According to the joint study that was run by Istanbul Medipol University and Maastricht University, “Yes”, with the frequency and task specific manner.
Recently published study in Scientific Reports highlights that in healthy individuals, by using transcranial alternating current stimulation (tACS) at individual theta frequencies calculated from the individuals’ own EEG data can affect their behavioral performance beyond the stimulation period itself.
The study, conducted by Tuba Aktürk and supervised by Prof. Dr. Bahar Güntekin and Prof. Dr. Alexander T. Sack, investigated the functional role of brain oscillations associated with human memory processing. Importantly, conceptual and technological approach used in the study made it possible to modulate neural oscillatory activity with measurable impact on both, neurophysiological assessments of neural oscillations as well as cognitive performances in various memory tasks.
Here, it was investigated if tACS, a method that enables rhythmic stimulation at a certain frequency (such 4 Hz), could be used to selectively interfere with the brain’s oscillatory activity. To alternate ongoing brain oscillations in the particular directions, tACS can give sinusoidal currents at the desired frequency. The stimulation applied by alternating current is thought to modulate the excitation times of neurons. It is suggested that the changed electric field exposure of synapses alters the biochemical processes that result in short-term synaptic plasticity. The cognitive processes that are predicated on the ongoing brain oscillations may be influenced by this external manipulation of the oscillations by tACS. If so, this method may have a significant impact on a variety of scientific and therapeutic applications since it offers the experimental opportunity to regulate and control brain oscillations through external intervention. The treatment promise for a wide range of diseases (osilopathies) whose deteriorating pattern is known to be manifested in brain oscillations cannot be overstated. The aim and impact of this study is clearly positioned within this framework.
The study’s findings revealed that unsurprisingly given the brain’s sophisticated and dynamic functioning, neuromodulation’s effects on behavior and brain oscillations are not as straightforward as predicted. Accordingly, it is shown that tACS may improve memory in healthy volunteers when delivered at a frequency slower than the individual theta frequencies of the individuals rather than at the individual theta peak frequency. However, in terms of neurophysiological effects this slowing down tACS approach did not cause changes in individual theta frequency as expected, instead, it caused the connectivity between the stimulated brain regions to be altered within a larger widely distributed frontoparietal network.
The study provides new fundamental insights into the functional roles of theta oscillatory frequency in the context of human memory processing, demonstrate the capability of tACS to modulate these neural oscillations as well as memory performance, causing tACS-induced cognitive enhancement that persist even after the tACS stimulation has been stopped. These results clearly hold great promise for therapeutic use in the relevant diseases.
Original Research: Aktürk, T., de Graaf, T.A., Güntekin, B., Hanoğlu, L., Sack, A.T. Enhancing memory capacity by experimentally slowing theta frequency oscillations using combined EEG-tACS. Sci Rep 12, 14199 (2022). https://doi.org/10.1038/s41598-022-18665-z
The coupling of gamma oscillation (~ 40+ Hz) amplitude to the phase of ongoing theta (~ 6 Hz) oscillations has been proposed to be directly relevant for memory performance. Current theories suggest that memory capacity scales with number of gamma cycles that can be fitted into the preferred phase of a theta cycle. Following this logic, transcranial alternating current stimulation (tACS) may be used to adjust theta cycles (increasing/decreasing theta frequency) to decrease or increase memory performance during stimulation. Here, we used individualized EEG-informed theta tACS to (1) experimentally “slow down” individual theta frequency (ITF), (2) evaluate cognitive after effects on a battery of memory and learning tasks, and (3) link the cognitive performance changes to tACS-induced effects on theta-band oscillations as measured by post EEG. We found frequency- and task-specific tACS after effects demonstrating a specific enhancement in memory capacity. This tACS-induced cognitive enhancement was specific to the visual memory task performed immediately after tACS offset, and specific to the ITF-1 Hz (slowing) stimulation condition and thus following a protocol specifically designed to slow down theta frequency to enhance memory capacity. Follow-up correlation analyses in this group linked the enhanced memory performance to increased left frontal-parietal theta-band connectivity. Interestingly, resting-state theta power immediately after tACS offset revealed a theta power increase not for the ITF-1 Hz group, but only for the ITF group where the tACS frequency was ‘optimal’ for entrainment. These results suggest that while individually calibrated tACS at peak frequency maximally modulates resting-state oscillatory power, tACS stimulation slightly below this optimal peak theta frequency is better suited to enhance memory capacity performance. Importantly, our results further suggest that such cognitive enhancement effects can last beyond the period of stimulation and are linked to increased network connectivity, opening the door towards more clinical and applied relevance of using tACS in cognitive rehabilitation and/or neurocognitive enhancement.”