title: Subcortical structures in humans can be facilitated by transcranial direct current stimulation.
abstract: Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that alters cortical excitability. Interestingly, in recent animal studies facilitatory effects of tDCS have also been observed on subcortical structures. Here, we sought to provide evidence for the potential of tDCS to facilitate subcortical structures in humans as well. Subjects received anodal-tDCS and sham-tDCS on two separate testing days in a counterbalanced order. After stimulation, we assessed the effect of tDCS on two responses that arise from subcortical structures; (1) wrist and ankle responses to an imperative stimulus combined with a startling acoustic stimulus (SAS), and (2) automatic postural responses to external balance perturbations with and without a concurrent SAS. During all tasks, response onsets were significantly faster following anodal-tDCS compared to sham-tDCS, both in trials with and without a SAS. The effect of tDCS was similar for the dominant and non-dominant leg. The SAS accelerated the onsets of ankle and wrist movements and the responses to backward, but not forward perturbations. The faster onsets of SAS-induced wrist and ankle movements and automatic postural responses following stimulation provide strong evidence that, in humans, subcortical structures--in particular the reticular formation--can be facilitated by tDCS. This effect may be explained by two mechanisms that are not mutually exclusive. First, subcortical facilitation may have resulted from enhanced cortico-reticular drive. Second, the applied current may have directly stimulated the reticular formation. Strengthening reticulospinal output by tDCS may be of interest to neurorehabilitation, as there is evidence for reticulospinal compensation after corticospinal lesions.
authors.affiliation: Radboud University Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Rehabilitation, Nijmegen, The Netherlands.
authors.forename: Jorik
authors.initials: J
authors.lastname: Nonnekes
authors.affiliation: Radboud University Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Rehabilitation, Nijmegen, The Netherlands.
authors.forename: Anass
authors.initials: A
authors.lastname: Arrogi
authors.affiliation: Radboud University Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Neurology/Clinical Neurophysiology, Nijmegen, The Netherlands.
authors.forename: Moniek A M
authors.initials: MA
authors.lastname: Munneke
authors.affiliation: Department of Biomechanical Engineering, MIRA, University of Twente, Enschede, The Netherlands.
authors.forename: Edwin H F
authors.initials: EH
authors.lastname: van Asseldonk
authors.affiliation: Radboud University Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Neurology/Clinical Neurophysiology, Nijmegen, The Netherlands.
authors.forename: Lars B
authors.initials: LB
authors.lastname: Oude Nijhuis
authors.affiliation: Radboud University Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Rehabilitation, Nijmegen, The Netherlands; Sint Maartenskliniek Research, Development & Education, Nijmegen, The Netherlands.
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Geurts
authors.affiliation: Radboud University Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Rehabilitation, Nijmegen, The Netherlands; Sint Maartenskliniek Research, Development & Education, Nijmegen, The Netherlands.
authors.forename: Vivian
authors.initials: V
authors.lastname: Weerdesteyn
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology; D011930:Reaction Time; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D014953:Wrist; D055815:Young Adult