.: Receptive fields of single neurons in the cat'sstriate cortex. J. Physiol., 1959, 148, 574-591.

19. Akimoto, H. and Creutzfeldt, O.: Reaktionen von Neuronen des optischen Cortexnach elektrischer Reizung unspezifischer Thalamuskerne. Arch. Psychiat.Nervenkr., 1958, 196, 494-519.

20. Creutzfeldt, 0. and Akimoto, H.: Convergenz und gegenseitige Beeinflussung vonImpulsen aus der Retina und den unspezifischen Thalamuskernen an einzelnenNeuronen des optischen Cortex. Arch. Psychiat. Nervenkr., 1958, 196, 520-538.

21. Creutzfeldt, O., Spehlmann, R., and Lehmann, D.: Veranderung der Neuron-aktivitat des visuellen Cortex durch Reizung der Substantia reticularis mesen-cephali. In Neurophysiologie und Psychophysik des visuellet Systems, Berlin,Springer, 1961, pp. 351-363.

22. Fuster, J. M.: Excitation and inhibition of neuronal firing in visual cortex byreticular stimulation. Science, 1961, 133, 2011-2012.

23. Lehmann, D. and Koukkou, M.: Neuronale Effekte der Caudatumreizung unvisuellen Cortex. Pfliigers Arch. ges Physiol., 1964, 280, 297-315.

201