Functional relationship between human rolandic oscillations and motor cortical excitability: an MEG study

Synchronization and desynchronization of the neural rhythm in the brain play an important role in the orchestration of perception, motor action and conscious experience. Based on the results of electrocorticographic and magnetoencephalographic (MEG) recordings, it has been considered that human rolandic oscillations originate in the anterior bank of the central sulcus (20‐Hz rhythm) and the postcentral cortex (10‐Hz rhythm): the 20‐Hz oscillation is closely related to motor function, while the 10‐Hz rhythm is attributed mainly to sensory function. To test whether the rolandic oscillations are functionally relevant to the motor cortical excitability, we examined effects of 1‐Hz repetitive transcranial magnetic stimulation (rTMS) of the left primary motor cortex (M1) on movement‐related changes of the rolandic oscillations in 12 normal subjects. MEG data recorded during brisk extension of the right index finger in two different sessions (with and without rTMS conditioning) were compared. Motor‐evoked potential (MEP) of the right hand muscle was also measured before and after rTMS to assess the motor cortical excitability. We found that 1‐Hz rTMS over M1 significantly reduced the movement‐related rebound of the 20‐Hz oscillation in association with decreased motor cortical excitability. In particular, movement‐related rebound of the 20‐Hz rhythm was closely tied with motor cortical excitability. These findings further strengthen the notion of functional relevance of 20‐Hz cortical oscillation to motor cortical excitability. In the framework of previous studies, the decrease in movement‐related rebound may be regarded as a compensatory reaction to the inhibited cortical activity.