Background: Word retrieval during verbal fluency tasks invokes both automatic and controlled cognitive processes. A distinction has been made between the generation of words clusters and switches between such clusters on verbal fluency tasks. Clusters, defined by the reporting of contiguous words that constitute semantic or phonemic subcategories, are thought to reflect relatively automatic processing. In contrast, switching from one subcategory to another is thought to require a more controlled, effortful form of cognitive processing. Objective: In this single-blind, sham-controlled experiment, we investigated whether anodal and cathodal transcranial direct current stimulation (tDCS) can differentially modify controlled or automatic processes that support lexical retrieval, as assessed by clustering and switching on verbal fluency tasks, in 24 healthy right-handed adults. Methods: Participants were randomly assigned to receive 1 mA of either anodal (excitatory) or cathodal (inhibitory) active tDCS over the left dorsolateral prefrontal cortex in addition to sham stimulation over the same region in counterbalanced order. Participants engaged in various cognitive activities during the first 23 min of stimulation. Then, during the final segment of each 30-min session, they completed letter- and category-cued word fluency tasks. Results: Participants reported more words on category-cued word fluency tasks during anodal than sham stimulation (25.9 vs. 23.0 words; p = 0.055). They also showed a net increase in the number of clustered words during anodal stimulation compared to a net decrease during cathodal stimulation (1.3 vs. −1.5 words; p = 0.038). Conclusion: tDCS can selectively alter automatic aspects of speeded lexical retrieval in a polarity-dependent fashion during a category-guided fluency task.
Keywords: verbal fluency, clustering, switching, transcranial direct current stimulation
Citation: Vannorsdall TD, Schretlen DJ, Andrejczuk M, Ledoux K, Bosley LV, Weaver JR, Skolasky RL and Gordon B (2012) Altering automatic verbal processes with transcranial direct current stimulation. Front. Psychiatry 3:73. doi: 10.3389/fpsyt.2012.00073
Received: 08 March 2012; Paper pending published: 13 April 2012;
Accepted: 20 July 2012; Published online: 06 August 2012.
Edited by:Alberto Priori, Università di Milano, Italy
Reviewed by:Paul Croarkin, Mayo Clinic, USA
Copyright: © 2012 Vannorsdall, Schretlen, Andrejczuk, Ledoux, Bosley, Weaver, Skolasky and Gordon. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Barry Gordon, The Johns Hopkins University School of Medicine, 1629 Thames Street, Suite 350, Baltimore, MD 21231, USA. e-mail: email@example.com