This project uses a hybrid trial design to evaluate two biomedical interventions targeting the gut-brain axis. One intervention is portable Transcutaneous Vagus Nerve Stimulator, tVNS, that is hypothesized to stimulate the autonomic nervous system, resulting in decreased inflammation and improved cognition. The second intervention is a probiotic supplement intended to replace gut bacteria that are associated with dysbiosis in persons with HIV and alcohol consumption.

Inclusion Criteria:

• Age 35-70 years
• English or Spanish speaking
• Alcohol users
• Cognitive impairment
• Current CD4>350

Exclusion Criteria:

• Diagnosed major psychiatric illness
• Consumption of over 300 drinks in the past 30 days
• Recent opioid use
• Lifetime history of medically-assisted alcohol detoxification
• Inpatient or intensive treatment for addictive behaviors in the past 12 months
• MRI contraindications
• Current antibiotic treatment
• Current probiotic use
• Physical impairment precluding motor response or lying still.

This is a 2x2 design in which subjects will be randomly assigned to one of 4 interventions groups: tVNS and probiotic (n=20); tVNS and placebo (n=20), sham stimulator and probiotic (n=20), and sham stimulator and placebo (n=20). We will use a computer-assisted stratified block randomization with block size of 4 to assign participants to the intervention. Study participants, investigators, staff, and physicians administering the probiotics or placebo will be unaware of specific group assignment. The stratified, blocked randomization and assignment of participants to the 4 intervention groups will be guided and monitored by Data Science Core.