EPSPs of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cat

Stimulation of the infraorbital nerve at strengths 1.4–2.5 times higer than the threshold of excitation of A fibers in cats anesthetized with chloralose and pentobarbital evoked EPSPs with an amplitude up to 3.0 mV and a duration of 9–15 msec in 69% of masseter motoneurons after 1.5–3.0 msec. These EPSPs were complex and formed by summation of simpler short-latency and long-latency EPSPs. The short-latency EPSPs appeared in response to infraorbital nerve stimulation at 1.1–1.5 thresholds and had a slow rate of rise (2.5–4.5 msec, mean 3.7±0.4 msec), low amplitude (under 2.0 mV), and short duration (5–6 msec). Their latent period varied from 1.5 to 3.0 msec (mean 2.1±0.2 msec). The shortness of the latent period and its constancy during stimulation of the nerve at increasing strength, and also the character of development of facilitation and inhibition of the EPSP during high-frequency stimulation suggests that these EPSPs are monosynaptic. The slow rate of rise suggested that these EPSPs arise on distal dendrites of the motoneurons. Long-latency EPSPs appeared 7–9 msec after stimulation of the infraorbital nerve at 1.1–1.5 thresholds. Their amplitude reached 1.5–2.0 mV and their duration 7–9 msec. The long duration of the latent period combined with low ability to reproduce high-frequency stimulation (up to 30/sec) points to the polysynaptic origin of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 583–591, November–December, 1977.     

Unit responses in the auditory cortex to stimulation of geniculocortical fibers

Extracellular and intracellular single unit responses of neurons of the auditory cortex to electrical stimulation of geniculocortical fibers (GCF) were recorded in experiments on cats immobilized with tubocurarine. The latent period of responses of 15% of neurons to GCF stimulation was 0.3–1.5 msec. It is postulated that they were excited anti-dromically. The latent period of spikes generated by neurons responding to GCF stimulation orthodromically varied from 1.6 to 12 msec. In 28.6% of neurons the latent period was 1.6–2.5 msec. It is postulated that these neurons were excited monosynaptically. Intracellular recording revealed primary IPSPs in response to GCF stimulation in 63.3% of neurons, a brief EPSP followed by a prolonged IPSP in 17.7%, an EPSP-spike-IPSP complex in 12.3%, and subthreshold EPSPs in 7% of neurons. The latent period of the primary IPSPs varied from 1.8 to 11 msec, being 1.8–3.7 in 72%, 3.8–5.7 in 20.0%, and 5.8–11 msec in 8.0% of neurons. The latent period of responses beginning with an EPSP was 1–4 msec (mean 1.8 msec). Orthodromic responses arising 3–10 msec after the antidromic response, and consisting of 3–5 spikes, were recorded in some antidromically excited neurons. Hypotheses regarding the functional organization of the auditory cortex and mechanisms of inhibition in its neurons are put forward on the basis of the results obtained.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 227–235, May–June, 1972.     

Suppression of "fast" IPSP,superposed on "slow", as a possible cause of priming in murine hippocampus

Intra- and extracellular response in area CA1 to stimulation of two independent afferent inputs, one a priming or conditioned and the other a test or primed input (C1 and C2, respectively) were recorded in surviving murine hippocampal slices. Duration and amplitude of test field potentials (FP) and of excitatory postsynaptic potentials (EPSP), were measured, as well as amplitude of "fast" and "slow" components of inhibitory postsynaptic potentials or stimulation varying between 0 and 1 sec. Conditioning brought about an increase in the duration of FP, in duration and amplitude of EPSP, and suppression of IPSP at intervals of between 50 and 500 msec peaking at 200 msec (i.e., priming effect). These changes correlated with level of IPSP_b in response to conditioned stimuli. The most pronounced effect could be seen in neurons manifesting hyperpolarizing IPSP in response to test stimuli. Suppression of test IPSP_a after superposition on IPSP_b is thought to bring about the increase in test FP and EPSP seen during priming.Institute for Brain Research, All-Union Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 730–739, November–December, 1990.     

Aspects of excitation and inhibition produced in parietal association cortex neurons by stimulating thalamic association nuclei

Neuronal response to single stimuli applied to the thalamic dorsolateral and posterolateral nuclei (DLN and PLN resepctively) was investigated in the parietal association cortex. Primary IPSP following DLN and PLN stimulation was noted in 62.5% and 79.6% of instances respectively. Latencies of EPSP and IPSP when stimulating the two nuclei were longer for the DLN. The amplitude of EPSP evoked by stimulating association nuclei rose and declined smoothly, while that of IPSP showed a fast rise and a more steady decline. The EPSP appearing during the evolution of IPSP were of higher amplitude than control level of resting potential. Both amplitude and duration of IPSP induced in a single unit by stimulating different association nuclei were extremely similar, thus confirming the involvement in this operation of the same inhibitory cortical interneurons. Duration of IPSP was shorter than that of inhibitory background spike activity. It is postulated that the discrepancy in duration can largely be ascribed to properties of the neurons themselves.State University, Odessa. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 529–536, September–October, 1991.     

Corticofugal postsynaptic influences on red nucleus neurons

The responses of red nucleus neurons to stimulation of the sensorimotor cortex was studied on nembutal-anesthetized cats. Most of the rubrospinal neurons were identified according to their antidromic activation. Stimulation of the sensorimotor cortex was shown to evoke in the red nucleus neurons monosynaptic excitatory potentials with a latency of 1.85 msec, polysynaptic excitatory potentials (EPSP), and inhibitory postsynaptic potentials (IPSP) with a latency of 9–24 msec. The EPSP often produced spikes. The probability of generation of spreading excitation is greater with motor cortex stimulation. The monosynaptic EPSP are assumed to arise under the influence of the impulses arriving over the corticorubral neurons as a result of excitation of axodendritic synapses. The radial type of branching of red nucleus neurons facilitates the transition from electrotonically spreading local depolarization to an action potential triggered by the initial axonal segment. Polysynaptic EPSP and IPSP seem to be a result of activation of fast pyramidal neurons whose axon collaterals are connected via interneurons with the soma of the red nucleus neurons.L. A. Orbeli Institute of Physiology of the Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 43–51, January–February, 1971.     

Unit responses in the cat auditory cortex to medial geniculate body stimulation

Responses of 98 auditory cortical neurons to electrical stimulation of the medial geniculate body (MGB) were recorded (45 extracellulary, 53 intracellularly) in experiments on cats immobilized with tubocurarine. Responses of the same neurons to clicks were recorded for comparison. Of the total number of neurons, 75 (76%) responded both to MGB stimulation and to clicks, and 23 (24%) to MGB stimulation only. The latent period of extracellularly recorded action potentials of auditory cortical neurons in response to clicks varied from 7 to 28 msec (late responses were disregarded), and that to MGB stimulation varied from 1.5 to 12.5 msec. For EPSPs these values were 8–13 and 1–4 msec respectively. The latent period of IPSPs arising in response to MGB stimulation varied from 2.2 to 6.5 msec; for 34% of neurons it did not exceed 3 msec. The difference between the latent periods of responses to clicks and to MGB stimulation varied for different neurons from 6 to 21 msec. Responses of 11% of neurons to MGB stimulation, recorded intracellularly, consisted of sub-threshold EPSPs, while responses of 23% of neurons began with an EPSP which was either followed by an action potential and subsequent IPSP or was at once cut off by an IPSP; 66% of neurons responded with primary IPSPs. Neurons responding to MGB stimulation by primary IPSPs are distributed irregularly in the depth of the cortex: there are very few in layers III and IV and many more at a depth of 1.6–2 mm. Conversely, excited neurons are predominant in layer III and IV, and they are few in number at a depth of 1.6–2 mm. It is concluded that the afferent volley reaching the auditory cortex induces excitation of some neurons therein and, at the same time, by the principle of reciprocity, induces inhibition of others. This afferent inhibition takes place with the participation of inhibitory interneurons, and in some cells the inhibition is recurrent. The existence of reciprocal relationships between neurons in different layers of the auditory cortex is postulated.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 23–31, January–February, 1972.     

Corticofugal influences on the motoneurons of the trigeminal nucleus

We studied the postsynaptic potentials evoked from 76 trigeminal motoneurons by stimulation of the motor (MI) and somatosensory (SI) cortex in the ipsilateral and contralateral hemispheres of the cat. Stimulation of these cortical regions evoked primarily inhibitory postsynaptic potentials (PSP) in the motoneuron of the masseter muscle, but we also observed excitatory PSP and mixed reactions of the EPSP/IPSP type. The average IPSP latent period for the motoneurons of the masseter on stimulation of the ipsilateral cortex was 6.1±0.3 msec, while that on stimulation of the contralateral cortex was 5.2±0.4 msec; the corresponding figures for the EPSP were 7.6±0.5 and 4.5±0.3 msec respectively. Corticofugal impulses evoked only EPSP and action potentials in the motoneurons of the digastric muscle (m. digastricus). The latent period of the EPSP was 7.6 msec when evoked by afferent impulses from the ipsilateral cortex and 5.4 msec when evoked by pulses from the contralateral cortex. The duration of the PSP ranged from 25 to 30 msec. Postsynaptic potentials developed in the motoneurons studied when the cortex was stimulated with a single stimulus. An increase in the number of stimuli in the series led to a rise in the PSP amplitude and a reduction in the latent periods. When the cortex was stimulated with a series of pulses (lasting 1.0 msec), the IPSP were prolonged by appearance of a late slow component. We have hypothesized that activation of the trigeminal motoneurons by corticofugal impulsation is effected through a polysynaptic pathway; each functional group of motoneurons is activated in the same manner by the ipsilateral and contralateral cortex. The excitation of the digastric motoneurons and inhibition of the masseter motoneurons indicates reciprocal cortical control of their activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 512–519, September–October, 1971.     

Electrophysiological properties of neurons and neuronal organization of the crayfish somatogastric ganglion

Experiments with intracellular recording from neurons of the isolated crayfish somatogastric ganglion established that the membrane potential of the neurons is 53±3 mV. Single stimulation of the central branches of the ganglion evoked EPSP and a spike in the neurons. The spike amplitude was 7.5±0.6 mV. The small amplitude of the spike is explained by the fact that it arises at some distance from the body of the neuron and propagates electrotonically in it. Summation of several EPSP is necessary in most cases for initiation of the spike. When the orthodromic stimulus was strong enough, and IPSP occurred in some cells in addition to the EPSP and spike. Stimulation of the peripheral nerves of the ganglion induced in most neurons antidromic excitation and in some neurons orthodromic excitation. Some neurons spontaneously discharged rhythmically with an unstable frequency (11–27 impulses/sec). An investigation of the effect on neurons of chemical agents [acetylcholine, adrenalin, noradrenalin, gamma-aminobutyric acid (GABA), glutamic acid, and dopamine] showed that acetylcholine has the strongest and most stable depolarizing action and apparently is a synaptic transmitter in the ganglion. The other agents excited some neurons — depolarized them and evoked rhythmic discharges — and, coversely, hyperpolarized and suppressed the rhythmic activity of other neurons. A scheme of neuronal organization of the somatogastric ganglion of the crayfish is proposed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 307–313, May–June, 1970.     

Mechanism of inhibition following reflex discharge in spinal cord interneurons

Using the method of microelectrode (intracellular and extracellular) recording, the mechanism of inhibition following reflex discharge in interneurons of the lumbosacral section of the spinal cord of cats on activation of cutaneous and high-threshold muscle afferents was studied. It was shown that the postdischarge depression of the reflex responses 10–20 msec after the moment of activation of the neuron is due to afterprocesses in the same neuron and presynaptic pathways. The depression of spike potentials from the 20th to the 100th msec is produced by inhibitory postsynaptic potentials (IPSP). During the development of IPSP the inhibition of spike potentials can be due to both a decrease of the depolarization of the postsynaptic membrane below the critical threshold and a decrease of sensitivity of the cell membrane to the depolarizing action of the excitatory postsynaptic potential (EPSP). At intervals between the stimuli of 30–100 msec the duration of EPSP after the first stimulus does not differ from that after the second stimulus. Hence, it is suggested that the presynaptic mechanisms do not play an essential part in this type of inhibition of interneurons. The inhibition following the excitation favors the formation of a discrete message to the neurons of higher orders.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 3–9, January–February, 1970.     

Corticofugal influences on postsynaptic processes in rubrospinal neurons in the cat brain

Composite and unitary EPSPs of red nucleus neurons evoked by stimulation of the sensomotor and association parietal cortex and nucleus interpositus of the cerebellum were studied in acute experiments on cats anesthetized with pentobarbital. A monosynaptic connection was shown to exist between not only the sensomotor, but also the association cortex, and rubrospinal neurons, in which unitary EPSPs appeared during stimulation of the association cortex after a latent period of 1.5–2.7 msec, with a peak rise time of 1.1–3.1 msec and an amplitude of 0.22–0.65 mV. Analysis of the temporal characteristics of the unitary EPSP suggested that synapses formed by fibers from the association cortex occupy a position nearer the soma than synapses formed by axons of sensomotor cortical cells.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 67–74, January–February, 1984.     

Inhibitory synaptic potentials of the smooth muscle cells of guinea pig taenia coli

A single submaximal intramural application of rectangular stimuli (duration 0.2–0.5 msec) to an atropine-treated taenia coli muscle band evoked inhibitory postsynaptic potentials (IPSP) and a marked relaxation of the muscle band in the vast majority of muscle cells. The latency period of the IPSP was 122±16 msec; the times for a rise and fall of amplitude were 96±8 and 370±60 msec, respectively. The mean latency period of muscle relaxation was 800 msec. The latency period, and especially the amplitude of the IPSP depended on the intensity of the intramural stimulation. This indicates that one muscle cell is inhibited by several nerve fibers. IPSP evoked by threshold stimuli displayed a tendency toward summation, while the amplitude of the second and of subsequent IPSP evoked by low-frequency maximal stimuli was always less than that of the first IPSP. After periodic stimulation (frequency 10–60 impulses/min) was discontinued, a posttetanic decrease in IPSP amplitude was observed. Anodic polarization of the muscle band with a direct current raised the effectiveness of synaptic transmission, as was evidenced by the considerable increase in IPSP amplitude. When the muscle membrane was hyperpolarized with noradrenaline, IPSP inhibition was reversible. This is evidence that the unknown mediator and noradrenaline have a common ionic inhibitory mechanism.A. A. Bogomol'ts Institute of Physiology of the Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 5, pp. 544–551, September–October, 1970.     

Synaptic responses of medullary neurons of turtles to stimulation of the locomotor region

Responses of medullary neurons to microstimulation of the locomotor region by a current of up to 30 µA were studied by intracellular recording in turtles. The resting potential recorded in these neurons was from 22 to 42 mV. Depolarization PSPs (EPSPs) were recorded in 43 neurons, hyperpolarization PSPs (IPSPs) in 12, and mixed in 36. Synaptic discharges were observed in 29 neurons. Of these cells 11 generated action potentials without visible PSPs. The latent period of the PSPs was most frequently between 2 and 8 msec. The time from the beginning of the EPSP to the beginning of the action potential was 1–3 msec if the response index was high, but in the case of weaker stimulation, it began to fluctuate strongly and lengthened. Unitary EPSPs were recorded in 15 neurons and IPSPs in three. Their amplitude was 0.6–0.8 mV, from 2 to 12 times less than the depolarization threshold (1–7 mV). These results, together with those obtained previously by extracellular recording of medullary unit activity in turtles and cats, are used to discuss the possible mechanism of spread of locomotor activity.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 122–129, March–April, 1982.     

Characteristics of inhibition in the kitten sensory-motor cortex

Responses of 340 neurons of the sensory-motor cortex to electric shocks applied to the limbs were investigated in kittens aged 3–30 days. In 9.4% of cells of kittens aged 3–10 days and in 17.1% of cells in kittens aged 21–30 days pauses were observed immediately after the excitatory component of the extracellular response. Intra- and quasiintracellular recording showed that postsynaptic inhibition participates in the genesis of these pauses. The IPSPs which, as a rule, followed the excitatory component of the response were of much longer duration (up to 250–380 msec) than the analogous IPSPs in the sensory-motor cortex of adult cats. Usually the amplitude of the IPSP in kittens did not exceed 5 mV.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 227–231, May–June, 1977.     

Excitatory postsynaptic potentials of hippocampal neurons and their extinction during repeated stimulation

A method of detecting "minimal" excitatory postsynaptic potentials (EPSP) in neurons of hippocampal area CA₃ of the unanesthetized rabbit during stimulation of the septo-fimbrial region and the dentate fascia is described. The method consists of presenting a strong (a current of up to 1 mA) conditioning stimulus, inducing a distinct inhibitory postsynaptic potential (IPSP), before a near-threshold (current of 0.03–0.35 mA) testing stimulus. The response to the testing stimulus, develoing after the previous conditioning IPSP, in most cases was purely depolarizing and, judging from the change in the latent period in some cases and the absence of correlation between its amplitude and that of the IPSP, it is a pure EPSP. If the testing stimuli are presented at low enough frequency (intervals of not less than 1 sec) the amplitude of the EPSP evoked by them gradually falls. This decrease exhibits some of the characteristic properties of extinction of behavioral responses (recovery after an interruption, a more rapid decrease during repeated series of stimuli, a slower decrease in amplitude during less frequent stimulation). The amplitude of the IPSP also fell or showed no significant change. The results are evidence in support of the hypothesis that extinction is based on a mechanism of homosynaptic depression.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 3–12, January–February, 1978.     

Monosynaptic inhibitory postsynaptic potentials of cortical neurons

Monopolar intracortical stimulation of the auditory cortex was carried out in cats immobilized with D-tubocurarine. A macroelectrode (tip diameter 100 µ) or a microelectrode (tip diameter 10–15 µ) was used for stimulation. In both cases, besides excitatory responses, primary IPSPs with latent periods of 0.4–1.2 and 1.4–6.0 msec were recorded in cortical neurons close to the point of stimulation. The first group of IPSPs are considered to be generated in response to direct stimulation of bodies or axons of inhibitory cortical neurons, i.e., monosynaptically. The amplitude of these IPSPs varied in different neurons from 3 to 15 mV, and their duration from 4 to 150 msec. Additional later inhibitory responses were superposed on many of them. Of the IPSPs generated in auditory cortical neurons in response to stimulation of geniculocortical fibers 1.5% had a latency of 0.8–1.3 msec. They also are assumed to be monosynaptic. It is concluded that the duration of synaptic delay of IPSPs in cortical neurons and spinal motoneurons is the same, namely 0.3–0.4 msec. Axons of auditory cortical inhibitory neurons may be 1.5 mm long. The velocity of impulse conduction along these axons is 1.6–2.8 m/sec. The genesis of some special features of IPSPs of cortical neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 5, pp. 458–467, September–October, 1975.     

Responses of neurons in the auditory cortex to sound stimuli

The evoked potential (EP) and the pulse activity of single auditory cortex neurons were recorded simultaneously in response to a click and to a tone for cats under nembutal and nembutal — chloralose anesthesia. Both extra- and intracellular taps were employed. The experiments showed that the reaction of auditory cortex neurons in response to a click lasts from 200 to 300 msec. It consists of pulse discharges from several groups of neurons. Out of 174 neurons observed 8 responded within 4 to 7 msec after a click (before the EP). One hundred and nine neurons reacted in the range from 7 to 25 msec which coincided with the initial electropositivity of the EP; 11 neurons were in the range from 40 to 100 msec and 4 were between 180 and 270 msec. Such a sequence of involvement of different neuron groups in the reaction is probably accounted for to a large extent by the time dispersion of the afferent volley. With an intracellular tap slow alterations of membrane potential were observed in the form of an EPSP with pulses together with subsequent hyperpolarization lasting 50 to 70 msec and slowly increasing depolarization that reached a maximum after 170 to 200 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 147–157, September–October, 1969.     

Short-latency unit responses of the lateral geniculate body to electrical stimulation of the optic tract in rats

Short-latency responses of single relay neurons of the lateral geniculate body to electrical stimulation of the optic tract were studied. The response of many neurons was complex and could consist of a series of (1–3) spikes with fixed latent periods. Each spike of such a response can be recorded on the EPSP in the absence of other spikes, preserving its latent period. The fixed latent periods of different relay neurons may vary from one to another. In the intervals between spikes with these latent periods active inhibition (IPSP) takes place. The series of spikes, EPSP, and IPSP is completed, as a rule, by a long IPSP.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 28–32, January–February, 1973.     

Unit responses in the anterior zone of the suprasylvian gyrus to peripheral stimuli of different modalities

Unit responses in the anterior zone of the suprasylvian gyrus to visual, electrodermal, and acoustic stimulation were investigated in experiments on unanesthetized cats immobilized with tubocurarine. Electrical activity was recorded from 131 units, 121 of which were spontaneously active. In 65.5% of cells responses consisted of a short or long increase or a decrease in intensity of spike activity. Most cells (58.2%) were monosensory. Responses to visual stimulation were given by 72% of neurons, to electrodermal by 61.6%, and to acoustic by 9.3%. The corresponding latent periods were 20–40, 20–30, and 15–20 msec. Responses of the same neurons to different peripheral stimuli were uniform or they differed in their dynamics. Intracellular recording gave responses in the form of EPSPs (amplitude 4–5 mV, duration 60–80 msec) or, rarely, IPSPs (amplitude 2–3 mV, duration 160–200 msec). The functional organization of the associative cortex and mechanisms of analysis of incoming afferent information are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 368–374, July–August, 1972.     

Inhibition in the fish olfactory bulb

Inhibition in the olfactory bulb of the carp was studied by recording potentials from secondary neurons intracellularly. Three types of inhibition — trace, early, and late — can arise in neurons of the olfactory bulb. Trace inhibition corresponds to hyperpolarization about 20 msec in duration, which is closely connected with the spike, but it is not after-hyperpolarization but an IPSP. Early and late inhibition correspond to IPSPs of different parameters. The first has a latency of 0–50 msec (relative to the spike) and a duration of 60–400 msec; the corresponding values for the second are 100–400 msec and 0.5–3 sec. The possible mechanisms of these types of inhibition are discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 650–656, November–December, 1971.     

Temporal summation in cat visual cortical neurons

Characteristics of temporal summation in neurons of area 17 of the visual cortex in acute experiments on unanesthetized, immobilized cats. During light adaptation, extracellular spike responses of these neurons to optimal local photic stimuli of varied duration — from 5 to 1000 msec — were studied. The critical duration of temporal summation of excitation, determined by the supraliminal method using the criterion of maximal discharge frequency in the first volley of the spike response, varied in different cells from 5 to 100 msec; neurons with summation lasting 15–100 msec (mean 31.45±5.67 msec) were found most frequently. Neurons with central receptive fields differed significantly from cellswith peripheral fields in the shorter critical duration of temporal summation, the lower frequency of spontaneous discharges, and the shorter duration of the first volley of the response. Summation time in neurons with simple receptive fields was significantly shorter than in neurons with complex receptive fields. The results of these experiments are compared with data in the literature obtained by the study of retinal and lateral geniculate neurons in cats and are discussed from the stand-point of division of ascending afferent projections in the visual system into X-and Y-groups (Ia and Ib).Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 345–352, July–August, 1981.