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K Dec

Publications and source records attributed to K Dec.

At least 19 recordsLinked to original sources
PubMed2001

The spatial substructure of visual receptive fields in the cat's superior colliculus.

Although the direction selective properties of the superficial layer cells of the cat's superior colliculus have been extensively studied, the mechanisms underlying this property remain controversial. With the aim to understand the mechanism(s) underlying directional selectivity of collicular neurons we examined the substructure of their visual receptive fields. 1. The strength of cell responses and the direction selectivity indices varied in relation to the location of the tested region within the receptive field and the amplitude of stimulus movement. 2. Decrease of the amplitude of motion resulted in a decrease of direction selectivity index both in the group of direction-selective cells and in the group of cells classified as direction nonselective but with a directional bias. 3. The decrease of direction selectivity for small amplitude movement resulted mainly from increase in the magnitude of response in the nonpreferred direction of movement. 4. These results suggest that the receptive fields of most collicular cells are composed of subregions with different response profiles and indicate that inhibitory mechanisms dictate direction selectivity of collicular cells.

Action Potentials↗
PubMed1998

Summation effects in receptive fields of the cat's pretectal neurons to stationary and moving visual stimuli.

1. Numerous investigations have shown that the cat's pretectal region (PR) is involved in performance of various visual habits, visually guided behaviour and learning processes. Thus, visually driven PR neurons must have abilities to integrate incoming sensory information. 2. Responses of 102 PR neurons to moving and stationary visual stimuli were investigated in cats. Special attention was paid to the comparative characteristics of summation processes in the same neuron elicited by stationary and moving visual stimuli. 3. The results indicate that only a small proportion (20%) of pretectal neurons revealed similar courses of summation for stationary and moving stimuli. The great majority of neurons (about 80%) showed differentiated courses of summation, depending on the type of visual stimuli used. 4. These data indicate that there are probably discrete mechanisms in the PR which contribute to integration of sensory information in the visually sensitive cells according to the different types of visual stimuli used.

Animals↗
PubMed1996

Electrical activity of the acutely isolated pons in cats.

The cat's pons was isolated by two brainstem transections, at the junction of medulla and pons and at the junction of pons and midbrain. In the deafferented pons the EEG activity was virtually absent, whereas the spatial density of active units and the rate of their spontaneous spike activity were at a high level. In the pons of control preparations with brainstem transected only at the ponto-midbrain junction the EEG activity was present, while the single-unit activity was such as in the isolated pons. The electrical activity of the isolated pons was similar to that previously described in the cat's isolated midbrain. The discrepancy between EEG and single-unit activity suggests that in the deafferented pons or midbrain many neurones are asynchronously autoactive. Also, these results show that a flat EEG record is not necessarily a sign of absence of the neural activity and neural death.

Animals↗
PubMed1996

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.

Animals↗
PubMed1993

Influence of the intertectal connection upon visual responses in the cat's superior colliculus.

Visual responses of single units in the superficial layers of the superior colliculus were examined in cats with pretrigeminal brainstem transections and lesions in the contralateral superior colliculus. The percentage of direction selective cells was decreased in lesioned as compared to non-lesioned cats. This effect may be a result of the elimination of suppression from the contralateral superior colliculus as well as disturbance of the projections from other structures of the contralateral hemisphere.

Animals↗
PubMed1989

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.

Animals↗
PubMed1984

Barbiturate influence upon organization of lateral geniculate receptive fields in cats.

Under different levels of Nembutal anesthesia the spatiotemporal characteristics of receptive fields of cells in the lateral geniculate nucleus were investigated. All units decreased their maintained activity and bursts of spikes occurred spontaneously after administration of the anesthetic. The excitatory domains of the receptive fields were also changed by shortening of the cell's sustained response and enhancement of the postinhibitory transient responses; the spatial extent of these domains being less affected. A qualitatively new excitatory tertiary” domain appeared in the receptive field surround with a latency of 170-300 ms. These effects together with enhancement of the spatiotemporal extent of inhibitory domains suggest that the suppressive action of barbiturate takes place beyond the retina.

Animals↗
PubMed1984

The velocity-response curves of the cat's superior colliculus neurons.

The velocity-response curves of the cat's superior colliculus neurons responding to moving stimuli mere studied quantitatively. They were fitted by logarithmic Gaussian curves described by three parameters: optimal stimulus velocity, amplitude and dispersion of the curve. Since reversal of the stimulus movement direction changed neither optimal stimulus velocity nor dispersion of the velocity tuning curve, then the fourth parameter, directional asymmetry, is postulated to describe fully, in conjunction with three parameters mentioned above, the dependence of the neuron response to velocity and direction on the stimulus motion. All parameters were roughly normally distributed and uncorrelated with each other in the sample of cells investigated. Some implications of our results for the classification of cells, and some arguments for population coding” against single cell trigger feature coding are discussed.

Animals↗
PubMed1983

The influence exerted by Nembutal on reactivity of the superior colliculus neurons.

Effects of a Nembutal upon responses of the superior colliculus neurons were analyzed in pretrigeminal cats. Most cells were studied during the spindly barbiturate pattern in the EEG. In this condition collicular neurons lose their spontaneous activity, become sluggish in their reactivity to stimuli moving at high velocity, and less sensitive to direction of movement. After a further increase in the anesthesia down to the isoelectric EEG pattern the responses of neurons were gradually depressed and finally neurons became non-driveable by visual stimulation. A possible mechanism responsible for the reduction of the cells excitability is discussed.

Animals↗
PubMed1981

The structure of visual receptive fields of cat's pulvinar neurons.

Receptive fields of 382 neurons in the pulvinar were investigated. The observed receptive fields were classified according to the neurons’ responses to stationary flashing light spots positioned in different parts of the receptive field. New receptive field types with multiple discharge centers were observed. Neurons with these receptive fields generally responded with multimodal discharges to moving visual stimuli. The background illumination resulted in a decrease of the number of on-off and off receptive fields whereas the number of the on receptive fields became higher. In a majority of cases the receptive fields with multiple discharge centers lost their responsivness during background illumination. The changes in the receptive field sizes measured, by light spot in dark and light adapted conditions were attributed mainly to scattered light. The sizes measured by black stimuli under the same conditions remained constant.

Animals↗
PubMed1981

Responses of cat's pulvinar neurons to moving visual stimuli.

Visually-driven pulvinar neurons were investigated by moving visual stimuli. Of a total of 256 observed neurons 25 percent were not sensitive to the movement of light spots, but revealed a vigorious activity during the movement of black objects. According to the response pattern elicited by the motion of objects through receptive fields, neurons were classified as follows: (a) directionally non-selective – 41 percent, (b) directionally selective – 28 percent, (c) multimodal – 29 percent, (d) suppressed-by-contrast type – 2 percent. Background illumination exerts different types of influences on the movement-evoked spike responses in the pulvinar neurons. Eighteen percent of the neurons were not affected by background illumination. Eight percent of the neurons were transformed from directionally non-selective into the directionally selective ones, some of which reversed their preferred directions during background illumination (5 percent). Activity of 15 percent of the neurons was facilitated and of 21 percent was suppressed during various levels of background illumination. Twenty three percent of the neurons lost their spike activity when the background illumination was switched on.

Animals↗
PubMed1980

The response patterns of collicular neurons to moving stimuli in cats after lesion of the visual cortex.

The speed and direction selectivity of responses of collicular neurons in pretrigeminal cats following lesions of the visual cortex were examined using moving light spots. Following cortical lesions the number of cells showing direction selectivity was reduced, but the number of cells showing speed selectivity was increased. It is suggested that some of the characteristics of collicular neurons are dependent on initial organization of the intracollicular synaptic connections rather than the corticocollicular ones.

Animals↗
PubMed1979

Single-unit activity in cat's isolated midbrain.

The midbrain was isolated by two brainstem transections, pretrigeminal and premesencephalic. In the isolated midbrain, particularly within the reticular formation, EEG activity was greatly depressed. On the other hand, single-unit spike activity remained at a high level. The spatial density of active reticular units and the rate of their spontaneous activity were at least not smaller than those in the midbrain of the cat with only a pretrigeminal transection. Thus the flat EEG record is not necessarily a sign of the absence of neural activity.

Animals↗
PubMed1978

Single unit responses to moving spots in the superior colliculus of the cat's isolated midbrain.

The midbrain was isolated from the pons and forebrain by two brainstem transections, pretrigeminal and "preoptic", inclined at 32 degree or 35 degree to the vertical plane. The preoptic transection passed along the rostral border of the optic tract, leaving it and the chiasm intact. Thus, direct visual input into the isolated tissue was maintained. Single unit responses to a moving spot were investigated in the superior colliculus. This stimulus evoked vigorous responses in most cells. Of the 70 tested units, 25 showed direction-selectivity, 48 speed-selectivity and 47 reacted to diffuse flash. Compared to cats with only pretrigeminal transection only the number of direction-selective units was reduced. The reduction was similar to that found previously in cats with ablated visual cortex or visually deprived from birth. Thus, the cells of the isolated superior colliculus show a striking degree of functional integrity.

Action Potentials↗
PubMed1976

Effects of binocular deprivation of pattern vision on single unit responses in the cat superior colliculus.

Single unit responses in the superior colliculus of cats deprived of pattern vision from birth and of normally reared cats were studied in unanesthetized pretrigeminal preparations. Collicular units of deprived cats showed a diminished direction-selectivity but a somewhat better speed-selectivity compared to normals; they also preferred lowspeed stimuli, and reacted less frequently to diffuse flash. The impairment of direction-selectivity of collicular neurons may be partly responsible for the impairment of the pursuit eye movements in visually deprived cats.

Animals↗
PubMed1975

The effect of background illumination on the responses of the neurons of the cat's superior colliculus to moving stimuli.

The influence of background illumination on unitary neuronal responses of cat's superior colliculus to moving stimuli were investigated. Diverse types of neurons responding to background illumination were observed: Neurons which did not change their activity during background illumination; neurons in which the response to moving stimuli during background light was facilitated; cells in which the spatiotemporal dispersion of the peak of evoked response was narrowed with light adaptation; cells in which activity was suppressed during background illumination; and neurons in which the specific response was changed to an unspecific one (and vice versa) during background illumination. The background illumination itself did not evoke any response in the cell, and the suggestion was put forward that subthreshold influences could modulate the evoked activity of the neuron.

Animals↗
PubMed1974

Analysis of visual information in midbrain centers.

The role of pretectum and colliculus superior in the analysis of visual information was studied. Single unit responses to visual stimuli were recorded. Several types of responses were observed, including "suppressed by contrast", "direction non-sensitive" and "direction sensitive" responses. An attempt was made to define the place and mechanism of direction-sensitivity of the cell. The conclusion is put forward that horizontal cells in the first layers of retina are not responsible for direction-sensitivity. Detailed analysis of receptive field structure revealed "homogeneous" and "heterogeneous" types of receptive fields as shown by response patterns of the neuron to a flashing light spot positioned in different parts of the receptive field. Study of latency distributions also revealed both complex "heterolatent" and more simple "homolatent" organizations of receptive fields The effect of the intensity of background illumination was investigated. Results show that changing of the background illumination can influence the response pattern of a cell, and sometimes can influence the direction-sensitivity.

Animals↗