Non-invasive brain stimulation has been shown to alter performance in both clinical and healthy populations on cognitive tasks. While the performance alterations have generally been shown to result in enhancement, mixed results remain in the literature. Much of the mixed results within the literature have been attributed to the use of different stimulation parameters, targeting of different brain areas, and using a variety of performance measures or assessing different constructs. However, non-invasive brain stimulation is a desirable method for enhancing Soldier performance given the ease of administration and minimal side effects as compared to other forms of performance enhancement (e.g., pharmaceuticals, caffeine). The objective of the current study is to evaluate the effects of non-invasive brain stimulation to the left dorsolateral prefrontal cortex in enhancing Soldier cognitive skills and performance on military tasks. A double blind within-subjects design will be used with healthy, rested Soldiers who will receive non-invasive brain stimulation and perform basic cognitive and operationally relevant tasks.

Inclusion Criteria:

1. Must be 18 (if active duty), 19 (if non-active duty) up to 40 years old.
2. Must have normal hearing, vision or corrected to normal vision, and cognitive function as determined by self-report and screening by study physician
3. Must have obtained at minimum 6 hours of sleep prior to data collection, as assessed by actigraphy data and self-report.
4. Must have refrained from consumption of caffeine, 16 hours, nicotine, 2 hours, and alcohol, 24 hours, prior to the study, assessed by self-report.

Exclusion Criteria:

1. The following medically-related exclusionary criteria will be used, as assessed and verified by the study physician:

   1. Haven taken any medications which induce drowsiness, such as over-the-counter antihistamines within 24 hours of participation in the study. Any self-medication will be assessed through self-report
   2. No current medical conditions or medications affecting cognitive function or attention.
   3. Any history of any attention deficit condition requiring medication.
   4. Any history of psychological/psychiatric disorder.
   5. Any history of seizures, migraines, or neurological disorders.
   6. History of a head injury involving loss of consciousness.
   7. Any metal implanted within the head (e.g., shrapnel, surgical clips) or any implanted devices (e.g., cardiac pacemaker, brain stimulator, hydrocephalic shunt).
   8. Skin condition on the scalp, such as psoriasis or eczema, or wounds on the head.
   9. Currently receiving hormonal therapy treatments, other than birth control or as determined by physicians.
   10. Potential for caffeine withdrawal symptoms that will impede cognitive testing.

2. Females with a known pregnancy, who test positively for pregnancy, or refuse the test will be excluded, given the lack of available research regarding the effects of tDCS during pregnancy. Known pregnancy will be assessed during screening, females without a known pregnancy will be requested to provide a urine sample during the screening procedures to ensure the absence of pregnancy.

Subjects and the research team will both be blind to the stimulation condition delivered at each test session. Access will be limited to the study physicians, investigators, and device programmers.