title: Facilitatory effect on the motor cortex by electrical stimulation over the cerebellum in humans.
abstract: Electrical stimulation over the cerebellum is known to transiently suppress the contralateral motor cortex in humans. However, projections from the cerebellar nuclei to the primary motor cortex are disynaptic excitatory pathways through the ventral thalamus. In the present investigation we studied facilitatory effects on the motor cortical excitability elicited by electrical stimulation over the cerebellum by recording surface electromyographic (EMG) responses from the first dorsal interosseous (FDI) muscle in nine normal volunteers. For primary motor cortical activation magnetic stimuli were given over the contralateral hand motor area with a figure-of-eight shaped coil with a current to preferentially elicit I3-waves (test stimulus). For cerebellar stimulation high-voltage electric stimuli were given with an anode on the ipsilateral mastoid process and a cathode over the contralateral process as previously described (conditioning stimulus). The effect of conditioning-test interstimulus intervals was investigated. Anodal cerebellar stimuli increased the size of EMG responses to magnetic cortical stimulation at an interstimulus interval of 3 ms. Reversing the current of conditioning stimulus abolished the facilitation. The same (anodal) conditioning stimuli did not affect electrically evoked cortical responses. Based on the effective polarity of the conditioning stimulus and the time course of facilitation we consider that this effect is due to motor cortical facilitation elicited by activation of the excitatory dentatothalamocortical pathway at the deep cerebellar nuclei or superior cerebellar peduncle. We conclude that the motor cortical facilitation is evoked by cerebellar stimulation in humans.
authors.affiliation: Department of Neurology, Division of Neuroscience, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-8655, Tokyo, Japan.
authors.forename: Nobue Kobayashi
authors.initials: NK
authors.lastname: Iwata
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Hanajima
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Furubayashi
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Terao
authors.forename: Haruo
authors.initials: H
authors.lastname: Uesugi
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Shiio
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Enomoto
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Mochizuki
authors.forename: Ichiro
authors.initials: I
authors.lastname: Kanazawa
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ugawa
mesh_terms: D000328:Adult; D002531:Cerebellum / Q000502:physiology*; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology