Abstract
Introduction Response inhibition, as a hallmark of executive control, refers to the suppression of actions that are no longer required or that are inappropriate, which supports flexible and goal-directed behaviour in ever-changing environments. In this study, we intend to prove whether the boosting of theta activity by electrical stimulation in the prefrontal cortex (pre-SMA & IFC) would (1) increase theta power in prefrontal cortex; reduce alpha power in OPC; (2) reduce number of errors in a continuous performance task; (3) to see whether pre-SMA or IFG is the important structure for motor response inhibition and process monitoring. Methods The studies were approved by the Ethic Committee of the Faculty of Medicine Christian-Albrechts University Kiel. Stimulation Transcranial alternating current stimulation (tACS) was delivering by a battery driven stimulator (NeuroConn GmbH, Ilmenau, Germany) through conductive-rubber electrodes (9 cm 2 ). So far, 12 subjects participated in four different experimental studies and they received on separate days tACS at three frequencies (6 Hz over preSMA and over rIFG, 20 Hz (frequency of no interest) over rIFG and sham stimulation. The minimum period between sessions for a single subject was 7 days. To stimulate pre-SMA: 4 cm anterior to Cz ( matches Fz) and reference electrode over contralateral supraorbital area ; to stimulate IFG: crossing point between T8-Fz and AF8-Cz. Go/NoGo task each stimulus was displayed for 0.2 s and the inter-trial interval was 1.5 s. Participants were asked to respond to all digits except of “5” by pressing a button with the right index finger. Digits “1–4” and “6-9” are thus the Go stimuli and digit “5” the NoGo stimulus. Correct Go-trials were categorized as “hits”, correct No-Go-trials as “withholds”, and responses on No-Go as “false alarms”. Results Preliminary results with 14 subjects in each condition indicate that there’s a significant difference in reaction times between hits and false alarms (in all conditions), which is consistent with the literature. Regarding the differences between conditions, there are no significant statistical differences as of now, but this might be due to the small number of subjects in each condition. There seem to be slight trends for 6Hz pSMA compared to sham: Mean reaction times for hits and false alarms were highest for 6 Hz stimulation at the pSMA. Regarding the ratio of hits and false alarms (actual number divided by potential number), subjects had the highest ratio of hits in sham stimulation and the lowest ratio in 6 Hz stimulation of pSMA. The pattern for false alarms is similar: subjects had the lowest ratio of FAs in 6 Hz stimulation of pSMA with all other conditions appearing mostly equal. Conclusion Our behavioral results so far showed that tACS could have potential in modulating behavioral responses, however future studies could improve on this study by analyzing EEG-data as correlates of the behavioral data and having larger sample sizes.
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