title: The contribution of interindividual factors to variability of response in transcranial direct current stimulation studies.
abstract: There has been an explosion of research using transcranial direct current stimulation (tDCS) for investigating and modulating human cognitive and motor function in healthy populations. It has also been used in many studies seeking to improve deficits in disease populations. With the slew of studies reporting "promising results" for everything from motor recovery after stroke to boosting memory function, one could be easily seduced by the idea of tDCS being the next panacea for all neurological ills. However, huge variability exists in the reported effects of tDCS, with great variability in the effect sizes and even contradictory results reported. In this review, we consider the interindividual factors that may contribute to this variability. In particular, we discuss the importance of baseline neuronal state and features, anatomy, age and the inherent variability in the injured brain. We additionally consider how interindividual variability affects the results of motor-evoked potential (MEP) testing with transcranial magnetic stimulation (TMS), which, in turn, can lead to apparent variability in response to tDCS in motor studies.
authors.affiliation: Department of Advanced Neuroimaging, Integrative Brain Imaging Center, National Center of Neurology and Psychiatry Tokyo, Japan ; Computational, Cognitive and Clinical Neuroimaging Laboratory, Division of Restorative Neurosciences, Imperial College London London, UK.
authors.forename: Lucia M
authors.initials: LM
authors.lastname: Li
authors.affiliation: Department of Advanced Neuroimaging, Integrative Brain Imaging Center, National Center of Neurology and Psychiatry Tokyo, Japan ; Research Fellow of the Japan Society for the Promotion of Science Tokyo Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Uehara
authors.affiliation: Department of Advanced Neuroimaging, Integrative Brain Imaging Center, National Center of Neurology and Psychiatry Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Hanakawa
keywords: cognition; interindividual variability; motor-evoked potential; transcranial direct current stimulation; transcranial magnetic stimulation