Changes in the Mu Rhythm in Different Types of Motor Activity and on Observation of Movements

Abstract

A complex study of the characteristics of the mu rhythm with subjects in different states was performed: during observation of movements and during execution of their own movements. Stimuli for movement observation were presented on a monitor screen and consisted of a set of movements for which published data show that mirror neurons mount different responses. In particular, these are movements with or without an expressed goal and various tool manipulations. Studies of the effects of the subjects’ movements on the mu rhythm were performed using situations in which subjects executed their own movements and situations in which they imitated movements seen on a monitor screen. Different methods of processing EEG traces and analyzing evoked desynchronization (suppression) of the mu rhythm were used. These experiments showed that presentation of video recordings of different types of movements induced moderate suppression of the spectral power of the mu rhythm. There were no significant differences in the depression of the mu rhythm on observation of movements performed with or without a clear movement goal or movements for which the goal was reached with a tool. Thus, changes in the mu rhythm and suppression of the mirror neuron system on observation of an executed movement were significantly different. Analysis of the time development of mu rhythm depression showed that changes which were quite clearly apparent at the beginning of observation gradually weakened, generally decreasing to statistically insignificant values at the final stages. The “habituation” effect seen in changes in the mu rhythm indicates a possible role for the mechanisms of involuntary and voluntary attention in mu rhythm depression. The “habituation” effect was also characteristic of more marked changes in the mu rhythm seen on execution of movements by the subjects. Significant differences were seen between depression of the mu rhythm evoked by the subjects’ own movements and on imitation of movements. The habituation effect was more marked in the latter case. These differences in the nature of mu rhythm depression may be associated with differences in activation of those areas of the cortex responsible for movement preparation and programming and with changes associated with the rapid development of motor automation.