Affiliations: Department of Neurology, University of Ulm, Ulm,
Germany | Department of Neurology, University Medical Center
Hamburg Eppendorf, Martinistr, Hamburg, Germany
Note: [] Corresponding author: Dr. Michael Orth, Department of Neurology,
University of Ulm, Oberer Eselsberg 45/1, 89081 Ulm, Germany. Tel.: +49 731
50063095; Fax: +49 731 50063082; E-mail: michael.orth@uni-ulm.de
Abstract: Gilles de la Tourette syndrome (GTS) is a sensorimotor disorder
where the sensitivity to external and internal stimuli might be increased and
unwanted responses to such stimuli cannot be sufficiently suppressed. Transcranial magnetic stimulation (TMS) studies indicate that, at
rest, axonal excitability of cortico-spinal neurons and intra-cortical
inter-neurons was consistently normal in GTS. However, synaptic excitability in
cortico-spinal neurons and the SICI circuit may be lower than normal. In
addition, an electrophysiological marker of sensory motor integration, SAI, was
reduced in the baseline state consistent with reduced efficiency of synaptic
inhibition. Given the possible influence of sensory inputs in triggering the
release of tics reduced SAI may be a direct physiological reflection of
increased access of sensory input to motor output in GTS. Experiments examining
control of voluntary movements revealed that in GTS motor cortex excitability
increases less than in controls when preparing a movement even though
intra-cortical inhibition (i.e. SICI) normalises. In GTS the gain of many motor circuits may be reduced and hence less
sensitive to small changes in input from other areas. These cortical changes
may constitute an adaptive response to abnormal basal ganglia-motor cortex
inputs.
Keywords: Transcranial magnetic stimulation, axon, synapse, sensori-motor integration
