S153. Changes of triad-conditioning facilitation in various neurological disorders

Abstract

Recently, we have reported a triad-conditioning transcranial magnetic stimulation technique (TMS). In this technique, the intercortical facilitation is induced by 40 Hz (interval 25 ms) triad-conditioning stimulation in healthy volunteers, which may reflect the intrinsic rhythm of the primary motor cortex (M1). We used this method to study some changes in M1 in various neurological disorders. Participants were 7 cortical myoclonus, 13 Parkinson’s disease (PD), 13 amyotrophic lateral sclerosis (ALS), 5 focal dystonia and 14 healthy volunteers. Three conditioning stimuli over the primary motor cortex at an intensity of 110% active motor threshold preceded the supra-threshold test TMS at various inter-stimulus intervals corresponding to 10–200 Hz. Amplitude of conditioned motor evoked potentials (MEPs) was compared with the unconditioned MEPs. The facilitation by 40 Hz (gamma rhythm) triad-conditioning TMS observed in healthy volunteers was absent in patients with cortical myoclonus and PD, and reduced in ALS. Normal facilitation was induced in focal dystonia. In cortical myoclonus, facilitation was induced by 25 Hz (beta rhythm) conditioning stimulation. In PD, suppression was induced by 20–33 Hz (beta rhythm) conditioning stimuli. The changes in the triad conditioning facilitation shown above may be explained as follows. In cortical myoclonus, beta rhythms (25 Hz) is probably more preferential than gamma rhythms (40 Hz) due to dysfunction of inhibitory interneurons. The suppression in PD may be explained by abnormal beta rhythm itself. The reduction of 40 Hz triad facilitation may be explained by output cell dysfunction without any rhythm changes in ALS. This technique should give some new additional information about the motor cortical excitability changes in humans.