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L N Stankevich

Publications and source records attributed to L N Stankevich.

14 recordsLinked to original sources
PubMed2005

Characteristics of evoked potentials of the human brain during recognition of short acoustic stimuli of different frequencies.

We report here studies of the efficiency of recognition of short acoustic signals (11-30 msec) whose presentation did not produce mismatch negativity in evoked potentials in the human brain. Nonetheless, stimuli could still be recognized efficiently in these conditions; processing negativity disappeared from evoked potentials and the efficiency of recognition was significantly worsened on presentation of the shortest stimuli (11 msec). It is suggested that processing negativity also has a critical duration for acoustic signals, though this is significantly shorter than the minimum duration of stimuli needed for generating mismatch negativity.

Acoustic Stimulation↗
PubMed2005

Evoked brain potentials in adolescents in normal conditions and in attention deficit during solution of tasks requiring recognition of short-duration acoustic stimuli.

This study compares the effectiveness of the frequency-based recognition of short acoustic stimuli in groups of adolescents with attention deficit and normal measures of attention in conditions of the standard "oddball" paradigm. Stimuli of duration 50 msec yielded insignificant intergroup differences, though adolescents with attention deficit discriminated signal of duration 11 msec significantly worse. These showed significant differences in evoked brain potentials even with standard stimuli, with a significantly greater amplitude for N2b waves and a decreased P3b component. Evoked potentials obtained in response to the deviant stimulus were characterized by a P3b wave of reduced amplitude in the group with attention deficit. These data provide evidence that adolescents with attention deficit show defined abnormalities in the processing of acoustic sensory information at the cortical level.

Acoustic Stimulation↗
PubMed2003

Mismatch negativity in evoked brain potentials in adolescents in normal conditions and attention deficit in response to presentation of short-duration acoustic stimuli.

Experiments were performed to measure the critical duration of acoustic stimuli at which the generation of mismatch negativity is still possible in auditory evoked potentials in the human brain, arising in conditions of presentation of standard and deviant stimuli differing in terms of frequency (1000 and 1200 Hz respectively). Studies were performed in two groups of adolescents (aged 11-14 years): 1) those with normal attention characteristics and 2) children with attention deficit. The results showed that normal children had the same critical duration for sound stimuli at which mismatch negativity could be generated as adults. Mismatch negativity still appeared at a stimulus duration of 50 msec, while the mechanism generating mismatch negativity did not operate at durations of 30 and 11 msec. In children with attention deficit, statistically significant mismatch negativity was not seen at all durations of short acoustic stimuli (11, 30, and 50 msec).

Acoustic Stimulation↗
PubMed2003

Mechanisms of generation of mismatch negativity and their role in the recognition of brief auditory stimuli.

The endogenous components of auditory evoked potentials were studied in the human brain, arising in conditions of voluntary and involuntary attention. Variation of the duration of acoustic stimuli led to a situation in which the generation of mismatch negativity was blocked. The recognition of acoustic stimuli was compared in conditions in which passive perception of the deviant signal in some cases evoked mismatch negativity and in others did not. This demonstrated the following: 1) stimuli not evoking mismatch negativity in the classical "oddball" paradigm can be recognized efficiently; 2) recognition of stimuli evoking mismatch negativity (in conditions of passive perception) occurs with a significantly shorter response time. The difference in the present experiments was 49-51 msec. There was also an increase in the proportion of correct responses to the deviant stimulus (to 92%). Thus, if the experimental conditions allow the mechanism generating mismatch negativity to trigger, then the response time to the actively perceived stimulus decreases. These results are evidence that the mechanisms of involuntary attention contribute to the active perception of acoustic stimuli.

Acoustic Stimulation↗
PubMed2003

[Evoked potentials in the brain of adolescents in norm and those with attention deficit during recognition of short-term acoustic stimuli].

The effect of stimulus duration on auditory event-related potentials and performance of oddball task was studied in normal children and those with attention-deficit symptoms. Mismatch negativity was absent on presentation of short-term (11 ms) stimuli and present with longer stimuli (50 ms). The adolescents with deficit of attention performed much worse (errors of omission) with the short stimuli. The RT was significantly larger in subjects with attention-deficit with all types of tested stimulus duration. They also manifested a smaller P3b amplitude in response to task-relevant deviant stimuli and larger N2b peaks in response to the standard stimuli. It was possible to differentiate between the MMN and the N2b components owing to the fact that the MMN was absent with shorter stimuli. The findings suggest that there is a deficit in processing of sensory information at the cortical level in subjects with the attention-deficit symptoms.

Acoustic Stimulation↗
PubMed2003

[Human brain evoked potentials and discrimination of short acoustic stimuli with various frequency].

We found that the mismatch negativity (MMM) was absent in evoked potentials in passive condition for frequency deviant acoustical stimuli when stimulus duration was only 11-30 ms. But it was shown that it is possible for participants to fairly well discriminate these stimuli and the component N2b in RP was generated without preceding MMN. Processing negativity also was absent in potentials by the minimal stimulus duration (11 ms). Auditory discrimination nevertheless was still possible, but reaction time and number of committed errors increased significantly.

Acoustic Stimulation↗
PubMed2002

[Mismatch negativity in the brain evoked potentials induced by short duration acoustic stimuli in adolescents in the norm and those with attention deficit].

The effect of stimulus duration on the mismatch negativity of the auditory event-related potentials was studied in healthy children and those with attention-deficit symptoms. The minimum stimulus duration with which a MMN was elicited by frequency deviant was 50 ms in healthy children. The MMN was absent with shorter stimuli (11 ms and 30 ms). These parametres are close to those in adults. As to children with attention-deficit symptoms the MMN was insignificant with all tested stimulus durations (11 ms, 30 ms, 50 ms).

Acoustic Stimulation↗
PubMed2002

[Mechanisms of generation of mismatch negativity and their role in discrimination of short acoustical stimuli].

The effect of stimulus duration on the mismatch negativity in the auditory event-related potentials was used to study the role of mismatch negativity (MMN) in discrimination of short acoustical stimuli. We compared discrimination of different short acoustical stimuli in active variant of "odd ball" paradigm. It was shown that it is possible to discriminate between standard and deviant acoustical stimuli which do not produce MMN in passive condition. It makes possible to estimate behavioural significance of MMN in active discrimination task. If the MMN had not been recorded in passive condition, that leads to an increase of reaction time in active paradigm approximately by 50 ms.

Acoustic Stimulation↗
PubMed1988

[Changes in the ultrastructure and morphometric parameters of the cortical axospinal synapses as affected by a calcium-free medium].

Slice preparations of the white mouse sensorimotor cortex were examined for the morphometry of axospinal synapses in the material obtained under a standard experimental procedure and in sections perfused in calcium-free medium. The calcium-free medium in slice preparations was shown to reduce considerably the spine length and to increase the amount of spines with a negative curvature of the spine head in the contact area. Besides, it is noticed that the postsynaptic thickening grows, the active zone length decreases, the number of perforated contacts drops and the spine apparatus moves to the dendritic zone. It is supposed that the spine apparatus transfer is probably due to the reorganization of spine cytoskeleton, i.e., it is determined by both the motor activity of dendritic microtubules and the polymerization level of spine microfilaments.

Animals↗
PubMed1976

[Evoked potentials in the optic tectum of the carp brain upon electric stimulation of the facial nerve].

The evoked potentials in the carp tectum opticum in response to stimulation of the afferent pathway for chemical nonolfactory reception, the facial nerve, are positive deflections of 5-25 ms latency which do not reverse during microelectrode submersion. According to the evoked potential amplitude and latent period 7 active zones were distingnished in the ipsilateral tectum differing from each other either in one or in both parameters. The dependence of the response evoked by facial nerve stimulation in the tectum opticum on the impulsation from the medulla is proved by the difference in latency and by disappearance of the response in the tectum while persisting in the medulla after disconnection of both areas of the brain. The existence of efferent influences from the tectum upon the primary centre is suggested as the tectum ablation causes in some parts of the medulla either complete disappearance of the facial evoked potentials or changes in their parameters.

Animals↗