title: Duration-dependent effects of the BDNF Val66Met polymorphism on anodal tDCS induced motor cortex plasticity in older adults: a group and individual perspective.
abstract: The brain derived neurotrophic factor (BDNF) Val66Met polymorphism and stimulation duration are thought to play an important role in modulating motor cortex plasticity induced by non-invasive brain stimulation (NBS). In the present study we sought to determine whether these factors interact or exert independent effects in older adults. Fifty-four healthy older adults (mean age = 66.85 years) underwent two counterbalanced sessions of 1.5 mA anodal transcranial direct current stimulation (atDCS), applied over left M1 for either 10 or 20 min. Single pulse transcranial magnetic stimulation (TMS) was used to assess corticospinal excitability (CSE) before and every 5 min for 30 min following atDCS. On a group level, there was an interaction between stimulation duration and BDNF genotype, with Met carriers (n = 13) showing greater post-intervention potentiation of CSE compared to Val66Val homozygotes homozygotes (n = 37) following 20 min (p = 0.002) but not 10 min (p = 0.219) of stimulation. Moreover, Met carriers, but not Val/Val homozygotes, exhibited larger responses to TMS (p = 0.046) after 20 min atDCS, than following 10 min atDCS. On an individual level, two-step cluster analysis revealed a considerable degree of inter-individual variability, with under half of the total sample (42%) showing the expected potentiation of CSE in response to atDCS across both sessions. Intra-individual variability in response to different durations of atDCS was also apparent, with one-third of the total sample (34%) exhibiting LTP-like effects in one session but LTD-like effects in the other session. Both the inter-individual (p = 0.027) and intra-individual (p = 0.04) variability was associated with BDNF genotype. In older adults, the BDNF Val66Met polymorphism along with stimulation duration appears to play a role in modulating tDCS-induced motor cortex plasticity. The results may have implications for the design of NBS protocols for healthy and diseased aged populations.
authors.affiliation: Human Motor Control Laboratory, School of Medicine, Faculty of Health, University of Tasmania, Hobart TAS, Australia.
authors.forename: Rohan
authors.initials: R
authors.lastname: Puri
authors.affiliation: Human Motor Control Laboratory, School of Medicine, Faculty of Health, University of Tasmania, Hobart TAS, Australia.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Hinder
authors.affiliation: Human Motor Control Laboratory, School of Medicine, Faculty of Health, University of Tasmania, Hobart TAS, Australia ; Movement Control and Neuroplasticity Research Group, Department of Kinesiology KU Leuven, Belgium.
authors.forename: Hakuei
authors.initials: H
authors.lastname: Fujiyama
authors.affiliation: School of Health Sciences, Federation University Australia, Ballarat VIC, Australia.
authors.forename: Rapson
authors.initials: R
authors.lastname: Gomez
authors.affiliation: Trinity College Institute of Neuroscience and School of Psychology, Trinity College Dublin Dublin, Ireland ; School of Psychology, Queen's University Belfast Belfast, UK.
authors.forename: Richard G
authors.initials: RG
authors.lastname: Carson
authors.affiliation: Human Motor Control Laboratory, School of Medicine, Faculty of Health, University of Tasmania, Hobart TAS, Australia ; Research Institute for Sport and Exercise Sciences, Liverpool John Moores University Liverpool, UK.
authors.forename: Jeffery J
authors.initials: JJ
authors.lastname: Summers
keywords: BDNF; Val66Met polymorphism; corticospinal excitability; motor cortex; older adults; plasticity; transcranial direct current stimulation (tDCS); transcranial magnetic stimulation (TMS)