Polarity-specific transcranial direct current stimulation disrupts auditory pitch learning

Robert J. Zatorre,Reiko Matsushita,Jamila Andoh

doi:10.3389/fnins.2015.00174

Abstract

Transcranial direct current stimulation (tDCS) is attracting increasing interest because of its potential for therapeutic use. While its effects have been investigated mainly with motor and visual tasks, less is known in the auditory domain. Past tDCS studies with auditory tasks demonstrated various behavioral outcomes, possibly due to differences in stimulation parameters, task-induced brain activity, or task measurements used in each study. Further research, using well-validated tasks is therefore required for clarification of behavioral effects of tDCS on the auditory system. Here, we took advantage of findings from a prior functional magnetic resonance imaging study, which demonstrated that the right auditory cortex is modulated during fine-grained pitch learning of microtonal melodic patterns. Targeting the right auditory cortex with tDCS using this same task thus allowed us to test the hypothesis that this region is causally involved in pitch learning. Participants in the current study were trained for 3 days while we measured pitch discrimination thresholds using microtonal melodies on each day using a psychophysical staircase procedure. We administered anodal, cathodal, or sham tDCS to three groups of participants over the right auditory cortex on the second day of training during performance of the task. Both the sham and the cathodal groups showed the expected significant learning effect (decreased pitch threshold) over the 3 days of training; in contrast we observed a blocking effect of anodal tDCS on auditory pitch learning, such that this group showed no significant change in thresholds over the 3 days. The results support a causal role for the right auditory cortex in pitch discrimination learning.

Highlights

Transcranial direct current stimulation is a non-invasive technique to modulate cortical excitability (Nitsche et al, 2008; Jacobson et al, 2012)
The participants were randomly divided into three groups of 14 people each: an anodal Transcranial direct current stimulation (tDCS) group received tDCS with the anodal electrode placed over the right temporal cortex, a cathodal tDCS group received tDCS with the cathodal electrode placed over the right temporal cortex, and a sham group received sham tDCS
The baseline thresholds were compared across groups using one-way analysis of variance (ANOVA) and were not significantly different [F(2, 39) = 0.15, p = 0.86], indicating that the random assignment was successful in producing comparable groups prior to stimulation

Summary

Introduction

Transcranial direct current stimulation (tDCS) is a non-invasive technique to modulate cortical excitability (Nitsche et al, 2008; Jacobson et al, 2012). Measurement of motor evoked potentials (MEP) revealed tDCS and auditory learning that anodal tDCS over motor cortex increases cortical excitability and cathodal tDCS decreases it (Nitsche and Paulus, 2000; Nitsche et al, 2003a) and that the effect can last for more than an hour after application of the current with conventional parameters (Nitsche and Paulus, 2001; Nitsche et al, 2003a). Anodal tDCS of M1 enhanced the offline effect of motor learning (Reis et al, 2009), anodal tDCS of V1 blocked overnight consolidation of a visual contrast detection task (Peters et al, 2013), and anodal tDCS applied over the dorsolateral prefrontal cortex enhanced verbal working memory training (Richmond et al, 2014)

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