Modulating Default Mode Network Function: A Transcranial Direct Current Stimulation (TDCS) Pilot Study

The primary purpose of this research is to gather scientific information about how different people's brains work when they look at different types of pictures. This will help to improve the investigators' understanding of the way the brain works for people who are depressed or anxious, and this knowledge could help lead to better diagnosis and treatment.

In this study the investigators are examining the effects of weak electrical stimulation on brain activity as measured by functional magnetic resonance imaging (fMRI). MRI is a widely used method to obtain high resolution brain pictures that are routinely used for diagnostic and clinical purposes. The electrical stimulation is applied on the scalp with a non-FDA approved method called tDCS (transcranial Direct Current Stimulation), typically equivalent to what a 6V battery would produce (and up to no more than 15V). To compare, an AA battery delivers current at 1.5 volt. While almost unnoticeable to the participants, these currents can still temporarily affect brain activity without causing adverse effects. This stimulation would be applied while the participants are in the MRI scanner so that the brain activity can be measured. The participants will have the opportunity to have a test session with the stimulation outside the scanner to get familiar with it.

Eligibility Criteria:
Inclusion Criteria:

1. Between 18-30years old
2. Score \> 10 on the QIDS or \> 60 on the PROMIS-A
3. We will use a flexible extreme groups recruitment strategy to ensure an adequate distribution of ESC scores. We will ensure that at least 62% of the sample will be composed of those scoring .5 SD above or below the mean, as measured by the NEO-PI-R. This value corresponds to the expected values assuming a normal distribution of the trait.
4. Normal or corrected to normal vision with contact lenses
5. Able to provide informed consent in English
6. Right-handed (Annett criteria)

Exclusion Criteria:

1. Have a history of head trauma with loss of consciousness.
2. Have a systemic medical illness that may impact fMRI measures of cerebral blood flow.
3. Meet standard exclusion criteria for fMRI scanning (e.g. claustrophobia, cardiac pacemakers, neural pacemakers, surgically implanted metal devices, cochlear implants, metal braces, or other MRI non-safe metal objects in the body).
4. Are pregnant (self report and tested for as part of any scan by the scanning center and not this protocol)
5. Not native English speaking or not fluent
6. Premorbid NAART IQ estimate\<85;
7. Visual disturbance (worse than 20/40 Snellen visual acuity) that is not corrected
8. If have visual disturbance, only access to correction with glasses (i.e., no access to contact lenses).
9. Left/mixed handedness (Annett criteria), to ensure a uniform hemispheric dominance for interpretation of neuroimaging data
10. Active suicidal ideation in need of immediate treatment
11. Scoring below the cutoffs on both the QIDS and the PROMIS-A
12. History of alcohol/substance use disorder (including nicotine) and/or illicit substance use (except cannabis) over the last 3 months, determined by the MINI. Lifetime/present cannabis use (non-disordered levels) will be allowed, given its common usage in individuals in this age range.
13. Current or past psychotic-spectrum disorder
14. History of seizures