Correlation between different forms of trace phenomena in the activity of rabbit visual cortex neurons]

Plastic changes in the components of the unit responses in the rabbit visual cortex (VC) in the course of electrical stimulation (with different parameters) of the lateral geniculate body (LGB) were compared with the capacity of the same units for trace driving to the LGB preceding stimulation. Potentiation of inhibition (inhibitory pauses) in reponse to electrical LGB stimulation is the main plastic phenomenon in the activity of VC units. Trace driving is characteristic predominantly of units with enhanced plasticity of the excitatory sign, a tendency toward epileptiform activity after LGB tetanization. In most cases inhibitory reaction is expressed in weakening of the periodic component of neuronal activity corresponding to the frequency of stimulation. The level of trace suppression of periodicity positively correlates with potentiation of the inhibitory pause during prolonged LGB stimulation.     

Dynamics of functional reciprocal connections between cerebral motor cortex neurons under stimulation in cats

Activity was recorded from neurons belonging to the representation of the forelimb in the motor cortex (sulcus cruciatus, L 7–9 mm) using multiple multi-channel/barrel electrodes during acute experiments on cats. Cross-correlation analysis of impulse trains was adopted to investigate dynamics of interneuronal connections during passive flexion and electrical stimulation of the limb contralateral to the recording site. It was found that neither passive bending nor electrical stimulation of the limb leads to a significant increase in the total number of direct relationships between cortical neurons. At the same time, passive flexion does produce a considerable decrease in the number of instances of both inputs operating in neighboring neurons (50–100 µm apart) and an increase in cells located further (between 100 and 400 µm) apart. Some increase in the number of direct inhibitory interactions between neighboring neurons was observed during electrical stimulation.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Nentskii Institute of Experimental Biology, Warsaw, Poland. Center of Experimental and Clinical Medicine, Warsaw, Poland. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 73–80, January–February, 1991.     

The analytical characteristics of the dynamics of interneuronal functional connections during conditioned-reflex activity]

The dynamics of functional relations between neurons was studied in the frontal cortex of dogs performing reversal conditioning task. To reveal the functionally relevant relationships between the temporal patterns of correlated firing and behavioral events, we developed an original processing technique. The technique included the following procedures: a) isolation of the "coupled spikes" (CS) from simultaneously recorded impulse trains: b) search for the temporal patterns of correlated firings and their classification by clustering single trials with similar temporal distribution of CS; c) assessment of behavioral significance of the identified patterns by evaluation of the probabilities of coincidence of behavioral events and different CS patterns. Significant correlations between impulse trains were revealed in 38 neuronal pairs of 456 analyzed. The effects of change in behavioral context on the CS dynamics during the task performance were found in 87% of neuronal pairs with correlated activity. In 17 pairs the behavioral conditions were identified, under which potentially connected neurons fired independently during all the periods of the behavioral task. The potentialities of the advanced processing technique are discussed. We suggest that this analysis can provide useful information about the temporal distribution of correlated firings under conditions of nonstereotyped behavior, when an animal reacts in the dynamically organized experimental context.     

Multivariate EEG spectral analysis evidences the functional link between motor and visual cortex during integrative sensorimotor tasks

The identification of the networks connecting brain areas and the understanding of their role in executing complex tasks is a crucial issue in cognitive neuroscience. In this study, specific visuomotor tasks were devised to reveal the functional network underlying the cooperation process between visual and motor regions. Electroencephalography (EEG) data were recorded from twelve healthy subjects during a combined visuomotor task, which integrated precise grip motor commands with sensory visual feedback (VM). This condition was compared with control tasks involving pure motor action (M), pure visual perception (V) and visuomotor performance without feedback (V + M). Multivariate parametric cross-spectral analysis was applied to ten EEG derivations in each subject to assess changes in the oscillatory activity of the involved cortical regions and quantify their coupling. Spectral decomposition was applied to precisely and objectively determine the power associated with each oscillatory component of the spectrum, while surrogate data analysis was performed to assess the statistical significance of estimated coherence values. A significant decrease of the alpha and/or beta power in EEG spectra with respect to rest values was assumed as indicative of specific cortical area activation during task execution. Indeed alpha band coherence increased in proximity of task-involved areas, while it was suppressed or remained unchanged in other regions, suggesting the activation of a specific network for each task. According to our coherence analysis, a direct link between visual and motor areas was activated during V + M and VM tasks. The effect of visual feedback was evident in the beta band, where the increase of coherence was observed only during the VM task. Multivariate analysis suggested the presence of a functional link between motor and visual cortex subserving sensorimotor integration. Furthermore, network activation was related to the sum of single task (M and V) local effects in the alpha band, and to the presence of visual feedback in the beta band.     

Glutamate dehydrogenase activity in motor cortex neurons during restoration of disrupted visual function]

The recovery of the visual function of rats throughout two weeks after deprivation period (keeping animals in dark chambers for 8 weeks from their birth) leads to a significant normalization of the activity level of glutomatedehydrogenase in the neurones of the III and V layers of the motor cortex. The changes of the enzyme activity in the neurones are accompanied by a diminution of their sizes. The obtained data together with the results of the previous studies (Busnuk, 1976), suggest that the elimination of the visual impulse activity in the early ontogenesis exerts a specific and reversible influence on the morpho-chemical differentiation of neurones both in the visual and in the motor cortical areas. The functional factors determining the direction of changes in the studied parameters of cortical neurones during deprivation and in the rate of their normalization during recovery of the visual function are discussed.     

The temporal organization of the functional connection of the motor cortex neurons in the cat]

Conditioned food-procuring response to time (2 minutes interval) was elaborated in cats, multiunit activity of the motor cortex being recorded. On the basis of single spike trains discriminated from the multiunit activity the cross-correlation histograms were built and the spikes composing their peaks were analysed in real time. This secondary analysis of the histograms allowed to ascertain the dynamics of functional connections between the neurons during the phase of active waiting according to the distribution of coincident impulses. A concentration of coincident impulses of simultaneously recorded cells was observed in different moment of time. In some neuronal pairs the concentration of coincident impulses was revealed to the end of the conditioned interval. The data obtained are considered as a manifestation of the conditioned reaction at the level of neuronal interaction.     

Changes in the dimensions of motor neurons and their components with different forms of nerve center activation]

Experiments in frogs have shown that a prolonged orthodromic rhythmical activation of motoneurons induce changes in their size and staining. Under these conditions the size of all components of motoneurons (cytoplasm, nucleus, nucleolus) is changed. The cytoplasm size changes are more pronounced than those of the nucleus. Under prolongation of the low frequency stimulation (1 per sec.) of the dorsal roots the changes are of phasic character: an initial enlargement (10 minute-long stimulation) and a subsequent decrease of all the above spinal cord motoneuron components (25 minute stimulation). After the 10 minute high frequency stimulation (50 impulses per second) of nerve centers there occur a sharp decrease of the size of the cytoplasm and the nucleus.     

Correlations between the properties of visual cortex neurons in the cat

In acute experiments on immobilized cats 13 functional characteristics of 96 visual cortex neurons were investigated. By means of regression, cluster, and multivariate analyses, these could be divided into two subgroups with varying degrees of correlatedness. Cells of the first subgroup were more frequently characterized by their relatively central location in the visual receptive field, while those of the second subgroup were more often found at the periphery. A significant correlation was found between 11 of the properties investigated. In each subgroup, cells with more centrally localized small receptive fields had, in comparison with neurons of the peripheral visual projection, short latent periods, lower thresholds, phasic response, and brief summation; their responses varied widely in intensity, and they had greater differential sensitivity, and were distinguished by high-frequency discharges. Significant correlation coefficients between the factors studied fluctuated between 0.21 and 0.99; moreover, there were almost twice as many significant relationships in the first subgroup of neurons as in the second. The possible mechanisms of correlations between the properties of the visual cortex neurons are discussed, as well as the reasons why they differ in cells of the two subgroups, the cortex, and the lateral geniculate body.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 587–596, September–October, 1985.     

Activity of anterolateral motor cortex neurons in instumental food-acquisition and alcohol-acquisition behavior

Singleunit activity of anterolateral area of motor cortex in rabbits subjected to chronic ethanol treatment was recorded to study interconnections of neuronal mechanisms of newly formed instrumental alcohol-acquisition behavior (IAB) and previously formed food-acquisition behavior (IFB). Adult animals were trained to perform IFB in experimental cage equipped with two food boxes and two pedals situated in the corners of the cage. Food was presented automatically in a food box after the pressing of an appropriate pedal. Same rabbits after 9 mo. of chronic alcohol treatment were trained to perform IAB in the same experimental cage (gelatin capsules filled with 15% ethanol solution were placed into the food box instead of food). Activity of 121 units of anterolateral area of motor cortex was studied. Each unit discharges were analysed in IAB as well as in IFB. The data obtained testifies that neuronal sets subserving IAB and IFB overlap but not completely. 44 "common" neurons permanently activated in both behaviors and 3 neurons specifically activated in each of behaviors (one in IAB and two in IFB) were found. We consider the formation of IAB as systemogenesis that is related to the consolidation processes: the formation of new neuronal specializations and to the accommodative re-consolidation: modification of early specialized cells ("common"). It is shown in the Discussion that present experiments help us not only understand interconnections of neuronal mechanisms of newly formed IAB and early formed IFB but also provide an additional insight into the nature of similarity between neuronal mechanisms of long-term memory and long-lived modifications resulting from repeated drug exposure.     

The functional role of octopaminergic neurons in insect motor behavior

The role of efferent, octopaminergic dorsal unpaired median (DUM) neurons in insects is examined by recording from them during motor behaviour. This population of neuromodulatory neurons is divided into sub-populations which are specifically activated or inhibited during ongoing motor behavior. These neurons are always activated in parallel to the respective motor circuits, and in addition to their modulatory effects on synaptic transmission may also cause metabolic changes in their target tissues.     

The topography of functional interhemispheric asymmetry in the visual cortex]

Functional interhemispheric asymmetry was investigated by evoked potentials method in experiments on ten cats under ethaminal anaesthesia at 200 points of the visual cortex during the action of binocular and monocular photic flashes of submaximal intensity. Topographic maps have been plotted of the functional interhemispheric asymmetry. In most of the animals a hemisphere dominant and non-dominant at the given moment can be singled out. Section of the callosal body leads to reduction of the functional interhemispheric asymmetry due to a decrease of the focus of maximum activity in the dominant hemisphere and its increase in the non-dominant one. A mozaic pattern of functional interhemispheric asymmetry has been demonstrated, as expressed in the existence of zones of inverse dominance along with prevailing zones of direct dominance. Section of the callosal body produced a decrease in the area of direct dominance and an increase in that of inverse dominance. Absolute interhemispheric asymmetry was most pronounced in the central part of the visual cortex (field 18 and its medial boundary) and the relative one, on the periphery of the visual area (fields 17 and 19).     

Arrangement and afferent connections of the neurons in the visual cortex differing in the size of the receptive fields

In the area 17 of the cerebral cortex of guinea pigs cells with small and medial receptive fields (RF) are concentrated at the sites of separate groupings of neurons excited by flashes of diffusion light. There are also cells with large RF here. At such sites of the cortex when specific afferents are electrically stimulated many cells exhibit monosynaptic activation irrespective of their RF size. The main part of the neurons with large RF is situated in the areas of the cortex between the excited grouping and monosynaptical excitation is not inherent in such neurons. Most cells of these areas are not excited by specific afferents.     

Specification of synaptic connections between sensory and motor neurons in the developing spinal cord

Experimental studies of mechanisms underlying the specification of synaptic connections in the monosynaptic stretch reflex of frogs and chicks are described. Sensory neurons innervating the triceps brachii muscles of bullfrogs are born throughout the period of sensory neurogenesis and do not appear to be related clonally. Instead, the peripheral targets of these sensory neurons play a major role in determining their central connections with motoneurons. Developing thoracic sensory neurons made to project to novel targets in the forelimb project into the brachial spinal cord, which they normally never do. Moreover, these foreign sensory neurons make monosynaptic excitatory connections with the now functionally appropriate brachial motoneurons. Normal patterns of neuronal activity are not necessary for the formation of specific central connections. Neuromuscular blockade of developing chick embryos with curare during the period of synaptogenesis still results in the formation of correct sensory-motor connections. Competitive interactions among the afferent fibers also do not seem to be important in this process. When the number of sensory neurons projecting to the forelimb is drastically reduced during development, each afferent still makes central connections of the same strength and specificity as normal. These results are discussed with reference to the development of retinal ganglion cells and their projections to the brain. Although many aspects of the two systems are similar, patterned neural activity appears to play a much more important role in the development of the visual pathway than in the spinal reflex pathway described here.     

Biochemical differences in the reactions of visual cortex neurons to deprivation]

Early visual deprivation was interferometrically shown to entail changes in the concentration and contents of the protein substance with simultaneous changes of the neurons size. The changes are statistically significant in the lamina V and not in the laminasIII and IV. The changes in each lamina are associated with definite group of the neurons the development of which is, probably, determined by visual stimuli.     

Centrifugal and centripetal connections of the cat visual cortex

In experiments on curarized cats unit responses in the dorsal lateral geniculate body to stimulation of various zones in area 17 of the visual cortex were analyzed. Of all cells tested 69% were found to respond antidromically and 8% orthodromically; in 7.6% of cells IPSPs occurred either after an initial antidromic spike or without it. The velocities of conduction of excitation along the corticopetal fibers of the optic radiation varied from 28 to 4.3 m/sec, but the three commonest groups of fibers had conduction velocities of 28–19, 14–12, and 10–9.5 m/sec. A difference between latent periods of antidromic responses of the same neurons was found to stimulation of different zones of the visual cortex; this indicates that axons of geniculo-cortical fibers split into several branches which form contacts with several neurons in area 17 of the visual cortex. The degree and possible mechanisms of cortical influences on neurons of the lateral geniculate body are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 243–249, May–June, 1976.