Frequency-dependent enhancement of fluid intelligence induced by transcranial oscillatory potentials.
Everyday problem solving requires the ability to go beyond experience by efficiently encoding and manipulating new information, i.e., fluid intelligence (Gf) . Performance in tasks involving Gf, such as logical and abstract reasoning, has been shown to rely on distributed neural networks, with a crucial role played by prefrontal regions . Synchronization of neuronal activity in the gamma band is a ubiquitous phenomenon within the brain; however, no evidence of its causal involvement in cognition exists to date . Here, we show an enhancement of Gf ability in a cognitive task induced by exogenous rhythmic stimulation within the gamma band. Imperceptible alternating current  delivered through the scalp over the left middle frontal gyrus resulted in a frequency-specific shortening of the time required to find the correct solution in a visuospatial abstract reasoning task classically employed to measure Gf abilities (i.e., Raven's matrices) . Crucially, gamma-band stimulation (gamma-tACS) selectively enhanced performance only on more complex trials involving conditional/logical reasoning. The present finding supports a direct involvement of gamma oscillatory activity in the mechanisms underlying higher-order human cognition.