Effects of changes in carrier frequency and modulation rate on unit responses in the inferior colliculus to amplitude-modulated sounds

Unit responses in the rat inferior colliculi to amplitude-modulated sounds were investigated. Two parameters of these sounds were varied: the modulation and carrier frequencies. The first ranged from 1–5 to 100 Hz, while the range of the second was determined by the frequency-threshold curve of the neuron. Other parameters of the amplitude-modulated stimulus (depth of modulation, level of carrier intensity) were kept as constant as possible. Characteristics of the unit response are determined by the nature of the combination of the carrier and modulation frequencies used. If the carrier frequency was optimal, the range of reproduction of the modulation frequencies, the number of spikes in the response, the duration of the response, and the corresponding stimulus duration were maximal; the response appeared at an earlier phase of the modulation cycle. A change in carrier frequency from optimal toward both higher and lower frequencies induced a regular change in all characteristics of the response: narrowing of the range of reproduction of the modulation rhythm amounting in some cases to total cessation of response, a decrease in the number of spikes per response, and shortening of the response in some cases as far as the appearance of only the initial response, while the response itself occurred in later phases of the modulation cycle.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 12–22, January–February, 1972.     

Responses of central auditory neurons to frequency-modulated stimuli

Unit responses of the inferior colliculi of albino rats to frequency-modulated stimuli were investigated. The number of spikes, firing pattern, and duration of the discharge were determined. Parameters of unit responses obtained with different directions of frequency modulation were compared with the results of testing the effect of constant-frequency tones on the neurons. The distinguishing features of the unit responses to stimuli with different directions of frequency modulation were compared with the characteristics of the frequency-threshold curve and the lateral inhibitory zones, taken as indices of the unit responses to constant-frequency tones. With a change in stimulus frequency upward or downward from the initial level the unit responses to both directions could be similar as regards the number of spikes per discharge and the firing pattern or could differ sharply depending on the direction or, finally, they could arise only if the stimulus frequency changed in one direction. In some cases selectivity for the direction of the change in stimulus frequency was due to the width and position of the lateral inhibitory zones. However, for one-third of the neurons tested analysis of the spatial characteristics of the excitatory and inhibitory zones alone was insufficient to explain the high selectivity in the formation of a response to a stimulus with frequency modulation in one direction only.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.3, pp.237–245, May–June, 1974.     

Analysis of unit activity in the cat lateral geniculate body

Spontaneous and evoked single unit activity of lateral geniculate body neurons was recorded extracellularly in acute experiments on cats. Eight groups of neurons differing in the durations of the minimal and mean interspike intervals of spontaneous unit activity, and in the latent period and duration of the first volley of spikes of evoked activity, were distinguished by analysis of the data. On the basis of this classification a scheme for interaction between neurons of the lateral geniculate body is suggested.Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 30–37, January–February, 1978.     

Responses of central auditory neurons to frequency-modulated stimuli and temporal characteristics of inhibitory interaction

Responses to frequency-modulated stimuli of 118 inferior collicular neurons were compared with quantitative characteristics of the frequency — threshold curves and lateral inhibitory zones during time-varying two-tone stimulation in anesthetized albino rats. In one third of neurons high sensitivity to the direction of frequency modulation does not correspond to their spatial characteristics (the shape, width, and arrangement of the lateral inhibitory zones relative to the frequency — threshold curve). The specificity of response of these neurons to a particular direction of frequency modulation is evidently based on differences in the temporal course of inhibition evoked by high-frequency and low-frequency tones.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 603–607, November–December, 1975.     

Effect of local surface cooling of the rat cortex on the impulse activity of neurons assumed to be the sources of corticofugal influences

In an experiment on albino rats with electrodermal stimulation of the forepaw evoked potentials (EP) in the neostriatum (NS), the cortical primary response (PR), and impulse reactions of neurons (mainly of layers V and VI of the cortex) were recorded. The zone of leading-off of the potentials in the cortex was subjected to local surface cooling, which led to an increase in the PR amplitude. This facilitation was accompanied by a change in the time parameters of the impulse reactions of the cortical neurons: the latency and duration increased, and a rhythmic organization of activity appeared or intensified (if it was already present). The increase in the PR amplitude and number of spikes in the response of the cortical neurons to stimulus presentation was far less intensive than the sharp increase in EP amplitude in the NS, and did not correspond to it fully in time. The data suggest that the activating influence of the corticofugal signal on EP in the NS is determined not so much by the intensity of the descending signal as by its temporal organization.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 181–189, March–April, 1991.     

Single unit responses in the auditory center of the frog mesencephalon to amplitude-modulated tones

Responses of most single neurons of the torus semicircularis ofRana ridibunda to stimuli of characteristic frequency and with low (10–30%) sinusoidal amplitude modulation were considerably stronger than those of the same neurons to pure tones. Analysis of phase histograms synchronized with the period of modulation was used to study dependence of the response on the frequency of modulation. In some cells the degree of modulation of the phase histogram fell steadily with an increase in modulation frequency, but in others a maximum was found in the 10–20 Hz region. Usually modulations of the phase histogram were significantly greater than stimulus modulation. The phase angle between the maximum of stimulus amplitude and the maximum of the unit response increased as an approximately linear function of the increase in modulation frequency.N. N. Andreev Acoustic Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 264–271, May–June, 1980.     

Characteristics of inhibition in receptive fields of the cat visual cortex

Unit responses of neurons of zone 17 in the cat striate cortex to stripes of different widths were studied. Changes in the number of spikes during different time intervals (cuts) from the beginning of the response were analyzed in relation to stimulus area. Comparison of the results with those obtained by the study of receptive fields of the lateral geniculate body showed a significant difference in the dynamics of inhibition between cortical and geniculate receptive fields. Similar results were obtained when cortical unit responses to simultaneous and consecutive appearance of two stripes in the receptive field, one in the excitatory zone and the other at the inhibitory periphery, were studied. Evidence of the longer duration of cortical inhibition also was obtained by the same technique. When both stripes were placed in the excitatory center of the field another feature of cortical inhibition was revealed: its dependence on the order of stimulus application. If the order of stimulus application coincided with the optimal direction of movement of the stripe for the given field, the unit response to the next stimulus was strongly facilitated by the action of the stimulus applied previously. Application of stimuli in the opposite order invoked inhibition. The sensitivity of inhibition to the order of stimulus application was observed in the center of the field; it diminished toward the periphery, where application of the stimuli in any order evokes inhibition of the response.Medical Academy, Sofia, Bulgaria, I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 339–346, July–August, 1977.     

Characteristics of unit responses of the cat cerebellar cortex to acoustic stimuli

Investigation of unit responses of the cerebellar cortex (lobules VI–VII of the vermis) to acoustic stimulation showed that the great majority of neurons responded by a discharge of one spike or a group of spikes with a latent period of 10–40 msec and with a low fluctuation value. Neurons identified as Purkinje cells responded to sound either by inhibition of spontaneous activity or by a "climbing fiber response" with a latent period of 40–60 msec and with a high fluctuation value. In 4 of 80 neurons a prolonged (lasting about 1 sec or more), variable response with a latent period of 225–580 msec was observed. The minimal thresholds of unit responses to acoustic stimuli were distributed within the range from –7 to 77 dB, with a mode from 20 to 50 dB. All the characteristics of the cerebellar unit responses studied were independent of the intensity, duration, and frequency of the sound, like neurons of short-latency type in the inferior colliculi. In certain properties — firing pattern, latent period, and threshold of response — the cerebellar neurons resemble neurons of higher levels of the auditory system: the medial geniculate body and auditory cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 3–12, January–February, 1973.     

Involvement of thalamic neurons and the striopallidal complex in maintaining constancy of visual perception in the human brain

Neuronal activity was investigated in different thalamic nuclei and the striopallidal complex in parkinsonian patients with long-term implantation of intracerebral electrodes in the structures concerned for diagnostic and therapeutic purposes. Directionally selective neurons were found with consistent response to presentation of visual stimuli oriented at the same angle in a variety of (spatial) head positions differing by 90°.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 93–101, January–February, 1989.     

Dependence of inhibitory zones of inferior collicular unit responses on temporal parameters of acoustic stimuli

Single unit activity was studied in the inferior colliculi of anesthetized albino rats in response to pure tones of different frequencies. The dependence of inhibitory interaction between neurons on temporal parameters of the acoustic stimuli (duration, time interval between tones) was investigated. Quantitative characteristics of the lateral inhibitory zones, defined as ranges of frequencies inhibiting spike generation in response to the optimal or near-optimal frequency, were examined. The inhibitory zones were found to depend essentially on the interval between application of the conditioning and testing stimuli. With an increase in the interval the inhibitory interaction decreased. If the duration of the acoustic stimuli was shortened, interaction was reduced as regards both the width of the frequency band and the intensity evoking the inhibitory effect.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 236–244, May–June, 1972.     

Characteristics of interaction between central neurons and abdominal stretch receptors in the crayfish

Spontaneous activity of slow- and fast-adapted abdominal stretch receptor (SAR and FAR) of the crayfish and their activity evoked by adequate stimulation were investigated in the presence of efferent regulation. Activity of the receptors was shown to be under effective inhibitory control of two central neurons, principal and accessory; activity of these neurons, in turn, is determined by the current receptor activity. The closest interaction is found between SAR and the principal inhibitory neuron. Two types of efferent regulatory action of this neuron were discovered: grouped and continuous. Its powerful discharges (up to 361 spikes) arising in response to only one SAR afferent impulse are described. The character of synaptic connections between the peripheral and central neurons is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Institute of Zoology, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 317–327, May–June, 1972.     

Involvement of calcium-binding membrane components in neurophysiological mechanics of habituation in Helix pomatia

Dynamics of binding between calcium and hydrophobic membrane components were investigated in vivo in identified neurons ofHelix pomatia while producing habituation to tactile stimuli using a fluorescent chlortetracycline probe technique. A decline in the concentration of membrane-bound calcium (Ca _b ²⁺ ) and likewise in the intensity of electrophysiological response was found in the "command" neurons of defensive behavior when applying a train of stimuli. An increase in Ca _b ²⁺ was noted in the sensory neuron studied and in the spiracle motoneurons. It proved difficult to produce habituation in these cells fulfilling standard electrophysiological criteria. Hydrophobe-hydrophil transfer of calciumbinding molecules is thought to accompany production of habituation in nerve cells.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 605–612, September–October, 1989.     

Dependence of unit responses of the catlateral geniculate body on photic stimulus contrast

Unit responses in the lateral geniculate body of cats to photic stimuli of different contrast were investigated. The number of spikes in the initial phase of the responses (the first 30–45 msec) was found not to change at first, but then to decrease with an increase in the intensity of background illumination. The background intensity starting from which the response diminishes was shown to increase with an increase in the intensity of the test stimulus. The unit response is a linear function of the logarithm of stimulus contrast if the contrast is changed through variation of the intensity of the test stimulus. If contrast increases on account of a decrease in the intensity of background illumination the responses first increase and then remain unchanged. The range of contrasts within which the response is a linear function is narrowed if the intensity of the test stimulus is reduced. Counting the number of spikes in different time intervals of the response (t) showed that the greater the value of t (within the first 70–90 msec of the response) the steeper the curve of the number of spikes as a function of contrast. The Weber-Fechner law applies in the receptive field of the lateral geniculate body. The results are compared with those of some psychophysiological experiments.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 267–274, May–June, 1977.     

Acoustic signal patterns as reflected in the frequency following response of the cat auditory system

In the source of experiments on unanesthetized cats it was shown that all the essential qualities of acoustic stimuli are expressed in the frequency following response (FFR) peculiar to the lower regions of the auditory system (the inferior colliculus included). Amplitude and wave-form of response largely depend on the frequency and intensity of stimulation, frequency and phasic spectra bands for complex signals, together with their wave form and periodicity, acoustic masking of the "useful" signal, and finally interaural differences in stimulation modelling different spatial positions of the sound source.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 67–74, January–February, 1987.     

Responses of auditory medullary units to sinusoidally amplitude-modulated tones in frogs

Spike discharges of medullary units ofRana ridibunda in response to tones of optimal frequency for the neuron, with sinusoidal amplitude modulation, was studied. Reproduction of sound modulation in unit activity was assessed by the use of phase histograms of responses corresponding to the period of modulation. Amplitude modulation was reproduced in the firing pattern of neurons of the dorsal nucleus over a wide range of modulation frequencies and carrier levels. Accentuation of small changes of amplitude for modulation frequencies of 70–150 Hz was observed in many neurons of the superior olives. The phase of the response was a linear function of modulation frequency both in the dorsal nucleus and in the superior olives. The greatest enhancement of amplitude changes corresponded to low modulation indices.Academician N. N. Andreev Acoustics Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 390–396, May–June, 1985.     

Frequency characteristics of skate electroreceptive central neurons responding to electrical and magnetic stimulation

Responses of single neurons in the lateral lobes of the medulla to stimulation of the electroreceptive system by homogeneous sinusoidal electrical and magnetic fields were investigated in acute experiments on the skateRaja radiata. Thresholds of neuronal responses to electrical stimulation varied from 0.03 to 10 µV/cm. The optimal frequency ranges for electrical and magnetic reception were in the regions of 0.05–5 and 2–3 Hz respectively. The possible mechanisms and functional significance of frequency characteristics of central neurons are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. All-Union Cardiologic Scientific Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 464–470, July–August, 1984.     

Modular organization of callosal neurons in the rabbit sensomotor cortex

The density of distribution of callosal neurons in the rabbit sensomotor cortex was studied by injecting horseradish peroxidase into the symmetrical region of the cortex. The degree of inequality of distribution of labeled neurons was determined visually and by statistical analysis. Stained callosal neurons were mainly small and medium-sized pyramidal cells, located chiefly in layer III–IV, and substantially less frequently in layers V and VI. Different forms of grouping of labeled neurons were observed in layer III–IV: two cells at a time, five to eight cells arranged vertically, or in concentrations, whose width was usually 120–200µ, and separated by areas with reduced density. The results are regarded as confirmation of those drawn previously from results of electrophysiological investigations on the modular organization of callosal connections in the rabbit sensomotor cortex.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Brain Institute, Academy of Medical Sciences of the USSR, Moscow. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 451–457, July–August, 1984.     

Functional classification of neurons of the cat inferior colliculus on the basis of temporal characteristics

We investigated the impulse activity of 103 neurons in cats anesthetized with a mixture of chloralose and urethane. The following response characteristics were studied in detail: 1) the latent period of the first impulse as a function of tone intensity; 2) threshold as a function of duration; 3) the frequency-threshold curves under the action of short (1–2 msec) and long (100–200 msec) tones; 4) the discharge "pattern" and the number of impulses under the action of signals with different durations and intensities. We demonstrated that the temporal characteristics of different neurons exhibit substantial differences. The high positive correlation among the temporal characteristics investigated enabled us to distinguish three groups of neurons. The first group was characterized by the following properties: a) short latent periods with a threshold tone intensity; 2) a short summation time (or none at all); 3) similarity of the frequency-threshold curves for short and long signals; 4) an initial on-discharge of 1–3 impulses. The second group was characterized by: 1) long latent periods with a threshold tone intensity; 2) pronounced temporal summation; 3) steeper frequency-threshold curves when the tone duration was increased; 4) prolonged discharge.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 137–146, September–October, 1969.     

Serotonin-induced changes in the action of functionally distinct neurons in Helix pomatia

The effects of serotonin on the amplitude of summated EPSP in interneurons and on the duration of action potentials in sensory neurons, interneurons, and motoneurons involved in avoidance behavior were investigated in functionally distinct neurons isolated from theHelix pomatia nervous system. The duration of action potentials in sensory neurons was found to increase under the effects of serotonin (and this could underly the rise in EPSP amplitude), although that of interneuron and motoneuron spikes did not change. The functional significance of selective neuronal response to a rise in serotonin concentration is discussed, together with the mechanics underlying such effects.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 316–322, May–June, 1987.     

Distribution of directionally selective neurons within the thalamic nuclei and striopallidal complex of the human brain

Spike activity was analyzed in the course of visual testing for directional sensitivity in 177 neuronal populations in different thalamic nuclei and the striopallidal complex in the brain of nine parkinsonian patients, diagnosed and treated using implanted intracerebral electrodes. Directionally selective neurons were discovered in the centrum medianum, the thalamic zona incerta and reticular nucleus, the caudate nucleus, and the central area of the globus pallidus. Proportions and distribution of neurons with different properties were investigated in the thalamic nuclei and striopallidal complex.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 652–660, September–October, 1989.