Using mild non-invasive brain stimulation for identifying and targeting brain-based changes in anxiety.

This study will take place across 3 sessions, with the 2nd and 3rd session following a cross-over design. An interval of at least 72 hours will be mandatory between the two transcranial alternating current stimulation (tACS) sessions to ensure no carry-over effects of stimulation. All three sessions will be conducted within 3 months’ time from the first session. Session 1 outline (duration: approximately ~1.5 hours) Baseline characterization of participants. Including: Relevant demographic and health-related information: i.e. age, gender, education, current diagnoses and any medication or treatment they are currently receiving. Cognition: this will involve a cognitive battery of tests that will include: Forward and Backward Digit Span test, Trail Making Test (TMT), Symbol Digit Modalities Test (SDMT), Brief Visuospatial Memory Test Revised (BVMT-R), Rey Auditory Verbal Learning Test (RAVLT) and F-A-S test. Measure of clinical anxiety severity (Beck Anxiety Inventory). Measure of depression severity (Beck Depression Inventory); given the high co-morbidity between depression and anxiety. The cognitive battery and measures of clinical anxiety and depression severity are to be used as a baseline characterization of participants. This will be followed by randomized and counterbalanced sequence of two sessions of tACS conducted at least 72 hours apart, each approximately (1-1.5 hours in duration) with details as follows: 1) 2 x 10 minutes blocks of tACS set at an individualized intensity applied bilaterally to the left and right dorsolateral prefrontal cortex (DLPFC) during an attentional control task (the flanker task) with resting EEG, state anxiety levels (measured with STAI-6) and alertness/arousal (measured on a 10-point visual analogue scale) measured pre- and post- stimulation. 2) 2 x 10 minutes blocks of sham (placebo) tACS with 30 seconds 'fade in' to a participant's individualized intensity followed by an immediate 30 seconds 'fade out' (i.e. zero stimulation) applied bilaterally to the left and right DLPFC during an attentional control task (the flanker task) with resting EEG, state anxiety levels (measured with STAI-6) and alertness/arousal (measured on a 10-point visual analogue scale) measured pre- and post- stimulation. During the first of these two tACS sessions, task-related EEG will be measured during two attentional control tasks: the Classical Stroop Task and the Emotionally-Modified Stroop task. Stroop task type order will be randomized and counterbalanced. Comparing the task-related EEG and Stroop reaction time results is a secondary aim of the study, examining differences in emotional and non-emotional attentional control. Note regarding individualization: intensity i.e. the amount of mA will be determined for each individual by the method of perceptual thresholding. This is where the intensity i.e. mA is increased until the participant sees phosphenes (flashing lights), then the amount of mA is set just below this level. This is a common method used in tACS studies. Stimulation intensity will not exceed 2.0mA. Data collection including attentional control tasks and resting and task-related EEG and tACS administration is to be conducted by Jessica Michael (PhD candidate) at the Epworth Centre for Innovation in Mental Health (ECIMH). Baseline cognition may be conducted on-site at ECIMH or remotely via teleconferencing software. Please note that as of September 2022 (post-enrolment) there has been a change of site to the Monash Alfred Psychiatry Research Centre, as the ECIMH closed down.