title: Anodal Cerebellar Direct Current Stimulation Reduces Facilitation of Propriospinal Neurons in Healthy Humans.
abstract: Coordinated muscle synergies in the human upper limb are controlled, in part, by a neural distribution network located in the cervical spinal cord, known as the cervical propriospinal system. Studies in the cat and non-human primate indicate the cerebellum is indirectly connected to this system via output pathways to the brainstem. Therefore, the cerebellum may indirectly modulate excitability of putative propriospinal neurons (PNs) in humans during upper limb coordination tasks.
  
  
  
  This study aimed to test whether anodal direct current stimulation (DCS) of the cerebellum modulates PNs and upper limb coordination in healthy adults. The hypothesis was that cerebellar anodal DCS would reduce descending facilitation of PNs and improve upper limb coordination.
  
  
  
  Transcranial magnetic stimulation (TMS), paired with peripheral nerve stimulation, probed activity in facilitatory and inhibitory descending projections to PNs following an established protocol. Coordination was tested using a pursuit rotor task performed by the non-dominant (ipsilateral) hand. Anodal and sham DCS were delivered over the cerebellum ipsilateral to the non-dominant hand in separate experimental sessions. Anodal DCS was applied to a control site lateral to the vertex in a third session. Twelve right-handed healthy adults participated.
  
  
  
  Pairing TMS with sub-threshold peripheral nerve stimulation facilitated motor evoked potentials at intensities just above threshold in accordance with the protocol. Anodal cerebellar DCS reduced facilitation without influencing inhibition, but the reduction in facilitation was not associated with performance of the pursuit rotor task.
  
  
  
  The results of this study indicate dissociated indirect control over cervical PNs by the cerebellum in humans. Anodal DCS of the cerebellum reduced excitability in the facilitatory descending pathway with no effect on the inhibitory pathway to cervical PNs. The reduction in PN excitability is likely secondary to modulation of primary motor cortex or brainstem nuclei, and identifies a neuroanatomical pathway for the cerebellum to assist in coordination of upper limb muscle synergies in humans.
authors: Applied Brain Research Laboratory, Discipline of Physiotherapy, Faculty of Health Sciences Flinders University, Adelaide, SA 5041, Australia.
authors: Muhammed
authors: M
authors: Chothia
authors: Discipline of Speech Pathology and Audiology, School of Health Sciences, Flinders University, SA 5041, Australia.
authors: Sebastian
authors: S
authors: Doeltgen
authors: Applied Brain Research Laboratory, Discipline of Physiotherapy, Faculty of Health Sciences Flinders University, Adelaide, SA 5041, Australia; Discipline of Physiotherapy, Graduate School of Health, University of Technology Sydney, NSW, Australia. Electronic address: lynley.bradnam@uts.edu.au.
authors: Lynley V
authors: LV
authors: Bradnam
mesh_terms: D000328:Adult; D002531:Cerebellum / Q000502:physiology*; D004566:Electrodes; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006225:Hand / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology; D009415:Nerve Net / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D011434:Proprioception / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D034941:Upper Extremity / Q000502:physiology; D055815:Young Adult
keywords: Cerebellum; Direct current stimulation; Dystonia; Propriospinal; Stroke; Transcranial magnetic stimulation