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Brain Advance Access published online on March 17, 2005
Brain, 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 email: journals.permissions@oupjournals.org
Received August 23, 2004
Revised December 8, 2004
Accepted January 29, 2005

Article

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

M. Orth 1*, B. Amann 2, M. M. Robertson 2, and J. C. Rothwell 3

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

* To whom correspondence should be addressed.
M. Orth, E-mail: m.orth{at}ion.ucl.ac.uk


  Abstract

Summary 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.

Keywords: transcranial magnetic stimulation; tic treatment; Gilles de la Tourette syndrome; intracortical inhibition; sensory afferent inhibition.
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