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Brain Advance Access originally published online on March 17, 2005
Brain 2005 128(6):1292-1300; doi:10.1093/brain/awh473
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© The Author (2005). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please e-mail: journals.permissions@oupjournals.org

Excitability of motor cortex inhibitory circuits in Tourette syndrome before and after single dose nicotine

M. Orth1,2, B. Amann2, M. M. Robertson2 and J. C. Rothwell1

1 Sobell Department of Motor Neuroscience and Movement Disorders and 2 Department of Neuropsychiatry, The National Hospital for Neurology and Neurosurgery, Royal Free and University College Medical School, Queen Square, London WC1N 3BG, UK

Correspondence to: Dr M. Orth, The National Hospital of Neurology and Neurosurgery, Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, Box 77, Queen Square, London WC1N 3BG, UK E-mail: m.orth{at}ion.ucl.ac.uk

The pathophysiology underlying the involuntary tics of Gilles de la Tourette syndrome (GTS) remains unknown. Here we used transcranial magnetic stimulation (TMS) to examine the excitability of two different inhibitory systems in the human motor cortex: short interval intracortical inhibition (SICI) and short interval afferent inhibition (SAI) in 10 healthy non-smoking controls and eight untreated non-smoking patients with GTS. Compared with the healthy control group, both SICI (measured at a range of conditioning intensities) and SAI were reduced in patients. This is consistent with the suggestion that reduced excitability of cortical inhibition is one factor that contributes to the difficulty that patients have in suppressing involuntary tics. In addition, the reduced SAI indicates that impaired intracortical inhibition may not be limited to the motor cortex but also involves circuits linking sensory input and motor output. A single dose of nicotine reduced tic severity as assessed by blind video scoring in the majority of patients. In addition, it abolished the difference between patients and controls in SICI and SAI. There was no effect of nicotine, and no difference between controls and patients in measures of motor or SICI threshold. This indicates that cholinergic input can modulate the efficiency of SICI and SAI differently in GTS and healthy controls.


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