Biomedical subjects

S Sobótka

Publications and source records attributed to S Sobótka.

17 recordsLinked to original sources

PubMed2000

Involvement of single unit activity in inferotemporal and perirhinal cortices in recognition memory of visual objects in the macaque.

Recognizing objects from the past is a vitally important ability for everyday live. The studies of brain mechanisms responsible for visual recognition memory suggest that the modulation of single unit activity in the inferotemporal and perirhinal cortices could be an important part of the neuronal substrate of recognition memory. In this review, I will describe Stimulus Specific Adaptation (SSA)--the reduction in neuronal response to previously viewed objects. The experimental tasks in which SSA is observed will be presented, along with the possibility that SSA may be enhanced by saccadic exploration of visual scene. Next, I will demonstrate that under special circumstances (partially split-brain preparation) monkeys could recognize the re-presentation of visual images without the concomitant appearance of SSA. The most promising alternative candidate for neuronal mechanism involved in recognition memory is delay activity--an increased frequency of cell firing in the time between the initial presentation of an image and its subsequent re-presentation. In order to determine if delay activity is important for recognition we have started to investigate the effects on recognition memory of disrupting delay activity by electrical stimulation. Preliminary results indicate a positive correlation between a reduction in delay activity and a decrease in recognition performance.

Animals↗

PubMed1992

Hemispheric asymmetry in event related potentials associated with positive and negative emotions.

Event-related potentials from symmetrical points of the left and right frontal and occipital cortex were recorded while subjects experienced positive and negative emotions. The emotions were elicited by either missing or hitting a target with a photoelectric gun. Twenty three right-handers (10 males and 13 females) were tested. Each subject took part in two sessions. In the first session the subjects were informed about their performance (hit or miss) after each shot. In the second, control session, no feedback was given. The amplitudes of P180 potential registered from the occipital cortex were higher in the right than in the left cerebral hemisphere, irrespectively of subjects' performance (i.e. a miss or a hit). No such tendency was observed in potentials registered from the frontal cortex. These regularities emerged only in the feedback situation, i.e. when subjects were informed about their performance, although higher ERPs were registered for hits than for misses. The results support the hypothesis that the posterior region of the right hemisphere is more engaged than the left one in experiencing emotions, irrespectively of their sign.

Adolescent↗

PubMed1989

Hemispheric differences in evoked potentials to faces and words.

Sixteen right-handed subjects (8 male and 8 female) were asked to compare two faces or two words successively presented at the centre of the visual field. The brain's electrical activity was recorded from the scalp at symmetrical points of the left and right occipital lobes (0(1) and 0(2)) and posterior temporal lobes (T5 and T6). The reference electrode was placed on the scalp vertex (Cz). A multi-factor analysis of variance revealed significant hemispheric differences of the N243 and P406 amplitudes. For the N243 the opposite asymmetry was found for faces and words. For the face matching the N243 amplitude was higher in the right hemisphere, whereas for word matching it was higher in the left hemisphere. For the P406 the asymmetry was in the same direction both for faces and words, with higher amplitude in the left hemisphere. In the case of face matching the hemispheric difference in the P406 was more pronounced, due to a negative shift of the potential in the left hemisphere in the latency range of 200-1,500 ms. Functional asymmetry of the brain in face perception thus appears to be reflected in the brain's electrical activity. We conclude that differentiation in hemispheric functions takes place while encoding information about stimulus in short term memory.

Adult↗

PubMed1985

Right hemisphere superiority in the perception of different kinds of non-verbal material.

Hemispheric asymmetries in different perceptual functions have been tested using the method of lateral presentation of stimuli i.e. in the left or right visual field. The first two experiments showed the right hemisphere advantage in the accuracy of detection of stereoscopic depth and in the strength of the tilt after-effect, i.e. in such phenomena which seem to be produced in the striate cortex. The third experiment, in which evoked potentials from point 01 and 02 during face perception were recorded, revealed the existence of right hemisphere superiority as early as 150 ms after stimulus presentation. These results indicate that the two hemispheres can already differ in their functions at the sensory level of processing.

Depth Perception↗

PubMed1985

Event-related potentials associated with positive and negative emotions.

To study the cortical regulation of emotions, event-related potentials (ERP) were recorded in the situation of a television tennis game. Winning the ball was used as a model of a positive and losing it was that of a negative emotional reaction.

Adult↗

PubMed1984

Hemispheric differences in evoked potentials to pictures of faces in the left and right visual fields.

Fifteen right-handed women evaluated the similarity of two faces presented to them either in the left or in the right visual field. The subjects' task was to decide whether the faces were the same or different and accordingly to press a button or abstain from doing so. Errors made by the subjects and the visual evoked potentials (VEPs) from points O1 and O2 referred to point CZ were recorded. Behavioural and electrophysiological results demonstrated the superiority of the right hemisphere in the perception of faces. The subjects made fewer errors when faces were presented in the left visual field. The number of errors also decreased when the presented faces were different from each other. Analysis of the VEPs indicates the existence of hemispheric asymmetry as early as 100 msec after the first stimulus disappeared. The asymmetry is larger in response to the second stimulus. On the basis of these results we conclude that differentiation in hemispheric functions takes place in the phase of short-term memory. The smaller number of errors made when the presented faces were different we explain by the strategy applied by the subjects.

Adult↗

PubMed1982

Visually evoked potentials to pattern stimuli in cortex of binocularly deprived cats.

Visually evoked potentials (VEPs) were compared in 7 normally reared cats (N cats) and 9 cats deprived of pattern vision during postnatal period. In 4 deprived cats (D cats) recording was done immediately after deprivation period which lasted from 6 to 24 months. In 5 cats (DE cats) 6 months of deprivation was followed by 4-18 months of visual experience. Two stimuli were used: a large stationary stimulus (a 30 per 30 degrees grating pattern illuminated by flash) and a small moving stimulus (a smaller grating pattern was located in different parts of visual field and illuminated by a moving 1 per 4 degrees light slit). The VEPs were recorded in the marginal, suprasylvian, ectosylvian and sigmoid gyri. As compared with N cats, in D cats the VEPs in all cortical areas were of simpler form, more variable and of greater amplitude. Moreover, in contrast to N cats, in D cats the VEPs were of similar amplitude when evoked from the contra or homolateral visual field. However, results in DE cats showed that these changes are largely reversible.

Animals↗

PubMed1970