The significance of coherence estimates in determining central alpha and mu activities

Abstract

Mu activity is characterized by low voltage, is often superimposed on alpha activity and is strongly dependent on the degree of vigilance. Therefore, it is difficult to identify it visually and until recently it was only reported in 10% of subjects. Twenty-six subjects with mu waves were tested here to determine to what extent computing the coherence function between mu and alpha waves could overcome the difficulties in visual evaluation and be used to detect mu waves. Under certain conditions of motor activity, there was a significant change in alpha coherence if mu waves had previously been present. Using these changes in alpha coherence with motor activity, the presence of activity could thus be ascertained. A second group of 54 subjects, who were not known to be mu carriers, were examined by means of visual evaluation and by calculation of the coherence function. In approximately 60% of the subjects, mu waves could be identified. In addition, it was demonstrated that mu and alpha waves are similar in their physiological characteristics. Problem solving activities and field-specific stimuli suppress mu and alpha waves. Similarly, the reactions of both to fluctuations in vigilance are comparable. These similarities and the fact that they probably occur more frequently than previously assumed allow the assumption that mu rhythm represents the ‘resting activity of the central region’.