Methods Study participants Participants were recruited by advertising in flyers and notices distributed throughout local universities. We included healthy participants aged between 18 and 30 years. Participants were excluded if they had any neuropsychiatric disorder, current or past history of alcohol or other drug use, were taking any medication acting on the central nervous system or were pregnant. Thirty participants (mean age of 19.861.16, 20 females) were enrolled in this study. All subjects were undergraduate students, and na¨ıve to the task. Participants gave written informed consent for the study, and approval was obtained from the local research ethics committee (process approval number 0042.0.272.000-07). The study was carried out to conform to the principles of the Declaration of Helsinki. Study protocol Participants were randomized to receive one of the three types of intervention: 1) anodal (+) left anterior temporal lobe/cathodal (2) right anterior lobe (referred in the text as ‘‘bilateral stimulation’’); 2) anodal (+) left anterior temporal lobe/cathodal (2) right anterior lobe – however the size of cathodal electrode in this condition was 100 cm2, a much larger and more diffuse pad than the standard 35 cm2 pad, (referred in the text as ‘‘unilateral stimulation’’); and 3) sham stimulation. Participants and the evaluating investigators (except the investigators that applied tDCS) were blinded to the treatment condition. All stimulation sessions were carried out by the same researchers and at the same time of the day. Cognitive tasks We used the same task as was used in the recent rTMS study [6]; that is, a modified version of Roediger and McDermott’s (1995) paradigm. Participants were instructed to remember three lists of words and told that they would be asked to recognize them later. Each list has a ‘‘theme’’. For example, one list contains words related to bread (e.g. loaf, sandwich, and so forth), but not the word ‘‘bread’’ per se. In selecting categories of stimuli for the false memory task, two criteria were balanced against each other. We chose categories that had reasonably high false recognition rates and contained words that were closely related enough to allow us to select three critical lures (instead of one) whilst leaving nine study words that would establish the category concept. We included three critical lures per category to maintain sufficient power in the test. Piloting confirmed the efficacy of our test in revealing false memories. We asked our participants to memorize a series of 27 words, each presented for three seconds on a computer screen. The words were selected from three different semantic categories (e.g. bread, music and doctor). They were then presented with 27 words in succession and were asked to click ‘yes’ if they had seen the word earlier or ‘no’ if not. Specifically, participants were shown nine ‘‘true’’ words (words that they had seen before), nine ‘‘false’’ words (words that they had not seen before) and nine unrelated words (words they had not seen before and were not related to the categories of words). We then analyzed veridical memory for ‘‘true’’ words (words that were presented previously) and false memories (false positives for critical ‘‘lure’’). This test was performed during and after stimulation with an interval between the recognition phases of approximately 10 minutes. Transcranial direct current stimulation Direct current was transferred by a saline-soaked pair of surface sponge electrodes and delivered by a specially developed, battery- driven, constant current stimulator with a maximum output of tDCS Reduces False Memories 10 mA. We used electrodes of two different sizes: for the anode (+) electrode, we used a sponge of 35 cm2 [12], for the cathode (2) electrode we used the conventional 35 cm2 electrode and also a larger electrode of 100 cm2 as it has been shown that this large electrode induces a small and nonsignificant effect on cortical activity [24]. The latter electrode configuration was designed to perform a functional monopolar anodal tDCS without relevantly shifting excitability of the contralateral temporal lobe by the cathodal, reference electrode (figure 1). As aforementioned, participants were randomized to receive three different types of treatment: 1) 2) 3) Anodal stimulation of the left temporal cortex and cathodal stimulation of the right temporal cortex (referred in the text as ‘‘bilateral stimulation’’). The anode electrode was placed over T3 (using the EEG International 10/20 System) and the cathode electrode over T4. For this condition we used two electrodes of 35 cm2. Anodal stimulation of the left anterior temporal lobe and cathodal stimulation of the right anterior lobe – however the cathodal electrode was 100 cm2 (referred in the text as ‘‘unilateral stimulation’’). The anode electrode was placed over T3 (using EEG 10/20 system) and the cathode electrode over T4. Sham stimulation. For sham stimulation, the electrodes were placed in the same positions as in active stimulation; however, the stimulator was turned off after 30 seconds of stimulation. Therefore, the participants felt the initial itching sensation associated with turning on the device, but received no current stimulation for the rest of the treatment period. A recent study showed that this method of sham stimulation reliably convinces the participant they are receiving active stimulation [25 2006]. The rationale for choosing the anterior temporal lobe (ATL) is because this area, especially the left ATL, is 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]. Regarding the polarity, we decided to use anodal only in the left temporal area. This is because, in our pilot study, using cathodal stimulation over the left and anodal stimulation over the right ATL, we found no differences between active and sham stimulation. Finally, we decided to test two active conditions with reference electrodes of different sizes, in order to test whether stimulation of the contralateral, right, ATL plays a role in modulating false memories. A constant current intensity of 2 mA (current density of 0.06 mA/cm2) intensity was applied for approximately 10 minutes (according to the duration of the task – stimulation was ended when the task was completed). Cognitive tasks were initiated 5 minutes after the start of stimulation as it has been shown that 3 minutes of stimulation is the minimum duration of stimulation in order to induce significant after-effects changes in the cortical excitability [26]. Stimulation with 2 mA (for a single session) has been shown to be safe in healthy volunteers [27]. Experimental design After screening and consent, subjects were randomized to one of the three conditions of stimulation (bilateral, unilateral of sham stimulation). tDCS was then started and after 5 minutes of stimulation, the false memory task was initiated (referred in the PLoS ONE | www.plosone.org 2 March 2009 | Volume 4 | Issue 3 | e4959