Age dynamics and topography of an individual EEG mu rhythm reactivity in children aged 4-14 years

Within the framework of the mirror neuron system related studies, there is a line of research dedicated to examining the effects of the EEG mu rhythm reactivity under conditions of observation and imitation of actions performed by others. It is hypothesized that the analysis of the mu rhythm activity at central electrode sites can be taken as a relatively easy non-invasive method for examining the mirror neuron system activity in human. At that, it is important to take into account possible individual differences in the frequency of the mu rhythm which is thought to reflect the activation level of the primary sensorimotor cortex. It is necessary to differentiate it from other alpha-like EEG oscillations related to different functional systems of the neocortex. Besides, in children the frequency of the mu rhythm tends to gradually increase with age. Hence, it seems important in such studies in the first place to functionally define the individual mu rhythm frequency for each participant under relevant conditions of a selfpaced motor activity. The main aim of our research was to study the reactivity patterns of the individual mu rhythm under different conditions in children in the following age groups: “preschoolers” (4-6 years), “younger schoolchildren” (7-10 years), “adolescents” (11-14 years). In 87 typically developing children aged 4-14 years, we analyzed the EEG recorded at the following electrode sites: F3, Fz, F4, C3, Cz, C4, P3, Pz, and P4. The experimental conditions (30-second long each) were as follows: fixation of one's sight at a motionless computer mouse, self-controlled circular righthand movements (prior to and after the condition of movement observation), visual observation of similar movements performed by another person, real time imitation of observed movements, and hearing of familiar sounds produced by the computer mouse movements with eyes closed. We used repeated measures ANOVA to assess the main effects of the age group and experimental condition variables and their interaction on the amplitude of the individual mu rhythm. In this research, we discovered patterns of individual EEG mu rhythm reactivity under conditions of observation, imitation, and auditory perception of movements with the computer mouse. The mean values of the median frequency within the individual mu-ranges were as follows: 10.1 ± 1.2 Hz for “preschoolers”, 9.9 ± 1.4 Hz in the group of “younger schoolchildren” and 10.6 ± 1.1 Hz for “adolescents”. 121 children aged 4-14 years took part in the study. This research was conform to ethical principles of the declaration of Helsinki, 1964. Parents, after being provided with necessary information,gave their consent to their children's participation in the research. The condition of performing self-paced circular mouse movements showed distinct left hemisphere lateralization of the individual mu rhythm suppression in all age groups, mainly, in central and parietal leads (See Fig. 1). Higher indices of desynchronization were found for the sample of older children. The observation condition revealed significant mu rhythm suppression effects solely for the parietal leads (See Fig. 2). Even though the figure shows that the mu rhythm desynchronization is greater for older participants, the variance analysis revealed no significant age differences. It is of interest that the condition of the repeated execution of movements demonstrated even more pronounced and widely spread mu rhythm suppression, if compared to the first movement condition, with statistically significant interaction effect between the condition and age group factors (See Fig. 3). A significant decrease in the mu rhythm amplitude is discovered at the F3, Fz and Cz electrode sites for the group of younger schoolchildren and at the Fz and C4 electrode sites for the group of adolescents. The imitation condition, relative to one's own movements, had an additional suppression effect of the individual mu rhythm only in the group of adolescents. Significant suppression was discovered in the parietal leads P3 and Pz (See Fig. 4). The condition of the auditory recognition of the computer mouse movement sounds showed significant suppression of the mu rhythm only in the group of adolescents, as well. The suppression was found in the parietal leads P3, Pz and P4 (See Fig. 5). Since the eyes were closed for the two conditions to be compared, we could effectively limit the effects of visual attention modulations which are typically followed by a considerable occipital alpha rhythm desynchronization. As a result, the discovered effects cannot be explained by a mere process of a visual-motor integration but rather by a possible activation of the mirror neuron system parietal component which is thought by some authors to mediate one's action goal coding when observing actions performed by others. Regarding the mu rhythm reactivity in general, the results of the present study showed that the desynchronization of the individually determined EEG mu rhythm becomes more pronounced with age. Reaching the puberty seems to change significantly the reactivity patterns of the mu rhythm. The paper contains 5 Figures and 52 References.

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