Biomedical subjects

J D Kropotov

Publications and source records attributed to J D Kropotov.

6 recordsLinked to original sources

PubMed1991

Subcortical neuronal correlates of component P300 in man.

Multiunit activity together with event-related potentials (ERP) were recorded from subcortical sites (the globus pallidus, the ventro-lateral nucleus of the thalamus and adjacent areas) in parkinsonian patients bearing electrodes for diagnosis and therapy. The patients viewed brief flashes of a visual stimulus (digit 6 or 9) randomly interspersed at 5-10 sec intervals. The patient's task was either to count silently the number of digit 6 or to press a button in response to its presentation. In the first part of the test (128 trials) the probability of the relevant stimulus was 0.25 while in the second part (another 128 trials) it changed to 0.75. Peristimulus time histograms for impulse activity of each neuronal population, averaged ERPs as well as profiles of neuronal reactions for the whole set of electrodes were computed and statistically analyzed. This study revealed the existence of subcortical P300-like activity that depended upon stimulus probability in the same way as the cortical P300 recorded from scalp electrodes. Components of responses of neuronal populations correlated with the components of subcortical ERPs were separated. The data support the multiple origin of the P300. The subcortical P300-like activity is suggested to be an electrophysiological reflection of the program selection mechanism implementing the selection of the patient's response from the set of possible programs.

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PubMed1991

Human depth ERP in a visual threshold recognition task.

Event-related potentials (ERPs) were recorded from the globus pallidus, the N. ventro-lateralis thalami and adjacent areas in parkinsonian patients bearing gold electrodes for diagnosis and therapy. The patients participated in a recognition task in which visual stimuli (digits) were presented at threshold durations. The ERPs from each single recording site, as separate histograms and then in combination as composite histograms across all recording sites ('profiles of reactions' and 'profiles of reaction differences'), were computed for 3 response types (correct, non-recognition, and incorrect). Four groups of depth-ERP components (N100, P200, N300, P300) were observed. The N100 was not found to be affected by the quality of recognition, manifest in type of response, while the later components were, but each in its own way. A comparison of these data with those of multiunit activity recorded from these same sites (see Bechtereva et al. 1990) shows that the pattern of the depth N100 and P200 components with reference to the 3 types of response have no observable counterparts in the impulse activity manifestations of subcortical neuronal populations, while the depth N300 and P300 are indeed associated with the neuronal impulse activity. This in turn supports the hypothesis concerning multiple (including subcortical) generators of the P300.

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PubMed1990

In search of cerebral error detectors.

Multiunit activity was recorded from 124 different subcortical sites in 10 parkinsonian patients bearing gold electrodes for diagnosis and therapy. The patients participated in a visual recognition task in which the stimuli (digits) were presented on a LED-matrix at threshold, the exposure times so chosen that in about half the trials the patient failed to recognize the digit correctly. Peristimulus time histograms (PSTHs) for each neuronal population as well as profiles of reactions for all neuronal populations were calculated and statistically analysed, separately for the cases of correct, incorrect, and non-recognition. There are at least 3 groups of neuronal populations, each associated with one temporally separate neurophysiological process involved in the performance of the psychological recognition task. They can be differentiated by the parameters' 'onset' and 'peak' latency. This in itself suggests that they may be related to different psychological processes involved in the task's performance, the earlier components in feature detection and/or evaluation operations concerning the stimulus; the later components, presumably, in processes related to initiation of the actual response. By scanning the individual PSTHs, we found one neuronal population which might be considered an error detector. This population reacted robustly in the early stages of information processing (100-500 ms post-stimulus) only in the case of non-optimal behavior, suggesting that it might somehow be related to signalling an error.

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PubMed1989

Human thalamic and pallidal neuronal responses to visual stimuli in a threshold recognition task.

Multiunit activity was recorded from 80 different subcortical sites in 9 parkinsonian patients bearing gold electrodes for diagnosis and therapy. The patients participated in a visual recognition task in which the stimuli (digits) were presented on a LED matrix at threshold. The exposure times were so chosen that in about half the trials the patient failed to recognize the digit correctly. Peristimulus time histograms for each neuronal population as well as profiles of reactions for the groups of neuronal populations localized in the N. ventro-lateralis thalami and the globus pallidus, respectively, were analysed statistically, contrasting the cases of correct recognition with those of non-recognition. Different types of response, possibly related to different stages of task performance, were separated: an early type with onset latencies ranging from 80 to 160 msec, two middle types with onset latencies ranging from 200 to 300 msec, and a type characterized by slow shifts in the discharge rate beginning 400-600 msec post stimulus. Most of the significant differences in the discharge rate between qualities of recognition were found in the middle-type responses and in the slow shifts, shorter latencies and larger amplitudes accompanying correct recognition.

Adult↗

PubMedDate not supplied

Event-related neuronal responses in the human strio-pallido-thalamic system. I. Sensory and motor functions.

Multiunit activity was recorded from strio-pallido-thalamic sites in parkinsonian patients bearing gold electrodes for diagnosis and therapy. The patients voluntarily participated in tasks designed to study neuronal correlates of both physical and semantic characteristics of stimuli as well as motor responses. Six modifications of the stimulus-response paradigm were used: visual odd-ball, visual and acoustic odd-ball tasks; tasks in which either the stimulus intensity or the meaning of non-target stimuli varied; single-stage delayed response and dual-stage delayed response tasks, respectively. In each task the patients had to evaluate some of the stimulus characteristics and to respond in a particular way according to the preliminary instructions. Peristimulus time histograms for each multiunit separately as well as profiles of reactions and profiles of reaction differences for the whole set of multiunits were calculated and subjected to statistical analysis. Two functional groups of subcortical neuronal reactions, stimulus-related and response-related activities, were separated. The stimulus-related activities of most multiunits were modality-unspecific. Their most striking feature was dependence on stimulus relevance and also its probability, the strongest reactions observed in response to task relevant stimuli occurring with low probability. The response-related activities occurred prior to initiation of movements, dependent upon the particular action and its probability. The data suggest at least two different and spatially overlapping subcortical channels responsible for goal-directed behaviour: the one related to stimulus assessment and the other to preparation for motor action.

Adult↗

PubMedDate not supplied

Event-related neuronal responses in the human strio-pallido-thalamic system. II. Cognitive functions.

Multiunit activity was recorded from the strio-pallido-thalamic system in the same parkinsonian patients (as described in the previous paper) who bore gold electrodes for diagnosis and therapy. The patients voluntarily participated in various tasks designed to study neuronal correlates of cognitive functions: "odd-omissions," "short-term memory," "cued bimodal," "assessment," and "dual-stage delayed response" tasks. Preparatory-related activities were found in multiunits reacting to sensory cues. In a few multiunits these activities depended upon the specific features of the stimuli that were anticipated for evaluation. The most striking characteristic of stimulus-related activity was the suppression of the multiunit responses when the stimuli become behaviourally meaningless. The hypothesis of action programming is discussed: the loop, including the cortex, neostriatum, pallidum and appropriate parts of the thalamus, is involved in the selection of actions, thus providing the organization of sequential behaviour.

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