Effect of theta burst stimulation on sensorimotor cortex in humans

Objective: To study the after-effect of theta burst transcranial magnetic stimulation (TBS) on sensorimotor cortex excitability as well as cortico-muscular synchronization in humans. Methods: We used a continuous TBS (cTBS) paradigm for 40 sec (600 pulses) (Huang et al., 2005). Somatosensory evoked potentials (SEPs) following electrical stimulation of right or left median nerve and motor evoked potentials (MEPs) in the right or left first dorsal interosseous (FDI) muscles were recorded before and after cTBS over the left motor (M1) or sensory (SI) cortex (2 cm posterior to M1) in healthy subjects. In addition, coherence function was computed as a measure of cortico-muscular synchronization by recording electroencephalogram (EEG) and electromyogram (EMG) during the isometric contraction. Results: Amplitudes of P25/N33 (parietal SEP component) following right median nerve stimulation were significantly increased for at least 53 minutes after cTBS over left M1, whereas this component was suppressed for 13 min after cTBS over left S1. MEPs in right as well as left FDI muscles were suppressed in a similar time course after cTBS over left M1. The beta-band cortico-muscular coherence for the C3 scalp site, significantly decreased in 30-60 minutes after cTBS over left M1. Conclusion: cTBS can induce a long-lasting change in sensorimotor cortex excitability and cortico-muscular synchronization.