[Physiological Aspects of the Application of Hodgkin-Huxley Model of Action Potential Initiation for Invertebrate and Vertebrate Neurons].

Recent studies have revealed.that in contrast to invertebrate systems, the initiation of action potentials in vertebrate neurons significantly differ from the relatively slow exponential dynamics predicted by Hodgkin-Huxley equations, but rather is characterized by a sharp onset with a kink. These data provided new insights into the link between action potential initiation and abilities of neurons and neuronal networks to encode. high frequency signals. Here, we review recent models describing sharp onset dynamics of action potential initiation, including an alternative model of cooperative activation of sodium channels, as well as the influence of the dynamics of action potential initiation on computational abili- ties of neuronal networks. The importance this topic is due to the fact that, despite the rapid development of neuronal modeling during last decades, the well established models are unable to capture experimentally observed details of the onset dynamics of action potentials in mammalian neurons and the abilities of neurons to reliably encode code high frequency signals Recent advances of experimental and theoretical analysis of generation of action potentials and neuronal encoding, presented in this review, are ofgreat importance for better understanding of neuronal processing and development of a more precise and realistic neuronal model.

Dynamics of responses of V1 neurons evoked by stimulation of different zones of receptive field.

The dynamics of receptive fields of 73 neurons in area 17 of cat visual cortex were studied using the temporal slice method. Three-dimensional maps of the receptive fields were plotted using the criterion of spike number in successive fragments (step 10 or 20 ms) of responses to 100 local flashes presented at different parts of the receptive field in random order. The size and configuration of such dynamically recorded receptive fields were then estimated. This allowed us to reveal the dynamic reorganization of all receptive fields 20-400 ms after stimulation. A small zone of responses appeared in the receptive field after initial latency, then it widened, received definitive configuration, and after that decreased and disappeared. The effect was reproducible under repeated estimations. The relationships between receptive field and the previously described orientation tuning dynamics, as well as between dynamics of receptive fields and their summation zones, mechanisms and possible functional meaning of the revealed effects for signal processing in the primary visual cortex are discussed.

[Interaction of the cerebellar cortical neurons in the cat: a cross-correlation analysis]. / Vzaimodeistvie neironov kory mozzhechka koshki: krosskoreliatsionnyi analiz.

Interactions between neurons in the cortex of cat cerebellum were investigated by the crosscorrelation analysis in acute experiments. Excitatory connections of various effectiveness were revealed in 13 of 90 pairs of simultaneously recorded neurons (14%). Very high percentage of inhibitory connections was found. They were observed in 38 pairs (42%). Neurons in 36 pairs (40%) had common inputs. Changes in duration and effectiveness of the interneuronal connections under different conditions of stimulation were found. Facts observed are discussed in connection with the already known data concerning functional organization of the cerebellar cortex. Possible causes of such a great number of revealed inhibitory interactions are discussed.

[Features of the dynamic reorganization of the receptive fields of visual neurons of the cerebral cortex and lateral geniculate body in the cat in response to changes in the parameters of photic stimulation]. / Kharakteristiki dinamicheskoi perestroiki retseptivnykh polei zritel'nykh neironov kory bol'shikh polusharii i naruzhnogo kolenchatogo tela koshki pri izmenenii parametrov svetovoi stimuliatsii.

Influence of parameters of local light stimulation of different points of receptive fields on characteristics of previously observed dynamic reorganization of recorded receptive fields of visual cortex and lateral geniculate neurons in time microintervals was studied in details in computer-controlled acute experiments on unanesthetized immobilized cats. The dependence of this process on the background illumination level, on intensity, contrast, area, duration, energy and orientation of a local rectangular or round light stimulus flashing in a random order at 100 points of the tested part of the visual field was determined. The analysis of the data obtained suggests a specificity of the influence of the background illumination level, intensity, area, duration and orientation of the stimulus on the dynamic reorganization of the receptive field. All the parameters were revealed to have a significant nonmonotonic influence on the receptive field parameters. The found effect is discussed for its probable functional significance and a possibility of its participation in process of information coding in the visual system.

[Differences in the dynamics of the visual receptive field and its summation zones in the cat]. / Razlichiia v dinamike zritel'nogo retseptivnogo polia i ego zony summatsii u koshki.

In acute computer-controlled experiments on immobilized unanasthetized cats, dynamic reorganization of the recorded receptive field and its summation zone were compared for lateral geniculate body and cortical neurons. Counterphasic development of these processes was observed and investigated in detail, i.e. enlargement and then narrowing of the recorded receptive field as compared with narrowing and then enlargement of the summation zone. Differences of physiological mechanisms of these two processes and their possible functional role are discussed.