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T M Zagorul'ko

Publications and source records attributed to T M Zagorul'ko.

At least 19 recordsLinked to original sources
PubMed1984

[New electrophysiologic data on localizing visual representation in the limbic area of the neocortex].

In the limbic part of the rat neocortex, afferents from the retino-geniculo-cortical and retino-tecto-thalamo-cortical visual subsystems converge to the area 29. A specific feature of the area 29 responses to stimulation of thalamic visual nuclei (the LGB and the postero-lateral nucleus) involves gradualness of their appearance during rhythmic stimulation. The responses have an initial negative phase, are resistant against nembutal, have a short and stable latency, their neuronal reaction being phasic in nature and showing dependence on physical parameters of stimulation. These intermediate type reactions possess features of both specific and unspecific responses of the neocortex which seems to be characteristic of the area 29 function.

Afferent Pathways↗
PubMed1980

[Afferent supply to the most ancient visual area of the neocortex, field 29 of the limbic cortex].

In white anesthetized rats electric stimulation of n. anterodorsalis and light stimulation evoked potentials in the retrosplenial cortex, field 29. The EPs were surface-negative, multicomponent, their latency at the n. anterodorsalis stimulation being 5.1 +/- 0.6 (with a range of 2-7) msec, at the light stimulation -- 21 +/- 1.7 (with range of 15-30) msec. The EPs in the field 29 at low-frequency rhythmic light stimulation and at n. anterodorsalis stimulation (1-5/sec) revealed the phenomenon of habituation and driving. The layer analysis of the light EPs showed reversal of polarity in the upper part of layer V of the cortex, while after n. anterodorsalis stimulation the reversal of polarity occurred beneath the layer VI. The possibility of existence of several thalamis visual inputs in the field 29, is discussed.

Animals↗
PubMed1976

[Tecto-cortical connections in the rat visual system].

Electric stimulation of the colliculus superior evokes potentials (EP) in the visual cortex of the ipsilateral hemisphere of the rat brain, their localization coinciding with the zone of flash-evoked potentials. EPs of maximal amplitude were observed during stimulation of the central layers of the colliculus superior. Short latency of the EPs (3.2 +/- 1.1 msec; p less than 0.05) and the relevant morphological data suggest a single relay in rat's tecto-cortical visual system. The data are discussed in regard to the comparative telecephalisation of the retino-tectal system in submammalian vertebrates and in mammals.

Animals↗
PubMed1975

[Corticalization of 2 regions of the visual system in the evolution of vertebrates].

Data on the evolution of the visual system in the phylogenetic scale of vertebrates are reported. Visual projections in the telencephalon of cyclostomes (lampreys) and retinothalamo-telencephalic channel in elasmobranches (skates) are shown. In amphibians (frogs) and reptiles (turtles) the existence of two visual subsystems (retino-thalamo-telencephalic and retino-tecto-thalamo-telencephalic) is determined, both being overlapped partially at the level of n. geniculatus lateralis and totally in the telencephalon. In turtles earlier visual and tectal impulses towards the telencephalon proved to be relayed in n. geniculatus lateralis and later ones--in n. rotundus. In mammals (rats) visual tecto-cortical connections are shown to have one synaptic relay in thalamic structures since cortical potentials evoked by stimulation of the colliculus superior in rats posses a rather short latency. Significant latency shortening of tectal visual responses in monkeys, as compared with the latency of the respective potentials in turtles (chronic identical experiments), supports the idea of the progressive development of the tectal division of the visual system in the vertebrate phylogony. It is concluded that both divisions of the visual system--retino-thalamic and retino-tectal underwent corticalization at earlier evolutionary stages.

Animals↗
PubMedDate not supplied

Tectocortical connections in the rat visual system.

Electrical stimulation of the superior colliculus by square pulses evokes responses in the ipsilateral occipital region whose localization coincides with the zone of evoked potentials to photic stimulation. The short latent period of the visual cortical evoked potentials to stimulation of the superior colliculus (mean 3.2 +/- 1.1 msec; P less than 0.05) together with morphological data suggests that only one relay, in the structures of the thalamus, occurs along the tectocortical pathway in the rat visual system. In the poorly differentiated cortex of the rat no separate representation of retino-geniculo-cortical and tectocortical channels could be found.

Animals↗
PubMedDate not supplied

Comparison of electrophysiological characteristics of the retino-collicular and retino-thalamo-cortical parts of the visual system of the monkey Macaca rhesus.

In chronic experiments and in acute experiments with nembutal narcosis, photic-driven evoked potentials (EP's) were studied in the superior colliculi (SC) and in the cerebral visual cortex (VC, Area 17). In chronic experiments it was found that the EP's in SC and VC have similar latency periods (LP's) equal, respectively, to 12 +/- 1 and 12 +/- 2 msec (p less than 0.05); refractory periods during application of paired flashes are 50 and 70 msec for SC and VC, respectively. The critical frequencies for imitation of rhythmic flashes in both visual centers also coincide, reaching 20-25/sec. EP's with short LP's, equal to the LP's of evoked potentials in the VC, were found also in the frontal and motor cortex and the hippocampus. The problem regarding telencephalization of the retino-tectal channel of the visual system is discussed.

Animals↗
PubMedDate not supplied

[Differences in the sensory support of the anterior and posterior sections of the limbic cortex of the rat].

Using retrograde axonal transport of horseradish peroxidase, studies have been made on the thalamic projections in the anterior and posterior parts of the limbic cortex with special reference to exterosensory system projections (visual, auditory and somatic). Projections of the retinorecipient nuclei of the anterior hypothalamus and classic thalamic visual relays (n. geniculatus lateralis dorsalis, n. lateralis posterior, pretectum) were found in the anterior and posterior limbic cortex. There are also inputs from the thalamic relays of the auditory (n. geniculatus medialis) and somatic (n. ventralis posterior) systems in the posterior limbic cortex The data obtained indicate: 1) that sensory supply of the limbic cortex in rats may be realized via direct pathways from sensory thalamic relays; 2) that thalamic sensory supply of the anterior limbic cortex differs from that of the posterior one. In the former, projections of the thalamic relays of the visual, auditory and somatic systems were found, whereas in the posterior cortex only visual system is presented. Topographic organization of the thalamic nuclear areas sending afferents to the anterior limbic cortex differs from that of the posterior limbic cortex.

Animals↗
PubMedDate not supplied

[Cortical representation of nonclassical parts of the visual system].

Cortical evoked potentials and extracellular evoked neuronal activity have been investigated in unanesthetized d-curarine immobilized rats during stimulation of the superior colliculi. The focus of responses was found in the lateral part of the visual neocortex (area 18a according to Krieg [5]). The evoked potential includes a negative and subsequent positive waves, its latency being equal to 7.9 +/- 2.8 msec. With deepening the electrode the amplitude of the response decreases, although its polarity remains unchanged. The neuronal activity is of phasic character. During simultaneous record of the evoked potentials and neuronal activity, temporal correlation between impulse activity and the ascending part of the main negative wave of the EP is observed. The data obtained indicate imcomplete overlapping of the retino-geniculo-cortical and retino-tecto-thalamo-cortical channels in the visual system of rats.

Animals↗
PubMedDate not supplied

[Study of the ancient tecto-thalamo-cortical pathway of the visual system in rats].

Recording the evoked potentials and neuronal activity, electrophysiological studies have been made on tecto-thalamo-cortical tract in rats. The existence of a system of efferent projections in the superficial, visual layers of the superior colliculi was shown which are diffusely present in the nucleus lateralis posterior (n. LP), indicating low level of morpho-functional organization of this region of the dorsal thalamus in rats. In response to electrical stimulation of the n. LP, in laterocaudal parts of the visual system (fields 17 and 18a of the cortex) the evoked potentials of primary-negative polarity were observed which are associated mainly with the superficial (I--IV) cortical layers. Predominant representation of tecto-thalamo-cortical system in the laterocaudal visual area of the cortex indicates the tendency to separate representation (with respect to cortical areas and cortical layers) of retino-geniculate and retino-tecal visual systems in rats.

Animals↗
PubMedDate not supplied

[Comparison of the electrophysiologic characteristics of retino-collicular and retino-thalamo-cortical divisions of the visual system of Macaca rhesus monkeys].

In chronic and acute experiments under nembutal anaesthesia, studies have been made on the evoked potentials (EP) elicited by light stimuli in the colliculus superior and in the visual cortex (area 17). It was found that under chronic experiments the EP in the colliculus superior and visual cortex exhibit close (12 +/- 1 and 12 +/- 2 msec. respectively) latent periods; refractory periods determined by paired flashes for both of the parts are equal to 50--70 msec. Critical frequency for EP reproduction of rhythmic flashes in both visual centers is also identical, reaching 20--25/sec. EP with a short latent period equal to that of the EP in the visual cortex were also detected in the frontal and motor cortex, as well as in the hippocamp. The problem of telencephalization of the retinotectal path of the visual system is discussed.

Animals↗