Neuronal responses of a chronically isolated slab of auditory cortex to intracortical stimulation during paroxysmal electrical activity in cats

Responses of 155 neurons 3 weeks after neuronal isolation of a slab of auditory cortex (area AI) to single intracortical stimulating pulses at the level of layer IV were studied in unanesthetized, curarized cats during paroxysmal electrical activity evoked by series of high-frequency (10–20 Hz) electrical stimulation by a current 2–5 times above threshold for the direct cortical response. In response to such stimulation a discharge of paroxysmal electrical activity, lasting from a few seconds to tens of seconds, appeared in the slab. As a rule it consisted of two phases — tonic and clonic. This indicates that cortical neurons can form both phases of paroxysmal cortical activity. Depending on behavior of the neurons during paroxysmal electrical activity and preservation of their ability to respond to intracortical stimulation at this time, all cells tested in the isolated slab were divided into four groups. Their distribution layer by layer and by duration of latent periods was studied. Two-thirds of the neurons tested were shown to generate spike activity during paroxysmal discharges whereas the rest exhibited no such activity. A special role of neurons in layer II in generation of paroxysmal activity in the isolated slab was noted. The view is expressed that at each moment functional neuronal circuits, independent of each other, exist in the slab and also, evidently in the intact cortex, which can interact with one another when conditions change.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 3–11, January–February, 1984.     

Neuronal inhibitory responses to intracortical stimulation of an isolated slab of cat auditory cortex

Neuronal responses of an isolated slab of cortex to intracortical stimulation were studied intracellularly. The predominant responses were primary IPSPs. Their latent periods did not exceed 10 msec. Within the volume of cortex studied, neurons inhibited in response to stimulation were most numerous in the upper layers (II, III). Predominance of disynaptic IPSPs is evidence of the important role of cortical interneurons in their genesis. It is concluded from the results that primary IPSPs limit the spread of excitation primarily in the activated area of cortex. Since involvement of neurons of the isolated slab in the inhibition process takes place for only 10 msec after stimulation, neurons giving spike responses to intracortical stimulation with a longer latent period can transmit information into other brain zones. The role of duration of IPSP in the dynamics of interneuronal interaction in the cerebral cortex is discussed.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1. pp. 42–49, January–February, 1984.     

Neuronal responses of an isolated slab of cat auditory cortex to intracortical stimulation

Neuronal responses of an isolated slab of auditory cortex (area AI) to intracortical stimulation at the level IV were studied in curarized cats by extracellular recording 3 weeks after isolation. Dispersion of response latencies in the isolated slab was reduced (compared with that observed soon after isolation); the predominant responses were mono- and disynaptic, and the number of discharges consisting of bursts of spikes increased. However, despite simplification of the structural and functional organization of the chronically isolated slab of auditory cortex, the conditions for complex polysynaptic interaction between neurons of all layers were preserved in it, and in each layer the character of such interaction depended on the distance of the neuron from the focus of origin of the excitation. [In the chronically isolated slab of auditory cortex, just as in the acutely isolated slab, late reponses of over 40 msec were absent.]I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 462–469, September–October, 1982.     

Neuronal responses in an isolated slab of the cat auditory cortex to intracortical stimulation

Neuronal responses in an isolated slab (area AI) to intracortical pulsed electrical stimulation at the level of layer IV were investigated extracellularly in acute experiments on cats immobilized with D-tubocurarine. Responding neurons were found in all layers of the slab. The character of their distribution by depth in the slab depended on the distance between recording and stimulating electrodes. The latent period of responses of different neurons ranged from 0.8 to 25 msec. With interelectrode distances of 0.5–2 mm most neurons responded mono- and disynaptically. However, responses of many neurons had a latent period of over 4 msec, i.e., they were polysynaptic. This indicates the complex character of interneuronal interactions, even in a limited area of the cortex. After intracortical stimulation no after-discharges with a latent period of over 40 msec could be recorded in the isolated slab of auditory cortex.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 85–93, January–February, 1982.     

Effect of pentobarbital on neuronal inhibitory response evoked in an isolated slab of cat auditory cortex by intracortical stimulation

Neuronal responses of an acutely isolated slab of auditory cortex (area AI) to intracortical electrical stimulation were studied intracellularly in cats anesthetized with pentobarbital. It was found that 77% of responses were primary IPSPs, and allowing for secondary inhibitory responses, an inhibitory response was observed in 92% of neurons. All types of neuronal responses in the slab were short-latency. The maximal response latency did not exceed 5 msec. Neurons responding to stimulation by IPSPs were found at all depths in the slab, with a maximum in layers II–III. Nearly all primary IPSPswere mono- and disynaptic. Pentobarbital increased the duration of individual neuronal inhibitory responses in the isolated slab of auditory cortex without affecting maximal duration of the IPSP. The mechanisms of the effect of pentobarbital on the amplitude and duration of IPSPs are discussed.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 147–152, March–April, 1984.     

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.     

Cholinergic neurons in an association cortex slab chronically isolated from the cat

Small numbers of short- and long-axon cholinergic interneurons were revealed on a slab of association cortex three weeks after (neuronal) isolation from the cat by means of a histochemical acetylcholinesterase reaction. Short-axon neurons are located at layers II–VI and take the form of mainly spindle-shaped medium sized cells with their axons forming synaptic terminals on pyramidal and stellate neurons of the isolated section. Typical positioning of cholinergic terminals on the perikaryon and proximal portions of cholinoceptive neuron dendrites was noted. Pyramidal cholinoceptive cells may be classed as noncholinergic cells, whereas stellate cells may be either cholinergic or noncholinergic. Long-axon cholinergic interneurons of different shapes and sizes are situated at layers I and VI. Neuronal axons located in these layers run within fibers of the first and subcortical layers, establishing intracortical connections beyond the confines of the isolated section.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 60–66, January–February, 1989.     

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.     

Effects of repetitive stimulation of the locus coeruleus on spinal inhibitory responses to suprasegmental stimulation in cats

Effects of repetitive stimulation of the locus coeruleus on spinal responses to activation of cortico-, reticulo-, and vestibulospinal tracts were studied in decerebellate cats anesthetized with chloralose. Descending influences of these structures were assessed from changes in amplitude of extensor and flexor monosynaptic discharges or from the magnitude of postsynaptic potentials recorded from the corresponding motoneurons. Stimulation of the motor cortex or modullary reticular formation as a rule evoked two-component inhibitory responses in extensor motoneurons and excitatory-inhibitory responses in flexor motoneurons. Stimulation of locus coeruleus effectively depressed the amplitude of the late component and, to a lesser degree, that of the early component of inhibition arising after stimulation of the cerebral cortex or reticular formation. During stimulation of the locus coeruleus no marked changes were found in inhibitory responses evoked by vestibulospinal influences in flexor motoneurons, and also in excitatory responses arising after stimulation of the above-mentioned descending pathways in both groups of motoneurons.     

Phase patterns of neuronal responses reliably discriminate speech in human auditory cortex

How natural speech is represented in the auditory cortex constitutes a major challenge for cognitive neuroscience. Although many single-unit and neuroimaging studies have yielded valuable insights about the processing of speech and matched complex sounds, the mechanisms underlying the analysis of speech dynamics in human auditory cortex remain largely unknown. Here, we show that the phase pattern of theta band (4-8 Hz) responses recorded from human auditory cortex with magnetoencephalography (MEG) reliably tracks and discriminates spoken sentences and that this discrimination ability is correlated with speech intelligibility. The findings suggest that an approximately 200 ms temporal window (period of theta oscillation) segments the incoming speech signal, resetting and sliding to track speech dynamics. This hypothesized mechanism for cortical speech analysis is based on the stimulus-induced modulation of inherent cortical rhythms and provides further evidence implicating the syllable as a computational primitive for the representation of spoken language.     

Generation and spread of direct responses of the intact and chronically isolated cortex

Mechanisms of generation and conduction of direct cortical responses were studied in acute experiments on unanesthetized curarized cats with an intact cortex or with a chronically isolated strip of cortex. All the properties of these responses of the intact and isolated cortex of the suprasylvian gyrus were found to be identical. Inhibition of muscarinic cholinergic receptors in the region of the cortex between the stimulating and recording electrodes prevents or considerably reduces the conduction of excitation through this area, which is explained by the polysynaptic mechanism of conduction of the direct response. Cortical neuronal networks over which direct responses spread are anisotropic in direction. Application of the anticholinergic drug benactyzine to the cortex inhibits, whereas application of the anticholinesterase agent galanthamine increases not only the original direct cortical responses, but also responses previously reversed by application of -aminobutyric acid or pentobarbital or by coagulation of the cortical surface. Both deep and surface components of the direct response are thus generated by cholinergic structures in the cortex itself.Institute of Physiology, Academy of Medical Sciences of the USSR, Siberian Branch, Novosibirsk. Translated from Neirofiziologiya, Vol. 7, No. 5, pp. 451–457, September–October, 1975.     

Inhibitory processes in neuronal reactions of the auditory cortex in the cat undergoing dichotic stimulation

In experiments on anaesthetized cats, studies have been made of intracellular and extracellular responses of single units in the auditory cortex during dichotic stimulation simulating sound source motion. Responses of some cortical units exhibit strong dependence on the signal parameters related to spatial and directional characteristics of simulated sound source motion. Profound inhibition was invariably revealed at the beginning of sonic stimulation as well as during certain moments of its movement. The role of inhibition in formation of cortical reactions to sound source motion is discussed.