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November 1997

Subcortical Reflex Myoclonus?-Reply

Author Affiliations

Department of Neurology University of Turin School of Medicine Ospedale Maggiore 28100 Novara Turin, Italy

Arch Neurol. 1997;54(11):1324. doi:10.1001/archneur.1997.00550230006005

In reply  The interesting letter by Ugawa possibly gives us a chance to emphasize some of the points that actually appeared in our article.1First, Ugawa thinks that the myoclonus seen in our patients was produced by a large descending volley along the corticospinal tract. This would explain the short myoclonus latency. However, a large descending volley should have produced a large electromyographic potential,2 while we verified that the myoclonic electromyographic potential was much smaller (6%-7% of the maximum M wave) than the magnetic or electrical motor evoked potentials having the shortest latency. These motor evoked potentials were 30% to 40% of the maximum M wave. Indeed, it was just the small size of the myoclonic potential that led us to reflect about its conduction time from the cortex to the muscle.Second, Ugawa states that the onset of the N20 wave is the correct marker of the

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