Search

The P300 component of the evoked potential was recorded over both hemispheres in order to study interhemispheric differences in the process of perception of subliminal verbal stimuli. The stimuli--subliminal words, neutral and emotional--were presented at random to the left or right visual fields. In response to an unrecognized emotional word, the amplitude of P300 wave increased diffusely over both hemispheres as compared to that to a neutral word, with no changes in interhemispheric differences. The interhemispheric difference changed considerably in the presence of an 'unaccountable' emotion caused by a subliminal word. This suggests a unilateral activation of the right hemisphere and a predominant role of this hemisphere in the cortical organization of the unconscious function 'unaccountable' emotion.

The analysis of the late positive wave (component P300) of an averaged evoked potential, recorded to visual stimuli in different experimental situations has shown that local activation of the cerebral cortex during conscious experience (Pavlovian "light spot") is of a dynamic nature and is determined by signal significance of stimuli and predominant voluntary activity. In cases when it is necessary to decide on the choice of reaction anterior areas of neocortex are activated. If the function of perception is dominating the local activation essentially occurs in corresponding cortical area at which the perceived stimulus is timed. The cortico-thalamo-cortical mechanism of focused attention and its role in providing for conscious human experience is discussed.

Reaction time was recorded in adult healthy people at pauses of 80, 110, 150, 200, 300, 500 and 800 ms between the warning and the triggering stimuli. The warning signal determined the choice of reaction. The stimuli were presented to different halves of the visual field at random. 200 ms pause between the warning and the triggering stimuli is critical for the reaction time. Beginning with this interval, the reaction time was considerably reduced. When information from the triggering stimulus reached "directly" the hemisphere which was "to produce" the motor response, reaction time was considerably shorter, than at non-coincidence of these two factors. The influence of their combination on reaction time is particularly pronounced at 150-500 ms pauses between the warning and the triggering stimuli. The data obtained suggest that the decision making results in a lateralized activation of the hemisphere, which is "to produce" the motor reaction. As a rule, reaction time is not influenced by spatial location of the warning signal. The results of the work should be taken into account when organizing activity of an operator.

The study was made on healthy adult subjects. The reaction time of the hand (RT) was measured under two conditions: 1) the choice of reaction (right or left hand) is determined by the nature of the warning stimulus; 2) decision on the choice is taken, depending on the second, trigger stimulus. Stimuli are presented at random sequences to different visual fields. The reaction time to the visual signal presented to the visual field ipsilateral to the hand is significantly shorter (by 15 to 26 msec) than to the stimulus in the contralateral visual field. In a simple motor reaction, when no discrimination of trigger stimulus and the decision on the choice of reaction is required, a hemispheric asymmetry of reaction time is manifested: the left hemisphere only responds differently to direct visual stimulation and to that mediated through the contralateral hemisphere.

Recognition of short time intervals (10, 60, and 180 ms) between visual stimuli presented to the left or right hemisphere was studied in adult healthy people. The interval of 180 ms is recognized better than that of 10 or 60 ms. Learning with repeated tests with 180 ms intervals proceeds better than that with short intervals. The predominance of the left hemisphere has been revealed only for perception of 10 ms interval. The other time intervals asymmetry is not observed. It is suggested that the left hemisphere is predominant in estimation of short (less than 60 ms) time intervals. In formation of time nervous model a significant role is played by local activation of the cortical zone where the standard stimulus is addressed.

By means of backward masking, the time of perception of letter stimuli presented to the left and right visual fields, was determined in practically healthy persons who were given different doses of alcohol, and in patients with chronic alcoholism. Evoked electrical activity to the same stimuli was recorded in identical conditions. A small dose of alcohol (0.41 g/kg) increases in healthy subjects the time of perception of visual signals only if they are presented in the left visual field: a medium dose (0.82 g/kg) increases the time of stimuli perception in both halves of the visual field, but obviously more so in the left one, in patients with chronic alcoholism the time of perception is substantially longer in the left visual field. A small dose of alcohol does not affect evoked electrical cortical activity in healthy persons. Distinct regional differences are exhibited in the action of the medium dose of alcohol on the cerebral cortex of healthy persons. Evoked potential in the central area is depressed to a greater extent than in the visual and associative (Brodman field 37) zones. With chronic alcohol intoxication, evoked activity in the right hemisphere is depressed considerably more than in the left one.

Intramuscular injections of seduxen (10 mg), a benzodiasepin drug, with expressed tranquilizing and alarm suppressing effects, were used with the aim of experimental testing of a hypothesis on the neural mechanism of conditioned changes of the P300 wave. Under the action of seduxen no temporary connections could be formed between a perceived nonverbal visual stimulus and a unrecognized emotional word. The seduxen did not suppress the conditioned cortical reaction acquired due to combination of nonverbal stimulus with unrecognized emotional word. The suggestion is made that the necessary condition of temporary connection elaboration by means of a unrecognized verbal stimulus is the implication of the limbic structures where negative emotional reactions are integrated.

The influence of seduxen (diazepam) on cortical potentials P300 evoked by neutral and emotional words was studied in adult subjects having life conflicts. The therapeutic dose of seduxen (10 mg) had no significant effect on the amplitude of the late positive cortical response P300 to neutral words. Seduxen depresses the emotional activation of the cerebral cortex; that is manifested in selective elimination of those changes in latency and amplitude of P300 wave which are observed in response to emotionally significant words. Under the action of seduxen, the interhemispheric difference in the latency of cortical response disappears due to latency increase in the right hemisphere.

Recording of averaged evoked potentials to two successive visual stimuli shows that associations, temporary connections, direct and feedback, can be elaborated in man between two unrecognized stimuli. The magnitude of cortical late response to the first stimulus in the complex diminishes as a result of action of the inhibitory feedback temporary connection. This inhibitory effect is more pronounced when the second stimulus is emotionally significant for the subject. The evoked potential to the second stimulus in the association between unrecognized visual stimuli is considerably facilitated. The role is discussed of direct and feedback temporary connections between unrecognized stimuli in some unconscious psychic phenomena in man.

Recordings of the P300 waves in left and right hemispheres in response to neutral and emotionally significant words corroborate the rightfulness of the principle stating that any psychic function, for instance emotion, is organized and controlled by means of a close and complementary collaboration of both hemispheres. A predominance of a hemisphere manifests itself in organizing a certain stage of the integral emotional function.