Speech Facilitation by Left Inferior Frontal Cortex Stimulation

John C. Rothwell,Mahalekshmi Desikan,Oliver Josephs,Joseph M. Galea,Alex P. Leff,Rachel Holland,Jennifer Crinion,Cathy J. Price

doi:10.1016/j.cub.2011.07.021

Abstract

SummaryElectrophysiological studies in humans and animals suggest that noninvasive neurostimulation methods such as transcranial direct current stimulation (tDCS) can elicit long-lasting [1], polarity-dependent [2] changes in neocortical excitability. Application of tDCS can have significant and selective behavioral consequences that are associated with the cortical location of the stimulation electrodes and the task engaged during stimulation [3–8]. However, the mechanism by which tDCS affects human behavior is unclear. Recently, functional magnetic resonance imaging (fMRI) has been used to determine the spatial topography of tDCS effects [9–13], but no behavioral data were collected during stimulation. The present study is unique in this regard, in that both neural and behavioral responses were recorded using a novel combination of left frontal anodal tDCS during an overt picture-naming fMRI study. We found that tDCS had significant behavioral and regionally specific neural facilitation effects. Furthermore, faster naming responses correlated with decreased blood oxygen level-dependent (BOLD) signal in Broca's area. Our data support the importance of Broca's area within the normal naming network and as such indicate that Broca's area may be a suitable candidate site for tDCS in neurorehabilitation of anomic patients, whose brain damage spares this region.

Highlights

Recent research suggests a relationship between primarily left inferior frontal cortex (IFC) activity, including Broca’s area, and improved naming performance in stroke patients with aphasia [14,15,16,17]
Application of transcranial direct current stimulation (tDCS) can have significant and selective behavioral consequences that are associated with the cortical location of the stimulation electrodes and the task engaged during stimulation [3,4,5,6,7,8]
Functional magnetic resonance imaging has been used to determine the spatial topography of tDCS effects [9,10,11,12,13], but no behavioral data were collected during stimulation

Summary

Introduction

Recent research suggests a relationship between primarily left inferior frontal cortex (IFC) activity, including Broca’s area, and improved naming performance in stroke patients with aphasia [14,15,16,17]. Anodal transcranial direct current stimulation (A-tDCS), a method thought to increase cortical excitability, over Broca’s area has been shown to enhance naming accuracy in aphasic patients [6]. A-tDCS has been proposed as a clinical tool for rehabilitation of specific language function in brain-damaged patients and as a supplementary treatment approach for anomia [15]. A-tDCS of Broca’s area has resulted in (1) an improved rate of verbal fluency [18] and (2) facilitation of language skills when paired with a learning paradigm [3, 4]

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