Anxiety disorders are the most common mental health diagnosis in the US; 19.1% of U.S. adults (23.4% for females and 14.3% for males). In addition, the Global Burden of Disease study (2010) found that anxiety disorders were the sixth leading cause of disability (years of life lived with disability). These debilitating disorders are characterized by excessive worry and fear about everyday situations, and physical symptoms including restlessness, being easily fatigued, difficulty concentrating, irritability, muscle tension, or sleep disturbance. Furthermore, anxiety is linked to other mental disorders including depression and substance abuse; is associated with cardiovascular disease risk factors and a higher rate of cardiovascular disease; and is related to premature mortality. These data have led to the investigation of a breadth of plausible treatments for anxiety, including medications and psychotherapy. However, likely due to the breadth of complex mechanisms involved in the pathophysiology of anxiety disorders and the unfavorable side effects of various medications, a considerable number of individuals do not have a satisfactory response to these treatments. This has led investigators to examine plausible novel interventions to alleviate anxiety and its symptoms.

Transcranial direct current stimulation (tDCS), a non-invasive central neuromodulatory technique that is inexpensive and safe, has been utilized to stimulate specific regions of the brain and has demonstrated promising results for alleviating anxiety and depression. (1) evidence supports the administration of anodal stimulation over the left dorsolateral prefrontal cortex (DLPFC) to excite neuronal activity and cathodal stimulation over the right DLPFC to inhibit activity (a bicephalic tDCS montage with 2 mA of stimulation at the left DLPFC) as the most effective tDCS treatment to alleviate anxiety in humans and (2) that "tDCS may be more effective when used in combination with drugs and cognitive behavioral therapies". However, results from studies that have examined the neurophysiological and behavioral effects of tDCS are not consistent. This is likely because the highest cortical current density may not have occurred directly under the target electrode, thus altering the effects of tDCS. High-density tDCS (HD-tDCS) is similar to conventional tDCS utilizing anode and cathode placement on the scalp to produce unidirectional current flow, however, to enhance precision and accuracy, HD-tDCS utilizes smaller electrodes and most often in a "4X1 ring" montage (center anode electrode surrounded by four return cathode electrodes). This HD-tDCS montage delivers a precise current to the intended target site and has been found to be well tolerated and safe for healthy humans. Furthermore, the utilization of HD-tDCS can facilitate the elucidation of mechanisms of action that can provide greater clarity regarding discrepant results in the literature and for considering future advancements in enhancing effective HD-tDCS implementation strategies. HD-tDCS stimulation increases the membrane potential by several millivolts without triggering an action potential.

Inclusion Criteria:

• Healthy adults
• aged 18 to 50
• consent and complete a Physical Activity Readiness Questionnaire (PAR-Q)
• be free from any neurological or psychiatric disorder
• not be taking any medication that could affect the central nervous system
• not have any contraindication for HD-tDCS (i.e. not having metal implanted in the head, pacemaker, medical bumps, seizures, lesions on the scalp or head ) or for bioelectrical impedance (i.e., electronic medical implant, such as a pacemaker or implantable cardioverter defibrillator, and limb amputation)
• not be regular users of tobacco products (cigarettes, cigars, chewing tobacco)
• not consume an average of more than ten alcoholic beverages per week

Exclusion Criteria:

• Individuals who do not meet the PAR-Q screening criteria for participation in moderate physical activity will be excluded from participating in this study
• women who are pregnant will be exclude from this study