Spatial summation processes in the receptive fields of visually driven neurons of the cat's cortical area 21a.

The spatial summation in receptive fields (RF) of single neurons in cat's extrastriate area 21a was investigated as a basic neurophysiological substrate for central integration processing of visual information. The results showed that the majority of investigated neurons changed their response patterns with gradual increase of applied stimulus size. In approximately 82% of cases the suppression of neuron discharges was observed when the length of the moving strip exceeded that of the RF. In some neurons the increased size of the moving stimulus leads to the changes in the RF substructure. Receptive fields of neurons recorded at the same microelectrode penetration depth showed a great variety of RF superpositions distributed in a spatially asymmetric manner. As a result, every single RF consists of multiple sub-regions within the RF, differing from each other by the number of superimposed RF-s (density factor). We suggest that such complex spatial organization of the RF provides the neurophysiological basis for central integration processing of the visual information.

Spatial organization of receptive fields of cat's. Hippocampal visually driven neurones.

According to the spatial configurations of receptive fields two broad groups of neurones in dorsal hippocampal region (HR) were distinguished. The receptive field borders of 22 cells have regular (R) smooth contours (squares or rectangles), usually with a horizontally oriented longitudinal axis. The second group was composed of neurones (20 cells) with irregular (IR) configurations of receptive fields. Some neurones (16 cells) of this group had relatively simple spatial configurations of receptive fields and 4 neurones had receptive fields with more intricate spatial configurations which formed complex geometrical shapes in the visual field. The exploration of the distribution of response properties a to stationary flashing spot over the RF surface revealed that the majority of cells with regular receptive fields have heterogeneous stationary structure with ON, ON-OFF and OFF subregions sequentially located in the receptive field, and these neurones, as a rule, were direction-sensitive. The neurones with irregular receptive fields, on the other hand, had a rather homogeneous structure of RFs when tested by a stationary flashing spot and only four neurones of 20 investigated were directionally sensitive.

Responses of cat's dorsal hippocampal neurones to moving visual stimuli.

Response properties of visually driven neurones in the cat's hippocampal region were investigated. Out of 688 single cells observed 181 (26%) were visually driven. Ocular dominance was determined for 147 of those cells, 90 of which were driven only by the contralateral eye, 20 were driven exclusively by ipsilateral eye and 37 neurones could be activated by both eyes. Receptive field boundaries were outlined for 157; 152 of those neurones were movement-sensitive, and 125 neurones were sensitive to stationary stimuli. A small group of neurones (13%) showed more pronounced reactions to the vertical direction of motion. Some neurones (22%) revealed sensitivity to the shape and size of the applied visual stimuli. These results confirmed earlier data indicating that visually driven neurones in hippocampal region possess complex properties. They are probably involved in a higher level of visual information processing.

Spatial summation processes in visually driven neurones of cat's pretectal region.

The spatial summation processes of single neurones of cat's pretectal region were investigated with moving and stationary visual stimuli. The results indicate that the majority of the investigated neurones changed their responses essentially at the gradual increase of size of the applied stimuli (i.e. showed negative or positive summation). Particularly, direction non-sensitive neurones showed symmetrical changes of spatial summation curves in response to two opposite directions of movement. By contrast, in some direction sensitive neurones different characteristics of responses for the two opposite directions of movement were observed. Thus the number of discharges in the responses to the preferred direction could increase or decrease at the gradual increase of the moving stimulus size, while the responses to the null direction could remain stable or vice versa. The same was observed for the "ON" and "OFF" responses in the ON-OFF neurones. Thus, it appears that the pattern of responses of a given neurone to different directions of movement and to the "on" and "off" periods of stationary stimulation are shaped by independent mechanisms.

[Structure of receptive fields of visually sensitive neurons of the cat hippocampus]. / Stroenie retseptivnykh polei zritel'nochuvstvitel'nykh neironov gippokampa koshki.

Structure of receptive fields of visually sensitive neurons in areas CA1 and CA3 of the dorsal hippocampus was investigated in alert cats with the brain-stem pretrigeminal section. The receptive field (RF) structure of 76 hippocampal neurons was analyzed by methods of scanning the RF by moving stimuli and mapping all their surface by a stationary flashing spot. According to presented data the neurons were classified into three groups: neurons with homogeneous structure of the RF (54%), with nonhomogeneous (28%) and neurons more sensitive to stimulus motion (18%) than to a stationary flashing light. Experiments have shown that responses of hippocampal neurons are highly specific ones. Thus, 9% of neurons with the nonhomogeneous RF structure have shown specific responses to variation of the contrast and contours of moving stimuli. The presented results show that hippocampal visually driven neurons have well developed mechanism for processing visual sensory information and apparently this quality ensures participation of the limbic system in visually controlled behavior of the animal.

Properties of the visually driven neurons of cat's hippocampal regions CA 1 and CA 3.

Neurons in areas CA 1 and 3 of cat's dorsal hippocampus were studied. Fifteen percent of the investigated cells were influenced by visual stimuli. Eighty five such neurons were investigated. The organization of their receptive fields was tested with stationary and moving visual stimuli. Twenty eight percent of neurons had small receptive fields (10-20 deg square). Forty one neurons responded to stationary flashing spots. They were ON-OFF, ON and OFF types with phasic (66%) and tonic (34%) characteristics. Seventy five responded to dark and bright stimuli moving across their receptive fields. Twenty five neurons were direction-sensitive and 21 responded better to the dark moving stimuli than to the bright ones. No significant differences in the response properties of neurons in the CA 1 and CA 3 fields were observed.

Properties of visually driven neurons in cats pretectal region.

Properties of visually driven neurons in the cat pretectal region were studied. A detailed investigation of the receptive field (RF) structure revealed, in the majority of neurons, irregular shapes of RF contours. Dark-sensitive and bright-sensitive zones of a neuronal RF had different spatial locations. The majority of pretectal neurons were movement-sensitive and reacted weakly to stationary flashing spots. Although no clear-cut orientation sensitivity was found in the pretectal neurons, some orientations of motion were, nevertheless, more effective. In some cases a non-directional response could be transformed into a directionally-sensitive one by changing the orientation of motion. Out data confirm earlier observations that the pretectal region is involved in the central processing of visual information.

[Responses of neurons of dorsal hippocampus field CA1 to visual stimulation in the cat]. / Otvety neironov polia CA1 dorsal'nogo gippokampa koshki na zritel'nye razdrazheniia.

In acute experiments on cats with pretrigeminal brain-stem section responses of 46 hippocampal neurons were investigated. Most neurons (71%) had small sizes of visual receptive fields. The responses of neurons to stationary stimuli were of phasic (66%), as well as tonic (34%) types. All neurons investigated responded to dark and bright spots moving across their receptive fields. 27% of sensitive neurons were direction-selective. Some neurons respond more intensively to moving dark spots in comparison with bright spots or bars. The results presented confirmed the suggestion that certain neurons in the CA1 field of the dorsal hippocampus have highly organized visual sensory input.