title: The association of motor imagery and kinesthetic illusion prolongs the effect of transcranial direct current stimulation on corticospinal tract excitability.
abstract: BACKGROUND
  A kinesthetic illusion induced by a visual stimulus (KI) can produce vivid kinesthetic perception. During KI, corticospinal tract excitability increases and results in the activation of cerebral networks. Transcranial direct current stimulation (tDCS) is emerging as an alternative potential therapeutic modality for a variety of neurological and psychiatric conditions, such that identifying factors that enhance the magnitude and duration of tDCS effects is currently a topic of great scientific interest. This study aimed to establish whether the combination of tDCS with KI and sensory-motor imagery (MI) induces larger and longer-lasting effects on the excitability of corticomotor pathways in healthy Japanese subjects.
  
  
  METHODS
  A total of 21 healthy male volunteers participated in this study. Four interventions were investigated in the first experiment: (1) anodal tDCS alone (tDCSa), (2) anodal tDCS with visually evoked kinesthetic illusion (tDCSa + KI), (3) anodal tDCS with motor imagery (tDCSa + MI), and (4) anodal tDCS with kinesthetic illusion and motor imagery (tDCSa + KIMI). In the second experiment, we added a sham tDCS intervention with kinesthetic illusion and motor imagery (sham + KIMI) as a control for the tDCSa + KIMI condition. Direct currents were applied to the right primary motor cortex. Corticospinal excitability was examined using transcranial magnetic stimulation of the area associated with the left first dorsal interosseous.
  
  
  RESULTS
  In the first experiment, corticomotor excitability was sustained for at least 30 min following tDCSa + KIMI (p < 0.01). The effect of tDCSa + KIMI on corticomotor excitability was greater and longer-lasting than that achieved in all other conditions. In the second experiment, significant effects were not achieved following sham + KIMI.
  
  
  CONCLUSIONS
  Our results suggest that tDCSa + KIMI has a greater therapeutic potential than tDCS alone for inducing higher excitability of the corticospinal tract. The observed effects may be related to sustained potentiation of resultant cerebral activity during combined KI, MI, and tDCSa.
authors.affiliation: Laboratory of Sensory Motor Science and Sports Neuroscience, First Division of Physical Therapy, Sapporo Medical University, West 17- South 1, Chuo-ku, Sapporo City, Japan. f-kaneko@sapmed.ac.jp.|Development Research Group for Advanced Neuroscience-based Rehabilitation, Sapporo Medical University, West 17- South 1, Chuo-ku, Sapporo City, Japan. f-kaneko@sapmed.ac.jp.
authors.forename: Fuminari
authors.initials: F
authors.lastname: Kaneko
authors.affiliation: Laboratory of Sensory Motor Science and Sports Neuroscience, First Division of Physical Therapy, Sapporo Medical University, West 17- South 1, Chuo-ku, Sapporo City, Japan.|Development Research Group for Advanced Neuroscience-based Rehabilitation, Sapporo Medical University, West 17- South 1, Chuo-ku, Sapporo City, Japan.
authors.forename: Eriko
authors.initials: E
authors.lastname: Shibata
authors.affiliation: Laboratory of Sensory Motor Science and Sports Neuroscience, First Division of Physical Therapy, Sapporo Medical University, West 17- South 1, Chuo-ku, Sapporo City, Japan.|Division of Health Science Education, School of General Education, Shinshu University, Asahi 3-1-1, Matsumoto City, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hayami
authors.affiliation: Laboratory of Sensory Motor Science and Sports Neuroscience, First Division of Physical Therapy, Sapporo Medical University, West 17- South 1, Chuo-ku, Sapporo City, Japan.|Noboribetsu Hospital, Noboribetsuonsencho133, Noboribetsu City, Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Nagahata
authors.affiliation: Laboratory of Sensory Motor Science and Sports Neuroscience, First Division of Physical Therapy, Sapporo Medical University, West 17- South 1, Chuo-ku, Sapporo City, Japan.|Department of Physical Therapy, Ibaraki Prefectural University of Health Sciences, 4669-2, Ami, Ami-machi, Inashiki-gun, Ibaraki, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Aoyama
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology; D006801:Humans; D007088:Illusions / Q000502:physiology*; D007092:Imagination / Q000502:physiology*; D007699:Kinesthesis / Q000502:physiology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Corticospinal tract; Kinesthetic illusion; Motor imagery; Transcranial direct current stimulation; Transcranial magnetic stimulation; Visual stimulation