CHARACTERISTICS OF Μ-RHYTHM FREQUENCY MODULATION UNDER IMAGINARY MOVEMENTS

The aim of the paper is to assess the phenomena of EEG frequency modulation while performing real and imaginary movements necessary for BCI control. Materials and Methods. The study enrolled a group of 30 volunteers of both sexes, aged 17 to 23. The subjects had to execute four commands and to run them randomly following the program instruction. The experiment was carried out in two ways: physically and mentally. Firstly, each command corresponded to a certain subject’s movement. Secondly, the same commands were not performed, they were only imaginary. The command was considered successfully executed if a volunteer was able to follow the program instruction and to hold the position for 2 seconds. The analysis of the results was carried out for five frequency ranges: 7–10 Hz, 9–12 Hz, 12–15 Hz, 15–20 Hz, 20–25 Hz. Results. Correlation analysis and exploratory statistics (namely, correspondence analysis and cluster analysis) were used to process the generated electroencephalographic parameters. The actually performed subjects’ movements were associated with a high number of low-frequency modulations in the 12–20 Hz range in the absence of modulating influences in the range below 12 Hz. Pronounced patterns of high-frequency modulation were peculiar for unexecuted commands. Conclusion. The results of the correlation analysis demonstrate a positive relationship between the number of cases of high-frequency modulation in the range of 9–12 Hz with the number of cases of low-frequency modulation in all other studied signal ranges in case of successful command execution. Key words: brain-computer interface, μ-rhythm, frequency modulation, EEG. Цель – оценка феноменов частотной модуляции ЭЭГ в условиях выполнения реальных и воображаемых движений, необходимых для управления ИМК. Материалы и методы. Для получения данных была сформирована группа из 30 добровольцев обоих полов в возрасте от 17 до 23 лет. Участники эксперимента должны были выполнить четыре команды и повторить их в неизвестном для них порядке, заданном программой. Эксперимент проводился двумя способами: физически и мысленно. То есть при первом способе каждая команда соответствовала определенному движению человека, при втором те же команды выполнялись воображаемо, движение представлялось мысленно. Команда считалась успешно исполненной, если добровольцу удавалось повторить и удержать заданное программой положение в течение 2 с. Анализ результатов проводился для пяти частотных диапазонов: 7–10 Гц, 9–12 Гц, 12–15 Гц, 15–20 Гц, 20–25 Гц. Результаты. Сгенерированные электроэнцефалографические показатели обрабатывались методом корреляционного анализа и методами разведочной статистики, такими как анализ соответствий и кластерный анализ. Реально выполняемые движения испытуемых связаны с высоким количеством низкочастотных модуляций в диапазоне 12–20 Гц при отсутствии модулирующих влияний в диапазоне ниже 12 Гц. Для случаев невыполнения команд характерны выраженные паттерны высокочастотной модуляции. Выводы. Результаты корреляционного анализа демонстрируют положительную связь между числом случаев высокочастотной модуляции в диапазоне 9–12 Гц с числом случаев низкочастотной модуляции во всех других исследуемых диапазонах сигнала в случае успешного выполнения команд. Ключевые слова: интерфейс «мозг – компьютер», μ-ритм, частотная модуляция, ЭЭГ.

EEG sensorimotor rhythms in children with autism spectrum disorders

One of the currently assumed causes of impaired social interaction exhibited by children with autism spectrum disorders (ASD) is dysfunction of the mirror neuron system (MNS), which is responsible for imitation, understanding the intentions and emotions of other people. Desynchronization of sensorimotor rhythms is considered to be the indicator of MNS activation. This study aimed to analyze the specific patterns of reactivity of the μ-rhythm in an individually determined frequency range and β-rhythm on the EEG in children with ASD during independent movements, observation, imitation and auditory perception of similar movements performed by another person. The data collected were compared to those describing normally developing children. The study involved right-handed children with ASD aged 5–10 (n = 10) and normally developing children (n = 10). In the independent movements exercise, β-rhythm desynchronization was more pronounced in children with ASD, with difference becoming significant in the P4 locus (p = 0.03). In the movements imitation exercise, the groups showed significant differences in the EEG μ-rhythm in the locus C3 (p = 0.03). Auditory perception of movements revealed significant differences in the ranges of both μ-rhythm (loci F3 and Fz (p = 0.02), F4 (p = 0.04), Cz (p = 0.009)) and β-rhythm (loci Fz (p = 0.01), F4 (p = 0.02)). In these situations, children with ASD exhibited synchronization of sensorimotor rhythms, while normally developing children showed desynchronization. The assumption is that the specific patterns revealed are the consequences of disruption of functions of MNS and anti-mirror system. The data obtained can be used in development of EEG biofeedback training protocols for children with ASD.

EEG μ-rhythm reactivity in children during imitation of biological and non-biological motion

The development of brain-computer interfaces based on the use of EEG sensorimotor rhythms reactivity parameters and designed for the rehabilitation of people (including children) with impaired motor functions is currently relevant. The study was aimed to analyse the EEG μ-rhythm in the individual frequency range in children during imitation of biological and non-biological motion. EEG was recorded at frontal, central and parietal cortical regions in 136 normally developing right-handed children aged 4–15, at rest and during the execution and imitation of movements using the computer mouse. When the children moved the computer mouse on their own (F1, 132 = 31.17; p < 0.001) and executed the concentric moving of the coloured circle (F1, 132 = 90.34; p < 0.001), the μ-rhythm desynchronization developed in the frontal, central and parietal neocortical regions. The μ-rhythm synchronization was detected during the non-biologocal motion imitation (F1, 132 = 12.65; p < 0.001), compared to the task on the autonomous movement execution. The μ-rhythm desynchronization was observed during the biologocal motion imitation in relation to autonomous movement execution (F1, 132 = 9.58; p = 0.002). The described effects had their own features in the groups of children aged 4–6, 7–9, 10–12 and 13–15. The study results demonstrate the desirability of taking into account the μ-rhythm reactivity age-related features and the visual stimuli nature when developing software for the brain-computer interfaces.