Electrical characteristics of neurons in the cat motor cortex

Electrical characteristics of motor cortical neurons were studied in acute experiments on immobilized cats. Values of the input resistances varied from units to tens of megohms (mean 11.11±3.93 MΩ). The threshold current is a hyperbolic function of input resistance of the corresponding neurons and negative correlation was found between the axonal conduction velocity and input resistance. The time constant (τ₀) of the membrane was 7.1±3.46 msec. A time constant τ₁, of 1.65±0.36 msec, could also be distinguished in some neurons. Electrotonic lengths of dendrites of the cortical neurons were calculated by the use of Rall's model: mean 3.66±0.94 (in units of length constant).     

The effect of acetylcholine and atropine on the temporal connection in the neuronal populations of the motor cortex]

On alert non-immobilized rabbits the activity of neurones in the sensorimotor cortex was studied at pair combination of brain structures stimulations. During omission of the reinforcing stimulus at the place of its expected presentation a complicated complex develops of neurones impulses reconstructions, consisting in reproduction of responses and activity changes which by their configuration differ from them and usually appear in later terms. Direct acetylcholine application on the cortex promotes manifestation of both types of neurones activity reconstructions. But atropine application depresses mainly the second type of reconstructions. Besides, acetylcholine increases the general duration of the given conditioned effects, but atropine decreases it.     

The temporal organization of human fetal motor function]

Fetal motor bursts were recorded in pregnant women at 11-18, 20-24 and 30-32 weeks of pregnancy. It was stated that spontaneous motor activity in human fetus is similar to autogenic periodic motor excitation observed in other species of vertebrates, i.e. presence of the main rest-activity circles with a period near 1 minute, the existence of rhythmic components with 6-8-second intervals during active phases and decreasing of quantity of excitation bursts with age.     

Changes in the dendritic organization of the neurons of the isolated visual cortex of the cat]

The cortex of one hemisphere in cats was isolated according to M.M. Khananashwili method by means of surgical section of its projection fibres which connect it with subcortical structures. In five cats of means of Nissl's method the neuronal status of different cortical layers in the field 17 was studied during long postoperative terms (from 9 months up to 2 years). In 9 cats the neurons of the same field were impregnated after Golgi-Bubenett method and studied during the same postoperative terms. Cytological investigation in the majority of neurons did not reveal any pathologic changes during different postoperative terms up to one year. In two years, slight neuronal changes were noted presented in poor staining and vacuolization of cytoplasm. As a result of deafferentation performed shortening and thickness of dendritic branching was noted, as well as decrease in the number of thorns of large pyramids in layers III, IV, and V of the isolated cortex. Dendrites and thorns in small and medium-sized pyramids in layers II, III, IV, V, and VI were preserved to a great extent. It is possible to conclude, on the fact of thorns preserving in the major number of the neurons, that the neocortex possesses an enormous intracortical connective system that is responsible for the high degree of functional neuronal activity in the isolated cortex.     

Investigation of habituation reaction of neurons of the cat motor cortex

The neuronal and total surface activity of the cortical representation of the motor analyzer in the region of the posterior sigmoid gyrus of the cat brain in response to rhythmical light, sound, and electrical stimuli and their complexes was analyzed. Two groups of neurons were found, of which the first is characterized by a gradual decrease in the number of peaks in the response and by their subsequent disappearance and the second by the absence of a discharge in response to stimulation and by its development before the application of the next stimulus. The first group was comprised of neurons which do not have background activity and the second was made up of neurons with a background activity of 0.4–3.7 imp/sec. This reorganization of the activity of cortical neurons in response to rhythmical stimulation is considered to be a habituation phenomenon.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 245–251, May–June, 1971.     

Investigation of functional organization of receptive fields in the cat visual cortex

Receptive fields of neurons in Area 17 of the visual cortex were investigated in cats. Concentrically shaped fields, fields responding selectively to orientation of a strip or edge, and fields which can be regarded as intermediate between the first two types are described. The boundary between zones of summation and of lateral inhibition coincides in some receptive fields with the boundary between central and peripheral zones with opposite forms of response, while in other fields they do not coincide. For some cells there is no peripheral zone or it may disappear with worsening of the state of function. Cells were observed for which an increase in area of the stimulus in the central zone inhibits the response reaction. Analysis of these data suggests that several cells of the geniculate ganglion converge on some cortical neurons, and several cortical cells on others. An effect of adaptive inhibition was found in which constant illumination of an area in the center of the receptive field inhibits the response in another part. It is shown that this effect is unconnected with the action of scattered light. Constant illumination of the peripheral part of the receptive field deinhibits adaptive inhibition. The boundary between the zones of summation and of lateral inhibition coincides with the boundary between the zones of adaptive inhibition and deinhibition.I. V. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 90–100, July–August, 1969.     

Functional organization of afferent inputs of neurons of the cat somatic cortex

Responses of cortical neurons in the posterior sigmoid gyrus to stimulation of two points of the ventro-posterolateral nucleus were investigated in cats immobilized with D-tubocurarine. Some neurons responding to stimulation of one point of this nucleus with a latent period of 2.5–4 msec, were activated by stimulation of the other point after 10 msec or longer. Conditioning stimulation of one point facilitated or inhibited the response to test stimulation of the other point. The facilitatory effect was usually exhibited if the response latency exceeded 5 msec. It is concluded that a cortical input neuron for some afferent fibers is activated by other similar afferent fibers only after intracortical relay. The system of "input" cortical neurons is thus not only a structural, but also to some extent a functional, concept; under certain conditions an incoming afferent volley activates them only polysynaptically.     

Neuronal organization of field 4 of the motor cortex of the cat brain

By means of the silver nitrate impregnation method after Golgi-Kopsch in kittens and young cats the field 4 in the cerebral motor cortex has been studied. The motor cortex of the field 4 possesses certain heteromorphism. Besides usual stellate and pyramidal neurons, that differ from real ones by some morphological signs: their body is often round, the apical dendrite is much thinner than the corresponding dendrite of a pyramidal neuron, it does not produce oblique branches along the course, never gets into the I layer, the spines arrange less densely. According to the mode of dendrites setting off, the atypical pyramidal neurons can be divided into multipolar and spindle-like with horizontal or vertical branching of the dendrites. According to the spines distribution, the multipolar atypical neurons can be divided into spinous, rare-spinous and aspinous. With respect to various cellular forms and distribution of various types of neurons in layers, every of the areas (gamma, alpha, sfu, fu) possesses specific peculiarities. The greatest variability of the neurons have the field 4 gamma and 4 alpha, where, besides stellate and pyramidal, atypical neurons can be found. The stellate neurons of the field 4 gamma are characterized with a deep arrangement, their number is essentially less, than in other areas of the field 4. In the field 4 alpha they are situated in the layers II-III. Suprafundal and fundal parts of the field do not possess pyramidal atypical neurons and are characterized with presence of large amount of the stellate neurons. In respect to the axonal branching in the suprafundal part of the field 4, 2 types of the stellate cells are distinguished.     

Microelectrode recording of responses in visually observed neurons of the cat motor cortex

With a contact optical system it is possible to carry out intravital studies of neurons and other structures, stained with vital dyes in reflected light in a specially prepared specimen of the cat cerebral cortex. The high-quality characteristics of the optical system used have made combined morphological and intracellular electrophysiological investigations of these neurons possible. The nature of intravital morphological changes in cortical neurons was established in response to their puncture by microelectrodes with tips with different external diameters and configurations; certain morpho-functional correlations were found in the response of pyramidal neurons to disturbance of their temperature regime.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 122–125, March–April, 1976.     

Afferent inhibition and functional properties of neurons in the vibrissae projection area of the cat somatosensory cortex]

The aim of this study was to investigate the role of inhibitory processes in S-1 cortex of cats. The inhibition was evoked by "natural" afferent stimulation of the fascial vibrissae. For this purpose, two neighboring vibrissae were sequentially stimulated by mechanical deflection; single unit activity was recorded simultaneously from the cortex. Results showed that conditioning by afferent stimulation significantly influenced the directional sensitivity of cortical neurons. These data and analysis of spatial pattern of stimulated vibrissa indicate that detector neurons could be quickly modified during sensory processing.     

The assessment of the strength of the interaction between neurons of the cat motor cortex in a conditioned reflex to time]

The work was conducted on cats with recording multineuronal activity of the motor cortex at the elaboration of conditioned reflex to time. Strength of interaction was estimated between the adjacent and remote neurones in the limits of 0.5 m. The dynamics of strengths of interneuronal interaction in most cases did not correlate with the dynamics of impulses frequency of the studied neurones. Changes of strengths of interaction between mutually remote neurones at CRT were met more frequently than between the adjacent ones, what may serve as one more evidence of the hypothesis on more strict structure of connections within microsystems and greater plasticity of connections between microsystems.     

Sensory input to neurons of the motor projection of biceps in the cat cortex

Correlation of cortical unit activity in the motor area for the biceps muscle was studied in chronic experiments on cats. In a group of neurons whose activity correlated with movement 68.1% of units had no sensory input from the working limb whereas in a group of neurons not correlating with movement there were 97.6% such units. In 24.2% of group I neurons cutaneous receptive fields of activation type were discovered on the distal part of the dorsal surface of the working limb. Five neurons responding to sensory input from the joints of the working limb were studied in this group.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 563–569, November–December, 1977.     

Interaction of direct afferent and recurrent signals in cat motor cortex neurons

Intracellular activity was recorded from the functionally identified motor cortex neurons (MI, area 4) in acute experiments on myorelaxin-immobilized cats under calypsol anesthesia. Changes in neuronal responses to testing stimulation of the ventrolateral thalamic nucleus or pyramidal tract fibers were studied; the same or another input was used for a conditioning stimulation. Excitatory and inhibitory components of test responses of variousMI neurons were found to be either facilitated or depressed. The facilitation of orthodromic excitation was more frequent in the case of thalamic testing stimulation. The depression of both excitatory and inhibitory components of the response was more pronounced with paired stimulation of the pyramidal tract fibers. The peculiarities of interaction between direct afferent and recurrent signals in theMI neurons are thought to be determined by different distribution of thalamocortical fiber terminals and recurrent collaterals of corticofugal axons in the cortex and nonuniform localization of their synapses on dendrites and somata of the studied cells. It seems possible that these peculiarities also are connected with different chemical mechanisms of synaptic transmission in the above synapses and different properties of postsynaptic membrane receptors.Neirofiziologiya/Neurophysiology, Vol. 26, No. 3, pp. 203–210, May–June, 1994.     

The neuronal organization of a focus of conditioned excitation in the cat sensory-motor cortex]

The activity of single units in the focus of conditioned excitation was studied during defensive conditioning to direct electrical stimulation of the cat sensorimotor cortex. Reorganizations of spike activity set in during the period of reflex elaboration, were manifest in the increased number of excited neurones and those which respond both to the conditioned and unconditioned stimuli. In the course of elaboration, the inhibitory phase of unit responses to direct electrical stimulation of the sensorimotor cortex was reduced, while the frequency of background unit spike activity was enhanced. Acute extinction of the reflex restored the initial duration of the inhibitory phase and reduced the frequency of the background activity.     

The functional organization of the barrel cortex

The tactile somatosensory pathway from whisker to cortex in rodents provides a well-defined system for exploring the link between molecular mechanisms, synaptic circuits, and behavior. The primary somatosensory cortex has an exquisite somatotopic map where each individual whisker is represented in a discrete anatomical unit, the "barrel," allowing precise delineation of functional organization, development, and plasticity. Sensory information is actively acquired in awake behaving rodents and processed differently within the barrel map depending upon whisker-related behavior. The prominence of state-dependent cortical sensory processing is likely to be crucial in our understanding of active sensory perception, experience-dependent plasticity and learning.     

Distribution of inhibitory synapses on the somata of pyramidal neurons in cat motor cortex

The mechanisms by which cortical neurons perform spatial and temporal integration of synaptic inputs are dependent, in large part, on the numbers, types, and distributions of their synapses. To further our understanding of these integrative mechanisms, we examined the distribution of synapses on identified classes of cortical neurons. Pyramidal cells in the cat motor cortex projecting either to the ipsilateral somatosensory cortex or to the spinal cord were labeled by the retrograde transport of horseradish peroxidase. Entire soma of selected corticocortical and corticospinal cells were examined using serial-section electron microscopy. The profiles of these somata and the synapses formed with each of these profiles were reconstructed from each thin section with a computer-aided morphometry system. All somatic synapses were of the symmetrical, presumably inhibitory type. For both cell types, these synapses were not homogeneously distributed over the somatic membrane, but were clustered at several discrete zones. The number and density of synapses on the somata of different corticocortical and corticospinal neurons were not significantly different. However, the density of these synapses was inversely correlated with the size of their postsynaptic somata. We discuss the significance of these findings to the integrative properties of cortical neurons.