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I18 The Use Of Transcranial Magnetic Stimulation In Mapping Cortical Excitability And Inhibition In Huntington’s Disease
  1. AL Philpott1,
  2. PB Fitzgerald2,
  3. TDR Cummins1,
  4. A Churchyard3,
  5. N Georgiou-Karistianis1
  1. 1School of Psychological Sciences, Monash University, Clayton, Melbourne, Australia
  2. 2Monash Alfred Psychiatry Research Centre, Central Clinical School, Monash University, Melbourne, Australia
  3. 3Department of Neurology, Monash Medical Centre, Clayton, Melbourne, Australia

Abstract

Background A better understanding of pathophysiological abnormalities in key cortico-subcortical pathways in Huntington’s disease (HD) will enhance our understanding of the causal relationships between the gene mutation and symptomatology during disease progression.

Aims Transcranial magnetic stimulation (TMS), with a paired-pulse paradigm, was used to assess cortical excitability and inhibition in eight individuals with early symptomatic HD (symp-HD; mean age=56.0 years), twelve individuals with premanifest HD (pre-HD; mean age=41.5 years), and eight healthy controls (mean age=43.1 years).

Methods Following TMS to left motor cortex, electromyographic (EMG) responses were recorded from the right abductor pollicis brevis muscle at rest. Amplitudes of motor-evoked potentials (MEPs), after paired-pulse stimulation, were compared to MEPs elicited by single pulses, and the degree of inhibition was calculated.

Results Resting motor threshold was significantly lower in pre-HD compared with symp-HD and controls, whereas symp-HD did not differ from controls. Symp-HD individuals had significantly reduced short-interval cortical inhibition (SICI) compared with pre-HD and controls, whereas pre-HD did not differ from controls. Further, investigation of the relationship between these electrophysiological indices and neurocognitive measures revealed that for pre-HD and symp-HD individuals, the degree of SICI was significantly correlated with finger tapping performance.

Conclusions These findings suggest very early pathophysiological changes during the premanifest stages of HD. In pre-HD, increased cortical excitability may be an early compensatory response to the neurodegenerative changes in cortico-striatal circuits. Our preliminary data suggest that TMS-EMG may be a sensitive tool for teasing apart the compensatory response observed during the premanifest stages of HD.

KeyWords
  • Premanifest Huntington’s disease
  • Transcranial magnetic stimulation
  • Cortical inhibition

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