A corollary discharge maintains auditory sensitivity during sound production

Interdisciplinary Program in Brain Science

Eye Movement & Vision Research LABHwang, Jae Won

Corollary Discharge Theory

The brain may discriminate self-motion (movement of the eye) from object motion (something moving in the environment) by comparing activity in the eye muscles with retinal image movement. If a corollary motor signal (C) and a sensory signal (S) reach the Comparator at the same time, then eye movement is inferred and not object movement.

http://luna.cas.usf.edu/~husband/percept/corolary.htm

Cricket귀뚜라미의 날개는 앞날개 1 쌍과 뒷날개 1쌍이 있는데 수컷이 소리를 낼 수 있는 것은 앞날개에 있는 줄과 마찰편 때문입니다 . 앞날개는 배 끝까지 덮지는 못하지만 배 옆구리로 날개가 꺾이면서 옆구리까지 덮게 됩니다 . 뒷날개는 퇴화하여 작아지거나 반대로 발달하는 것도 있습니다 . 뒷날개의 역할은 귀뚜라미가 나는 데 사용할 수 있다는 것입니다 .

http://home.dongguk.edu/user/ento/file2/c.figure.htm

귀뚜라미의 귀는 특이하게도 앞다리 종아리 마디에 있습니다 . 사진은 앞다리의 바깥쪽 (오른쪽 사진 ) 과 안쪽 ( 왼쪽 사진 ) 을 보여주고 있는데 사진에서 보이는 하얀 고막이 바로 귀입니다 .

Release of Singing Behavior

Microinjections of neuroactive substances like cholinergic agonists or ACh esterase blockers into the brain are most effective in grasshoppers and in crickets. Stridulation may last for many minutes and different song patterns are released.

Calling song stridulation is released in the cricket Gryllus bimaculatus by microinjection of eserine into the protocerebrum.

http://www.zoo.cam.ac.uk/zoostaff/hedwig/index.html

Suction Electrode

The Suction Electrode is used to record or stimulate a tissue which remains submerged in saline. It is a popular choice to overcome the difficulties associated with air and oil recordings. With the Suction Electrode, it is quite easy to record extracellularly from very small hearts (insects), intestinal nerves, eye neurons and to stimulate muscles by an electrical pulse to their neurons.

http://www.a-msystems.com/physiology/products/electrodes/suction.asp

Auditory System of Cricket

Ear(right)

Prothoracic

Ganglion

Omega 1Neuron

60 AuditoryAfferent Neuron

Ear(left)

Omega 1Neuron

60 AuditoryAfferent Neuron

synapse

synapse

(along 5th prothoracic nerve)

(along 5th prothoracic nerve)

Two Fundamental ProblemsSpeaking and singing present the auditory system of the caller with two fundamental problems :

• Discrimination between self-generated and external auditory signals

• Prevention against desensitization

Sonorous Singing

• Intracellular recordings were made from the dendritic region of ON1

• An Inhibitory input influenced auditory processing. - Max spike fq. of ON1(176±28Hz) was much lower than at rest(376 ±50Hz).

-Vertical Scale bar intracellular : 25mV extracellular : 10mV wing : 1mm

- Horizontal Scale bar : 250ms

Silent Singing• Sound production was prevented by removing one forewing.

• ON1 received inhibitory postsynaptic potentials(IPSPs) during the syllables. - The activity of ON1 during sonorous stridulation is due to the cricket’s own song.

• ON1 response to external acoustic stimuli was inhibited during the chirps. - Only excitatory postsynaptic potentials, and occasionally a spike, were elicited by the stimuli during silent chirps.

Fictive Singing• To determine whether the inhibition was elicited by sensory feedback or by the network of neurons that generate the motor pattern.

• Either thoracic or thoracic and abdominal galglia was isolated from muscles and sense organs, except for the fifth prothoracic nerve.

• IPSPs were also present in the fictively singing cricket.• IPSPs even persisted when the ear were removed.

Auditory Afferents

• Primary afferent depolarizations (PADs) were presented with a similar timing to the IPSPs in ON1.- Vertical Scale bar intracellular : 15mV extracellular : 10mV wing : (a) 1mm, (b) 0.25mm, (c) 0.5mm

- Horizontal Scale bar : 250ms

Auditory Afferents(cont’d)

• The PADs did not affect spike production in the auditory afferents.

• But in many sensory systems, PADs have an inhibitory function as they reduce synaptic efficacy at the afferent terminals.

Effectiveness of Inhibition

-Vertical Scale bar intracellular : 25mV wing : 1mm

- Horizontal Scale bar : 100ms

• At rest and during the chirp interval each sound pulse evoked a burst of spike in ON1 with an average maximum spike frequency of 376±50Hz.

• During silent chirps ON1 responded with bursts of only 123±29Hz.

Effect of Inhibition on ON1

• At 80dB SPL each sound pulse elicited a burst of spikes with 203±24Hz.

• When normal singing was mimicked with 100dB SPL chirps, the response to the following 80dB SPL test stimuli was reduced to 30±1Hz.

-Vertical Scale bar intracellular : 25mV current : 20nA

- Horizontal Scale bar : 100ms

Effect of Inhibition on ON1(cont’d)

• Injected hyperpolarizing current prevented ON1 from spiking during the 100dB SPL chirp. The average maximum response to subsequent 80dB SPL stimuli was a burst of spikes at 143±32Hz, which was significantly higher than the response without current injection.

Conclusion• In the cricket an efferent signal(a ‘corollary discharge’) modulates auditory information processing at two levels of the auditory system : PADs in auditory afferent terminals and IPSPs in ON1.

• Inhibition by the corollary discharge reduces the neural response to self-generated sound and protects the cricket’s auditory pathway from self-induced desensitization.