Applying Neuromodulation to Boost the Efficacy of Motivational Interviewing - The use of cannabis and alcohol is associated with myriad health consequences including motor vehicle crashes, myocardial infarction, and cancer risk. For example, alcohol accounts for nearly a third of head and neck cancers. Despite this, few adults with a substance use disorder (SUD) receive any form of treatment. When adults with an SUD do receive behavioral treatment, they typically receive only a single session. Given this, it is essential to make that one session count. There is a clear need for adjuncts to treatment for people who have an SUD. One potential way to boost the efficacy of treatment is non-invasive brain stimulation such as transcranial alternating current stimulation (tACS), which involves administering small electrical currents through scalp electrodes. tACS delivers sinusoidal currents similar to those produced by intrinsic neuronal oscillations – that is, brain rhythms. Because of this, tACS can be used to enhance a given brain rhythm. This is important because brain rhythms mediate a broad range of brain functions, including processing of sensory stimuli, attention, memory and the generation of motor output, as well as to contribute to activity-induced synaptic plasticity. They also play a causal role in linking distributed brain regions into functional networks. Testing the causal effects of neuronal oscillations in SUD using tACS could mark a significant step forward for SUD research and treatment. Our pilot data suggest that within motivational interviewing (MI) treatment sessions, brain rhythms in the beta frequency band (15-25 Hz) are stronger during client statements supporting behavior change (“change talk”) than during client statements supporting the status quo (“sustain talk”). A large body of research in MI indicates that the quantity of the client’s change and sustain talk during their intervention session is related to their SUD outcomes. Our data suggest that using tACS to enhance beta band brain rhythms may boost the effects of client change talk and reduce those of client sustain talk. Therefore, in the UG3 phase we propose to test the effects of an MI and tACS intervention in a randomized trial to modulate change talk and oscillatory brain activity. In the UH3 phase, we will test the effects of the MI and tACS intervention on brain functional networks and substance use outcomes. If successful, this UG3-UH3 phased innovation study will provide a new and accessible means of boosting the efficacy of motivational interviewing, improving outcomes for people with a substance use disorder.