Here is yet another of the increasing number of articles examining the effects of very weak electrical stimulation of our frontal scalp with surface electrodes. I've done a number of posts on this topic, the most recent citing concerns over do it yourself kits now available to anyone. Santarnecchi et al. address the frequency-specific effect of stimulation with the main physiological brain rhythms by comparing performance during four tACS (transcranial alternating current stimulation) conditions — 5 Hz (θ band), 10 Hz (α band), 20 Hz (β band), and 40 Hz (γ band) — and a placebo, sham stimulation. Their summary:
-Online prefrontal γ-tACS selectively accelerated logical reasoning.
-Effects were frequency and task specific
-This contrasts with views of gamma-band activity as a byproduct of neuronal activity
-Gamma-band activity plays a functional role in fluid-intelligence-based reasoning
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 (γ-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.
Left Middle Frontal Gyrus