Bipolar Transcranial Alternating Current Stimulation (tACS)

The score was calculated by summing the severity score of items that were rated by the participant as related to stimulation on the Stimulation Side Effects Questionnaire. There was a total of 14 symptoms listed on the questionnaire. Participants rated each item rated on a scale of 0-4, with 0 meaning no relation and 4 meaning definitely related. The total possible range of the questionnaire was 0-56.

Results reflect the number of participants who withdrew from the trial during or after a stimulation session with either the tACS or the sham stimulation treatment.

The Go/NoGo task was a cognitive task, where participants were shown "go" stimuli (i.e., go trials) and "no-go" stimuli and responded by pressing a button when seeing "go" stimuli and not responding when seeing the "no-go" stimuli. Accuracy was measured by calculating D' (D prime), which provided a measure of perceptual sensitivity to the differing stimuli. Larger values of D' indicated greater discernability (i.e., accuracy) between the Go and NoGo trials. D-prime, also called the sensitivity index represents how well someone can detect a signal amidst background noise. At its core, D-prime is the standardized difference between the means of the Signal Present and Signal Absent distributions, which can be calculated by taking the difference between the Z-score of the False Alarm Rate and the Z-scores of the Hit Rate. A D-prime of 0 means no sensitivity. Negative D-prime values are rare and may indicate errors or reversed interpretations of hits and false alarms.

The Go/NoGo task was a cognitive task, where participants were shown "go" stimuli (i.e., go trials) and "no-go" stimuli and responded by pressing a button when seeing "go" stimuli and not responding when seeing the "no-go" stimuli. Response bias was measured using beta, such that more negative beta values indicated a stronger tendency to respond to all stimuli, regardless of "go" or "no-go" status. Response bias is indexed by taking the average between the Z-score of the False Alarm Rate and the Z-scores of the Hit Rate. A higher response bias indicates that the participant is more likely to respond "signal absent" (favors avoiding false alarms but increases misses). A response bias of 0 means the individual equally weighs the costs of misses and false alarms. A more negative response bias indicated that the participant is more likely to respond "signal present" (favors hits but increases false alarms).

Participants' reaction time to responding to the "Go" signal during the Go/NoGo task was measured.

Theta-gamma phase-amplitude coupling (PAC) is a neural phenomenon observed in the brain, where the phase of slower theta oscillations modulates the amplitude of faster gamma oscillations. This type of coupling is thought to play a critical role in various cognitive control. For the trial, higher PAC values indicated higher levels of coupling or connection between the two frequencies (i.e., increased cognitive control).

After completing the Emotion Go-NoGo task, participants will complete another cognitive control task (i.e., Emotional Flanker Task) with gray-scaled unpleasant, pleasant, and neural images from the International Affective Picture System. Participants are tasked with indicating which valance is presented in certain images while ignoring other images. Accuracy is defined as the percentage of trials that the participant correctly reports the valance of the target image. The total number of correct trials will be divided by the total number of trials to obtain an accuracy score. Average accuracy scores per condition and total will be calculated.

Reaction time will also be collected during the Emotional Flanker Task. Reaction time is defined as the length of time it takes the participant to respond after the onset of the stimuli. Average reaction times per condition and total will be calculated.

EEG will also be collected during the Emotional Flanker Task. Phase-amplitude coupling will be calculated and defined as the coupling between the amplitude of high frequency oscillations (e.g., gamma) and low frequency phase (e.g., theta). Average coupling scores per condition and total will be calculated.