Осадчий Алексей Евгеньевич

Функциональное разделение частей «сенсомоторного комплекса» коры мозга человека методом магнитоэнцефалографии

2014 · ARTICLE · ru

В работе описывается попытка разработки способа неинвазивного картирования первичной моторной коры мозга человека. У 18 здоровых праворуких испытуемых исследовали магнитные ответы мозга, вызванные произвольными повторяющимися движениями указательного пальца правой руки. Разработанная методика показала принципиальную возможность локализации зоны М1 на групповом уровне у здоровых испытуемых

Resting state brain activity predicts individuals’ conformity

2013 · CHAPTER · en

The modification of judgments in a group situation: MEG correlates of conformity

2013 · CHAPTER · en

MEG study of social conformity

2013 · CHAPTER · en

Automatic processing of unattended lexical information in visual oddball presentation: neurophysiological evidence

2013 · ARTICLE · en

Previous electrophysiological studies of automatic language processing revealed early (100-200 ms) reflections of access to lexical characteristics of speech signal using the so-called mismatch negativity (MMN), a negative ERP deflection elicited by infrequent irregularities in unattended repetitive auditory stimulation. In those studies, lexical processing of spoken stimuli became manifest as an enhanced ERP in response to unattended real words, as opposed to phonologically matched but meaningless pseudoword stimuli. This lexical ERP enhancement was explained by automaticactivation of word memory traces realized as distributed strongly intra-connected neuronal circuits, whose robustness guarantees memory trace activation even in the absence of attention on spoken input. Such an account would predict the automatic activation of these memory traces upon anypresentation of linguistic information, irrespective of the presentation modality. As previous lexical MMN studies exclusively used auditory stimulation, we here adapted the lexical MMN paradigm to investigate early automatic lexical effects in the visual modality. In a visual oddball sequence, matched short word and pseudoword stimuli were presented tachistoscopically in perifoveal area outside the visual focus of attention, as the subjects' attention was concentrated on a concurrent non-linguistic visual dual task in the center of the screen. Using EEG, we found a visual analogue of the lexicalERP enhancement effect, with unattended written words producing larger brain response amplitudes than matched pseudowords, starting at ~100 ms. Furthermore, we also found significant visual MMN, reported here for the first time for unattended perifoveal lexical stimuli. The data suggest earlyautomatic lexical processing of visually presented language which commences rapidly and can take place outside the focus of attention.

Electrophysiological precursors of social conformity

2013 · ARTICLE · en

Humans often change their beliefs or behavior due to the behavior or opinions of others. This study explored, with the use of human event-related potentials (ERPs), whether social conformity is based on a general performance-monitoring mechanism. We tested the hypothesis that conflicts with a normative group opinion evoke a feedback-related negativity (FRN) often associated with performance monitoring and subsequent adjustment of behavior. The experimental results show that individual judgments of facial attractiveness were adjusted in line with a normative group opinion. A mismatch between individual and group opinions triggered a frontocentral negative deflection with the maximum at 200 ms, similar to FRN. Overall, a conflict with a normative group opinion triggered a cascade of neuronal responses: from an earlier FRN response reflecting a conflict with the normative opinion to a later ERP component (peaking at 380 ms) reflecting a conforming behavioral adjustment. These results add to the growing literature on neuronal mechanisms of social influence by disentangling the conflict-monitoring signal in response to the perceived violation of social norms and the neural signal of a conforming behavioral adjustment.

Магнитоэнцефалография – новейший метод функционального картирования мозга человека

2012 · ARTICLE · ru

Статья посвящена методу магнитоэнцефалографии (МЭГ) и его применению в когнитивных исследованиях. МЭГ – одна из современных технологий нейроимиджинга. Данный метод обладает уникальными характеристиками, позволяющими с высокой точностью локализовать источники активности нейронных популяций коры головного мозга человека в пространстве и времени. Наряду с исследованиями базовых сенсорных и моторных функций мозга, МЭГ является незаменимым инструментом исследования динамики когнитивных процессов памяти, внимания, эмоций и др. Особый акцент в обзоре сделан на использовании МЭГ для изучения мозговых механизмов языка и речи.

Connectivity measures applied to human brain electrophysiological data

2012 · ARTICLE · en

Connectivity measures are (typically bivariate) statistical measures that may be used to estimate interactions between brain regions from electrophysiological data. We review both formal and informal descriptions of a range of such measures, suitable for the analysis of human brain electrophysiological data, principally electro- and magnetoencephalography. Methods are described in the space–time,space–frequency, and space–time–frequency domains. Signal processing and information theoretic measures are considered, and linear and nonlinear methods are distinguished. A novel set of crosstime–frequency measures is introduced, including a cross-time–frequency phase synchronization measure.