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1 Schizophrenia Program, Centre for Addiction and Mental Health, Toronto, Ontario, Canada,2 Division of Neurology and Toronto Western Research Institute, University of Toronto, Toronto, Ontario, Canada3Alfred Psychiatry Research Centre, The Alfred and Monash University Department of Psychological Medicine, Commercial Road, Melbourne, Victoria, Australia
Animal studies have shown that cerebellar projections influence both excitatory and inhibitory neurones in the motor cortex but this connectivity has yet to be demonstrated in human subjects. In human subjects, magnetic or electrical stimulation of the cerebellum 5–7 ms before transcranial magnetic stimulation (TMS) of the motor cortex decreases the TMS-induced motor-evoked potential (MEP), indicating a cerebellar inhibition of the motor cortex (CBI). TMS also reveals inhibitory and excitatory circuits of the motor cortex, including a short-interval intracortical inhibition (SICI), long-interval intracortical inhibition (LICI) and intracortical facilitation (ICF). This study used magnetic cerebellar stimulation to investigate connections between the cerebellum and these cortical circuits. Three experiments were performed on 11 subjects. The first experiment showed that with increasing test stimulus intensities, LICI, CBI and ICF decreased, while SICI increased. The second experiment showed that the presence of CBI reduced SICI and increased ICF. The third experiment showed that the interaction between CBI and LICI reduced CBI. Collectively, these findings suggest that cerebellar stimulation results in changes to both inhibitory and excitatory neurones in the human motor cortex.
(Received 15 December 2003;
accepted after revision 19 March 2004;
first published online 26 March 2003)
Corresponding author R. Chen: Toronto Western Hospital, 5 W-445, 399 Bathurst Street, Toronto, Ontario, Canada M5T 2S8. Email: robert.chen{at}uhn.on.ca
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