P221 Cerebellar theta burst stimulation modulates the neural activity of interconnected parietal and motor areas.

Question Voluntary movement control and execution are regulated by the influence of the cerebellar output over different interconnected cortical areas, through dentato-thalamo connections. However, in humans, connectivity and plasticity dynamics of the cerebellar-thalamo-cortical connections have been only indirectly explored. Methods In the present study we applied in a group of healthy volunteers transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to directly assess the effects of three theta-burst stimulation (TBS) protocols (intermittent, continuous and sham) over the primary motor cortex (M1) and the posterior parietal cortex (PPC) of the contralateral hemisphere. Results We found a TBS-dependent bidirectional modulation over TMS-evoked activity; specifically, cTBS increased whereas iTBS decreased activity between 100 and 200 ms after TMS, in a similar manner over both M1 and PPC areas. On the oscillatory domain, TBS induced specific changes over M1 natural frequencies of oscillation: TMS-evoked alpha activity was decreased by cTBS whereas beta activity was enhanced by iTBS. No effects were observed after sham stimulation. Conclusions Our data provide novel evidence showing that the cerebellum exerts its control on the cortex likely by impinging on specific set of interneurons dependent on GABA-ergic activity. We show that cerebellar TBS modulates cortical excitability of distant interconnected cortical areas by acting through common temporal, spatial and frequency domains. [ABSTRACT FROM AUTHOR]