Mechanisms of interaction between the parietal association and projection areas of the cat neocortex

Changes in evoked potentials in the first visual (VI), first somatic (SI), and parietal areas of the cortex during local cooling of each area were investigated under pentobarbital anesthesia. Two types of interaction were distinguished. Type I interaction was found in all areas in the early stages of local cooling and was reflected in a similar decrease in amplitude of evoked potentials in intact parts of the cortex. In the thalamic association nuclei — the pulvinar and posterolateral nucleus — somatic evoked potentials were unchanged but visual were transformed differently from those in the cortex. Type IIinteraction was found in the later stages of cooling and only between the association area and each of the projection areas. It was reflected in a greater change in amplitude of the evoked potentials and also in their configuration. In response to somatic stimulation in the early stage of type II interaction transformation of evoked potentials in the cortex took place sooner than in the nuclei; in the later stage it took place immediately after transformation of the "subcortical" evoked potentials. In response to photic stimulation transformations of cortical evoked potentials were always preceded by the corresponding transformations in the nuclei. It is suggested that type I interaction is formed by intercortical connections and type II by direct and subcortical relay connections. Differences in the role of the association area in interaction of types I and II when activated by stimuli of different modalities are discussed.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 573–581, November–December, 1978.     

Distribution of specific signals of different modality in the associative parietal area of the cat cortex

In cats under nembutal anesthesia eliciting specific early components of association responses, the drug parietal distribution upon forepaw and thalamic stimulation was studied: relay somatic-ventrobasal complex (VB) and association nuclei, transmitting specific visual impulses in pulvinar (Pul) and lateral-posterior (LP) areas. Signals of maximum intensity were observed in response to peripheral and central stimulation near somatic area and in response to Pul and LP stimulation in the medial part of parietal cortex. Besides, a general principle revealing more intensive signals of different modality in the areas near lateral sulcus than in other parietal areas was established. The difference in processing of specific polysensory signals in various parietal areas and consequently, different involvement of the latter into the systemic action of the brain was proved, this being related to the character of topical organization of these signals.     

Sexual differences in the interhemispheric asymmetry of the transcallosal responses of the associative areas in the cat neocortex

Sex differences of hemisphere asymmetry of homo- and heterotopic transcallosal responses in association cortex of 48 cats (24 male and 24 female) immobilized by tubocurarine have been studied by means of topographic EPs recordings in both hemispheres. In males left hemisphere dominates by the amplitude of homotopic and positive wave of heterotopic EPs and right hemisphere dominates by the amplitude of negative wave of heterotopic sensorimotor cortex EPs. The individual asymmetry of EPs has been observed in sensomotor cortex of females and in parietal cortex of animals of both sex. The interhemispheric asymmetry is expressed distinctly in females than in males. It is concluded that sex dimorphism is present in functional organization of associative system of (callosal and intracortical) connections in cat's neocortex projection and association areas which means its more expressed hemisphere lateralization in males with more expressed interhemispheric asymmetry of functional transcallosal connections in females.     

Choline acetyltransferase-containing neurons in the human parietal neocortex

A number of immunocytochemical studies have indicated the presence of cholinergic neurons in the cerebral cortex of various species of mammals. Whether such cholinergic neurons in the human cerebral cortex are exclusively of subcortical origin is still debated. In this immunocytochemical study, the existence of cortical cholinergic neurons was investigated on surgical samples of human parietal association neocortex using a highly specific monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine biosynthesising enzyme. ChAT immunoreactivity was detected in a subpopulation of neurons located in layers II and III. These were small or medium-sized pyramidal neurons which showed cytoplasmic immunoreactivity in the perikarya and processes, often in close association to blood microvessels. This study, providing demonstration of ChAT neurons in the human parietal neocortex, strongly supports the existence of intrinsic cholinergic innervation of the human neocortex. It is likely that these neurons contribute to the cholinergic innervation of the intracortical microvessels.     

Synaptic organization of the cat parietal association cortex (area 5b)

An electron microscopy study was made of synaptic organization in the cat association cortex, area 5b. A total of 1635 axonal terminals were discovered over 6215 µm² (240 electronic imagings of slices of different association cortex layers); i.e., an average of 263±16 terminals per 1000 µm² expanse. It was found that 75.5% of axon terminals contained synaptic vesicles and formed either one- or two-sided contact with postsynaptic structures; 24.5% of axonal terminals contained synaptic vesicles but formed no distinct synaptic contacts with nearby neurons; 84.9% of terminals contained round-shaped or slightly oval synaptic vesicles; 7.8% had both rounded and elongated shapes, and vesicles were very elongated in the remaining 7.3%. Of the axonal terminals having synaptic contacts, axo(dendritic)-spinal terminals accounted for 46.6%, and axodendritic and axosomatic endings amounted to 50.0% and 3.4% respectively (in all 77% of axosomatic terminals contained elongated vesicles and maintained symmetrical contact, while 23% had round-shaped vesicles and formed asymmetrical contact). Calculations show that for each 1 mm³ an average of 258 million axonal terminals are found forming synaptic contacts in the cat association cortex as well as 84 million terminals containing synaptic vesicles but not forming contact.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 174–185, March–April, 1989.     

Functional organization of local neuronal networks in the cat neocortex. Dependence on the food motivation

The multiple unit activity (MUA) from clusters of adjacent neurones in deep layers of the frontal and motor cortex was recorded in alert cats with different levels of alimentary motivation. Up to 7 spike trains were selected from the MUA. Neurones in the local circuits could be divided into 2 groups: large neurones with prevailing divergent characteristics, and small neurones with prevailing convergent characteristics. A 24-hour food deprivation altered the cross-correlation interneuronal connections with a time delay within the range of 2 to 100 ms.     

Effect of electric stimulation of the locus coeruleus on transcallosal response in parietal associative cortex of the cat brain

The influence of conditioning locus coeruleus (LC) stimulation on various components of transcallosal field response was investigated in the parietal cortex of the cat brain. Conditioning LC simulation caused a decrease in fast positive wave amplitude and facilitated slow negative wave. It is concluded that LC suppresses excitatory and facilitates inhibitor processes evoked in the parietal cortex by transcallosal stimulation.     

Microelectrode analysis of neuronal organization of the parietal association cortex

Responses of 304 neurons in the anterior part of the middle suprasylvian gyrus in cats to acoustic, photic, and somatosensory stimulation and also to simultaneous presentation of 2 or 3 stimuli of these modalities. Three groups of neurons were distinguished: those responding by an increased firing rate (187) or by inhibition (22) and those not responding (95). The first group comprised mono- (64) and polysensory (105) and well as neurons responding only to a combination (18). On the basis of the convergent properties of the polysensory neurons in this region it is postulated that the parietal cortex performs principally integrative processes based on iteraction of visual-cutaneous and cutaneo-auditory afferent information.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 4 No. 1, pp. 54–60, January–February, 1972.     

Systems organization of cerebral processes in the cat during learning while undergoing electrical stimulation of the neocortex

A delayed spatial choice (DSC) was elaborated in five cats during electrical stimulation (ES) of the frontal cortical parts with a frequency of 80 imp/s. Then the task fulfillment was tested following cessation of the electrostimulation or under the action of other current frequencies (35,3 and 120 imp/s). The number of erroneous choices increased in the absence of ES or during 3 imp/s ES of the frontal parts. The effects of frequencies of 35,80 and 120 imp/s did not differ. Three cats were trained to DSC without ES. The conditioned reflexes were tested during ES of the frontal cortical parts with current frequency of 3 and 80 imp/s. Statistically significant increase of the number of erroneous responses took place in both situations. The obtained data are discussed from the point of view of the integrative activity of the cerebral structures in DSC. Its disturbance during ES of the cortical zones and dissociation (discordance) after cancellation of stimulation during which the conditioned reflex had been elaborated, point to systemic organization of brain functioning in goal-directed forms of behaviour.     

Organization of afferent inputs of the parietal association (area 7) and Clare-Bishop areas of the cat neocortex

Unit activity was recorded from two parietal areas of the cat neocortex in semichronic experiments. Cell responses to presentation of adequate stimuli of different modalities and to direct electrical stimulation of various cortical zones were studied. About 4% of neurons of the Clare-Bishop area did not respond to visual stimulation. Cells responding to stimuli of different modalities were found in the Clare-Bishop area. A high percentage of cells in this area responded to direct electrical stimulation of area 17. In the association area (area 7) 27% of neurons tested responded to visual stimuli, but only a very small relative number of cells (compared with responding neurons of the Clare-Bishop area) responded to stimulation of the primary sensory areas. Electrical stimulation of area 7 inhibited evoked and spontaneous unit activity in the Clare-Bishop area. The hypothesis that these areas are the association representation of two different sections of the visual system — retino-geniculocortical and retino-tecto-thalamocortical — is discussed.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 612–620, November–December, 1981.