Brain Stimulation Can Impair Long-term Retention of Memory

Using a SAFMEDS task (Say All Fast a Minute Every Day Shuffled; designed to build fluency), this study investigates whether anodal transcranial electrical brain stimulation (tES) over the left dorsolateral prefrontal cortex, can modulate both learning ability and subsequent long-term memory retention. Using a within-subject design, participants (N=25) took part in 6 training sessions over consecutive days in which active or sham stimulation was administered randomly (3 of each). A computer based SAFMEDS task was used, containing flags unknown to the participants from countries around the world. Each training session consisted of the repetition of 8 pairs of flag/country names. The aim was to say aloud the name of the countries at least 60 times in one-minute blocks to reach a performance-based threshold. In two testing sessions, one day after the final training session and one week later, participants were tested on all 48 flags they had learnt. The participants were tested on both free recall and recognition. Results showed no difference in learning speed between active and sham stimulation for the training sessions. However, in the sham condition, recognition was significantly greater in the second testing session, compared to the active condition. Marginal significance was found for free recall for the sham condition compared to active, in the second testing session. These results show that for this particular task, anodal-tES was ineffective at improving learning ability and of detriment to performance in subsequent recognition and free recall tests, compared to the sham condition.