Effects of finger tapping frequency on regional homogeneity of sensorimotor cortex.

Resting-state functional magnetic resonance imaging (RS-fMRI) has been widely used to investigate temporally correlated fluctuations between distributed brain areas, as well as to characterize local synchronization of low frequency (<0.1 Hz) spontaneous fMRI signal. Regional homogeneity (ReHo) was proposed as a voxel-wise measure of the synchronization of the timecourses of neighboring voxels and has been used in many studies of brain disorders. However, the interpretation of ReHo remains challenging because the effect of high frequency task on ReHo is still not clear. In order to investigate the effect of a high-frequency task on the modulation of local synchronization of resting-state activity, we employed three right-finger movement scanning sessions: slow-event related ('Slow'), fast-event related ('Fast'), and continuous finger pressure ('Tonic'), from 21 healthy participants and compared the ReHo of the three task states with that of resting-state ('Rest'). In the contralateral sensorimotor cortex, 'Slow' task state showed greater ReHo than 'Rest' in low frequency band (0-0.08Hz) fMRI signal, but lower ReHo in high frequency band (0.08-1.67 Hz); 'Fast' task state showed lower ReHo than 'Rest' in both the low and high frequency band; 'Tonic' state did not show any significant difference compared to 'Rest'. The results in the contralateral sensorimotor cortex suggest that local synchronization of BOLD signal varies with different finger tapping speed. In the ipsilateral sensorimotor cortex, all the three task states had lower ReHo than the 'Rest' state both in the low and high frequency, suggesting a similar effect of fast and slow finger tapping frequencies on local synchronization of BOLD signal in the ipsilateral motor cortex.