IS 47. Frequency-dependent boosting of fluid intelligence during weak prefrontal alternate current stimulation

Background Modulation of ongoing brain activity through transcranial direct and alternate current stimulation have been already demonstrated, using both steady state cortical excitability and task-related motor performances as final outcome indexes. The opportunity to modulate, i.e. enhance or inhibit, higher level cognitive abilities in the same way is an intriguing scenario, especially for a cognitive rehabilitation perspective, although no evidences have been provided so far. Objective To originally investigate the possibility to modulate abstract reasoning and logical abilities through transcranial alternate current stimulation (tACS), 15 healthy subjects, naive to tACS, underwent a Raven progressive matrices-alike cognitive task, composed by 60 randomized stimuli divided into 4 increasing difficulty levels (namely “1”, “2”, “ 3 Relations ” and “ Logic ” matrices). Five parallel version of the task have been created using SANDIA software and used during 5 randomized separate tACS sessions (5/10/20/40 Hz/sham at 1 mA stimulation intensity), carried out using a bipolar montage (active electrode on left middle frontal gyrus, vertex reference). As a control task, additional reaction times (RTs) were measured throughout the experimental sessions, by using a low-cognitive load odd/even pc-based task. Methods The relationship between performance and the predictors of interest, i.e. tACS (sham/5/10/20/40 Hz) and kind of test (LOGIC and 1/2/3 RELATIONS) was investigated through gamma (for reaction time) and logistic (for accuracy) regressions. Results A main effect of Task on both accuracy ( X 2  = 3668.5, p X 2  = 424.6, p X 2  = 13.6, p X 2  = 0.3, n.s). Consistently, the presence of interaction between tACS and task for RTs (40 Hz; X 2  = 97.7, p X 2  = 125.6, p Conclusions results originally show a possible online boosting of higher order cognitive abilities using tACS. The frequency-dependent gamma-band tACS effect on RTs offers an interesting hypothesis about a cognitive flexibility improvement during high loading tasks (3 relations and logic), possibly induced by an entrainment of gamma stimulation. Such an entrainment might cause an increase of gamma bursts occurrence typically observed during problem solving.