transcranial brain stimulation

Summary: tACS & Fluid Intelligence

Researchers have used electrical stimulation to study the brain for decades. In this post, we will review one of the most interesting studies on tACS.

The research question: Does left-parietal theta tACS improve performance on fluid intelligence tests and what is the neurophysiological basis?


Fluid intelligence regards our ability of problem solving and abstract thinking, thus significantly affects our quality of life. In the present study, scientists stimulated a specific brain region associated with fluid intelligence, the parietal cortex, and observed an improved performance of participants on a relative behavioral task, compared to non-stimulated conditions. Furthermore, using functional brain imaging technics (fMRI), they showed that this improvement was not due to an increased activity of the brain areas involved in the task, but rather due to the decreased activity of task-irrelevant brain regions. These experimental findings support the neural efficiency hypothesis, which posits that intelligence is determined by the efficient use of brain resources and thus predicts that intelligence performance is associated with reduced activation of brain areas that are not central for intelligence.

Study Design

Participants received a sham (placebo) or verum (active) stimulation and then performed two intelligence tasks under the fMRI scanner. The matrices task, based on the Raven’s progressive matrices (RPM test), consisted of 50 items presented in a fixed sequence of increasing difficulty. Each item was presented with four response alternatives. The paper folding task (PFT) consisted of 20 items, presented in a fixed quasi-randomized sequence. Participants had to judge which of the four presented figures on the right side corresponded to that one on the left side after variable steps of folding and cutting. Dependent variables were performance in the two fluid intelligence tasks as well as BOLD responses in fMRI.

tACS Settings

tACS was administered with the following parameters:

  • Duration- 15 min (duration of stimulation in the sham condition was 60sec)
  • mA- 1500 μA.
  • Hz- 5 Hz
  • Electrode Position- “Target electrode was placed over the left parietal location (P3)”
  • Electrode Position- “return electrode was placed on Cz”


The behavioral tests showed that left parietal theta transcranial alternating current stimulation (tACS) significantly improves performance in the difficult questions of the Raven’s progressive matrices test, but not on the paper folding test.

The fMRI data indicated that tACS lead in a decreased activation of task-irrelevant brain regions, providing experimental evidence for the neural efficiency hypothesis of intelligence.

Relevant Quotes

  • Altogether, our study suggests that the main mechanism underlying theta tACS-stimulation effects can be seen in brain activation decreases of task-irrelevant brain regions rather than increases in task-relevant regions, which is in line with the neural efficiency hypothesis.”
    • Notes- The study provides experimental evidence for the neural efficiency hypothesis.
  • “This study replicates previous research showing that left parietal theta tACS leads to increased task-specific reasoning performance”
    • Notes- Like previous research, this study confirms tACS can improve a person’s reasoning abilities & fluid intelligence. 
  • “It should be acknowledged, however, that the current findings can only be interpreted in terms of a transient increase in the performance on a specific fluid intelligence task, which can be seen as an enhancement of a subfactor (namely fluid reasoning) rather than a general “intelligence boost” 
    • Notes- This quote clarifies that the improvement seen upon tACS might be short term. Using tACS while performing a specific task will boost cognitive abilities. We are unsure if tACS can create changes to one’s general intelligence.


Neubauer, A. C., Wammerl, M., Benedek, M., Jauk, E., & Jaušovec, N. (2017). The influence of transcranial alternating current stimulation (tACS) on fluid intelligence: An fMRI study. Personality and individual differences, 118, 50-55.

Links To Original




Sign UP for alerts

Click below and receive an email when the Supra Cortex is released for rental or purchase.

Sign Up For Alerts


Improved performance in and out of the cage