This study evaluates the effect of frontal cortex transcranial direct current stimulation (tDCS) on the neural correlates of threat processing in healthy volunteers with a high level of trait anxiety. All participants received both active and sham tDCS and underwent a functional imaging scan whilst carrying out an attentional control task with fearful distractors.

There is a growing body of evidence suggesting that repeated administration of prefrontal transcranial direct current stimulation (tDCS) is a potential effective treatment for depression through restoring a left/right imbalance in frontal brain activity (Boggio et al., 2008; Loo et al., 2012) and improving top down control of anxiety responses.

An initial exploratory study was carried out in 2012 (Ironside et al 2015) to examine the effects of tDCS on emotional processing in healthy volunteers using a range of tasks and questionnaires. Using a dot probe task, which measures attention to happy or fearful faces, it was found that tDCS has the potential ability to reverse an attentional bias to fearful faces seen in the placebo group. This indicates that anxiety responses may be modified using tDCS and therefore this follow on study seeks to further explore the role of tDCS in trait anxiety and investigate the neural correlates of this with fMRI.

The present study uses behavioural and neuroimaging results to examine how tDCS affects emotional processing relevant to trait anxiety. A within-subjects design increases the power of the study, given limited resources to carry out extensive neuroimaging. Our working hypothesis is that tDCS may alter activity in cortical regions relevant to attentional control and anxiety.

The findings of this study will be used to determine parameters for future patient studies, involving participants with generalized anxiety disorder or major depression. The ultimate aim, explored through further studies, is to understand and improve how tDCS might be used in the treatment of these disorders.

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the study.
• Healthy female adults, right handed, aged 18-45 years.
• Participants will be asked to fill in a pre-screening online anxiety questionnaire (STAI-T) and will be invited to participate in the study if they score high within the normal range on trait anxiety.

Exclusion Criteria:

• Any current significant medical condition.
• Any current or past psychological disorder (for example depression or anorexia).
• Any family history of extreme mood fluctuations (such as elated mood states)
• Any current medications (except for contraceptive treatment) or herbal remedies such as St John's wort.
• Any current pregnancy or likelihood of becoming pregnant during the study.
• Any participation in any other psychological or medical experiment involving taking any kind of drugs, within the last 3 months.
• Previous participation in a brain stimulation study will be taken into account and advice will be sought from the secondary supervisor on whether they should be included, based on the type of stimulation received, the location of the stimulation and the number of sessions. If the secondary supervisor advises that the nature of the stimulation previously received could affect the results of this study, the participant will not be included.
• Participants should not be claustrophobic, have a heart pacemaker, mechanical heart valve, mechanical implant such as an aneurysm clip, hip replacement, or any other pieces of metal that have accidentally entered their body.
• Any other contraindication to magnetic resonance imaging or transcranial current stimulation.

Double blinding was carried out using a blinding code randomly assigned to each participant by a separate party. This code was entered into the transcranial direct current stimulation device by the investigator to deliver the stimulation. The investigator was not unblinded until initial analysis was complete.