Temporal Lobe Cortical Electrical Stimulation during the Encoding and Retrieval Phase Reduces False Memories Paulo S. Boggio2*, Felipe Fregni1*, Claudia Valasek2, Sophie Ellwood3, Richard Chi3, Jason Gallate3, Alvaro Pascual-Leone1, Allan Snyder3 1 Berenson-Allen Center for Noninvasive Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, United States of America, 2 Cognitive Neuroscience Laboratory and Developmental Disorders Program, Center for Health and Biological Sciences, Mackenzie Presbyterian University, Sao Paulo, Brazil, 3 Centre for the Mind, University of Sydney, Sydney, Australia Abstract A recent study found that false memories were reduced by 36% when low frequency repetitive transcranial magnetic stimulation (rTMS) was applied to the left anterior temporal lobe after the encoding (study) phase. Here we were interested in the consequences on a false memory task of brain stimulation throughout the encoding and retrieval task phases. We used transcranial direct current stimulation (tDCS) because it has been shown to be a useful tool to enhance cognition. Specifically, we examined whether tDCS can induce changes in a task assessing false memories. Based on our preliminary results, three conditions of stimulation were chosen: anodal left/cathodal right anterior temporal lobe (ATL) stimulation (‘‘bilateral stimulation’’); anodal left ATL stimulation (with a large contralateral cathodal electrode – referred as ‘‘unilateral stimulation’’) and sham stimulation. Our results showed that false memories were reduced significantly after the two active conditions (unilateral and bilateral stimulation) as compared with sham stimulation. There were no significant changes in veridical memories. Our findings show that false memories are reduced by 73% when anodal tDCS is applied to the anterior temporal lobes throughout the encoding and retrieval stages, suggesting a possible strategy for improving certain aspects of learning. Citation: Boggio PS, Fregni F, Valasek C, Ellwood S, Chi R, et al. (2009) Temporal Lobe Cortical Electrical Stimulation during the Encoding and Retrieval Phase Reduces False Memories. PLoS ONE 4(3): e4959. doi:10.1371/journal.pone.0004959 Editor: Bernhard Baune, James Cook University, Australia Received December 18, 2008; Accepted February 26, 2009; Published March 25, 2009 Copyright: 2009 Boggio et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: There was limited partial support to this study - from (i) Harvard Club of Australia foundation that funded the trip of F.F. to A.S. laboratory as to finalize this paper and (2) support for research assistant from CNPQ - Brazilian funding agency. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: boggio@mackenzie.br (PSB); ffregni@bidmc.harvard.edu (FF) Introduction In a seminal study, Bartlett noted that memories are not literal representations of the past [1]. Instead, ‘‘facts’’ are unconsciously constructed to fit our schemata [2,3], which can lead to false memories. Whilst constructive memory is an important compo- nent of an efficient healthy memory system, and is important for future planning [4,5], there are obvious benefits if false memories can be reduced temporarily in certain circumstances. To that end a recent study [6] found that false memories are reduced by temporarily disrupting anterior temporal lobe activity, using low frequency magnetic pulse stimulation (rTMS). This area has been implicated in semantic memory and conceptual labeling [7,8,9]. After active stimulation, participants had 36% fewer false memories than they had following sham stimulation, while veridical memory was not affected. This is comparable to the advantage that subjects with autism and semantic dementia – by virtue of a reduction in gist-based memory – show over ‘‘normal’’ individuals [10,11]. In this study, TMS was applied for 15 minutes after the study phase, that is, after the encoding and before the retrieval test phase. In this investigation, we are interested to study the influence of transcranial direct current brain stimulation (tDCS) [12] on false memories when the stimulation is applied continuously, before the encoding as well as during the retrieval test phase. We predicted that the reduction in false memories would be larger if local activity modification is done before encoding phase. tDCS is an attractive tool for this goal as it is a non-invasive, safe method to change membrane resting threshold and modify spontaneous activity [12] and therefore modify information processing effectively [13]. A clue for achieving our goal of reducing false memories comes from patients with left anterior temporal lobe dementia who have autistic-like qualities [14,15,16]. Individuals with autism and temporal lobe dementia are known for being literal [11,16,17,18,19] and less susceptible to false memories [10]. On the other hand, the more concept orientated we are, the more we tend to categorize and the more prone we are to false memories [7,19,20]. The anterior temporal lobes (ATL), especially the left ATL, are vital for semantic processing, being implicated as the region responsible for conceptual knowledge, labels and categories [16,21,22,23]. When the left ATL is damaged, patients lose their semantic memory and their ability to name or label objects, while retaining the ability to retrieve literal details [16,23]. For these reasons, we hypothesized that disruption of ATL activity by tDCS would reduce false memories by diminishing our reliance on gist in encoding and retrieval. PLoS ONE | www.plosone.org 1 March 2009 | Volume 4 | Issue 3 | e4959