Event-related Desynchronization Reflects Down-regulation of Intracortical Inhibition in Human Primary Motor Cortex Running Head: Erd Reflects Down-regulation of Intracortical Inhibition

20 There is increasing interest in electroencephalogram (EEG)-based brain-computer interface 21 (BCI) as a tool for rehabilitation of upper limb motor functions in hemiplegic stroke patients. 22 This type of BCI often exploits EEG mu and beta oscillations recorded over the sensorimotor 23 areas, and their event-related desynchronization (ERD) following motor imagery is believed 24 to represent increased sensorimotor cortex excitability. However, it remains unclear whether 25 the sensorimotor cortex excitability is actually correlated with ERD. Thus, we assessed the 26 association of ERD with primary motor cortex (M1) excitability during motor imagery of 27 right wrist movement. M1 excitability was tested by motor evoked potentials (MEPs), 28 short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using 29 transcranial magnetic stimulation (TMS). Twenty healthy participants were recruited. The 30 participants performed 7 seconds of rest followed by 5 seconds of motor imagery, and 31 received online visual feedback of the ERD magnitude of the contralateral hand M1 while 32 performing the motor imagery task. TMS was applied to the right hand M1 when ERD 33 exceeded predetermined thresholds during motor imagery. MEP amplitudes, SICI and ICF 34 were recorded from the agonist muscle of the imagined hand movement. Results showed that 35 the large ERD during wrist motor imagery was associated with significantly increased MEP 36 amplitudes and reduced SICI, but no significant changes in ICF. Thus, ERD magnitude during 37 wrist motor imagery represents M1 excitability. This study provides electrophysiological 38 evidence that motor imagery task involving ERD may induce changes in corticospinal 39