Brain, Vol. 119, No. 1, 71-77, 1996
© 1996 Oxford University Press
research-article |
Cortical inhibition in Parkinson's disease
A study with paired magnetic stimulation
Dipartimento di Scienze Neurologiche, Università degli Studi di Roma La Sapienza Viale Università 30, 00185 Roma
Correspondence to:
Alfredo Berardelli, MD, Dipartimento di Scienze Neurologiche, Viale Università 30, 00185 Roma, Italy
The activity of motor cortical inhibitory circuits was studied with paired transcranial magnetic stimuli in 16 patients with Parkinson's disease off therapy, five patients off and on therapy, and 11 normal subjects. Paired stimuli were delivered at short (320 ms) as well as long (100250 ms) intervals during slight voluntary contraction. The intensity of the conditioning stimulus was subthreshold (80%) at short, and suprathreshold (150%) at long intervals. In addition, the silent period following a single magnetic shock given at 150% of threshold was measured. With short interstimulus intervals, no significant difference between patients and normal subjects could be detected. With long interstimulus intervals, the test response was significantly more inhibited in patients than in normal subjects. Although the cortical silent period was found to be slightly shorter, the recovery of motor evoked potentials was incomplete in patients with Parkinson's disease. This alteration could be partially reverted by dopaminergic therapy. In conclusion, the responsiveness of motor cortices to suprathreshold magnetic stimuli delivered after the end of the silent period is impaired in patients with Parkinson's disease, possibly due to prolonged activity in intracortical inhibitory circuits. The positive effect of L-dopa suggests that dopaminergic modulation of cortical activity, most probably at basal ganglia level, is involved in the pathogenesis of this phenomenon.
motor cortex; magnetic stimulation; cortical inhibition; Parkinson's disease; dopaminergic system
Received December 24, 1994. Revised June 6, 1995. Accepted September 21, 1995.
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