Response: "Commentary: Duration dependent effects of the BDNF Val66Met polymorphism on anodal tDCS induced motor cortex plasticity in older adults: a group and individual perspective"
Citation: Puri R and Hinder MR (2016) Response: " Commentary: Duration dependent effects of the BDNF Val66Met polymorphism on anodal tDCS induced motor cortex plasticity in older adults: a group and individual perspective " In a commentary on our recent paper (Puri et al. 2015) Shpektor et al. (2015) provide alternative interpretations on the effects of the BDNF Val66Met polymorphism on transcranial direct current stimulation (tDCS) induced plasticity in older adults. Here we respond to several key issues raised in regard to our findings, and discuss broader implications for the field of non invasive brain stimulation (NBS) Shpektor et al. (2015) suggest that our findings, whereby older Met carriers (homozygous or heterozygous for the Met allele) exhibit a greater plastic response to 20 min of anodal tDCS compared to Val/Val homozygotes, may be seen as " controversial " as we reported an influence of the BDNF Val66Met polymorphism on plasticity at rest (i.e. not during task performance) However, a broader search of the extant literature suggests that the effects of the BDNF Val66Met polymorphism on tDCS induced plasticity are varied, even before one considers the interaction of tDCS effects with neural activation resulting from performing a concurrent motor task (e.g. Fritsch et al. 2010) Specifically, Antal et al. (2010) reported a significant Genotype x Time interaction where greater motor evoked potential (MEP) amplitude was observed in Met allele carriers compared to Val/Val homozygotes at 25 and 60 min following anodal tDCS. Furthermore, Teo et al. (2014) reported a significant facilitation in MEPs post anodal stimulation only for Met carriers and not Val/Val homozygotes. Recently, Strube et al. (2015) reported a greater increase in MEPs for healthy Met carriers than Val/Val homozygotes after anodal tDCS (although this did not quite reach the a priori level of statistical significance, p 0.072, it was associated with a large effect size, d 0.799) On the other hand, some studies do not report statistically significant differences between Met carriers and Val/Val homozygotes (Cheeran et al. 2008; Di Lazzaro et al. 2012; Fujiyama et al. 2014) However, as we alluded to in our paper, an absence of statistically significant effects should be interpreted with caution, especially when sample Puri and Hinder BDNF, Cortical Plasticity, and Aging sizes are small and studies are not primarily designed to investigate BDNF polymorphism effects (e.g. Fujiyama et al. 2014) In addition, there appears to be some preliminary evidence to suggest that the specific
Front. Aging Neurosci.