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The prolonged cortical silent period in patients with Huntington's disease
N Modugno1, A Currà, M Giovannelli
1Dipartimento di Scienze Neurologiche, Università di Roma 'La Sapienza', Viale dell'Università 30, 00185, Rome, Italy.
Objectives:
In a group of patients with Huntington's disease and age-matched controls, we studied the cortical silent period (SP) elicited by single transcranial magnetic stimulation (TMS) pulses.
Methods:
We measured the area of the pre-stimulus electromyographic (EMG) activity, the area of the motor evoked potentials (MEPs) and the duration of the SP induced by stimuli delivered at an intensity of 150% of motor threshold with a round coil placed over the vertex. We determined the cortical SP by sampling only the 5 traces containing the shortest SPs and by collecting 10 consecutive unselected traces without selecting trials.
Results:
Patients and controls had normal EMG background areas, and MEP latencies and areas. Whereas data measured from selected trials gave a normal duration of the SP (patients, 154+/-58 ms; controls, 166+/-22 ms), data from unselected trials yielded a significantly longer SP duration in patients than in controls (356+/-251 vs. 159+/-44 ms) and also a larger variance and range.
Conclusions:
We conclude that in Huntington's disease, an abnormal cortical SP is best sought by collecting unselected consecutive traces. We suggest that the prolonged SP in HD originates from a dysfunction of the mechanisms controlling the restart of voluntary movement after TMS.