Applying Neuromodulation to Boost the Efficacy of Motivational Interviewing

Motivational interviewing is a widely used counseling approach for substance usedisorders, including cannabis use disorder. A central proposed mechanism of motivationalinterviewing is that clients resolve ambivalence by hearing themselves express reasonsfor change and reasons for maintaining current behavior. Prior empirical andmeta‐analytic research has linked these within‐session speech patterns with subsequentsubstance use outcomes.This proof‐of‐concept randomized, double‐blind, sham‐controlled trial tests whethertranscranial alternating current stimulation (tACS) can modulate this mechanism during amotivational interviewing session for adults with cannabis use disorder. tACS is anoninvasive form of brain stimulation that delivers weak sinusoidal electrical currentthrough scalp electrodes. In this study, stimulation is designed to target beta‐bandactivity in left inferior temporal cortex, a region and frequency range implicated inspeech acts and commitment‐related language. Pilot work suggests that beta‐band activitymay be stronger during statements favoring behavior change than during statementsfavoring continued substance use, and that tACS during motivational interviewing isfeasible.Participants are assigned to motivational interviewing with active tACS or motivationalinterviewing with sham stimulation. Both groups receive a single motivationalinterviewing session focused on cannabis‐use ambivalence while the stimulation device andscalp electrodes are in place. The active condition includes approximately 30 minutes of20‐Hz beta‐frequency stimulation focused on left inferior temporal cortex at 2.0 mA totalcombined current across electrodes. The sham condition uses the same setup with brieframping procedures to emulate the sensations of active stimulation but without activestimulation during the intervention period.The study evaluates whether active tACS, compared with sham stimulation, affects clientspeech during the motivational interviewing session, post‐session brain activity, andcannabis use during the month after the session. Session audio is analyzed to quantifyspeech that favors change and speech that favors continued cannabis use. Neuroimagingmeasures include magnetoencephalography (MEG) and magnetic resonance imaging (MRI) afterthe intervention session. Post‐stimulation resting MEG is co‐registered to structural MRIto estimate, with particular interest in beta‐band activity in left temporal cortex inMEG. Near‐term cannabis use is assessed with daily self‐report check‐ins and a follow‐upassessment approximately one month after baseline.The trial is intended to provide mechanistic evidence about whether noninvasiveneuromodulation can alter a candidate process of behavior change during psychotherapy.The study is not designed to provide ongoing substance use disorder treatment, but totest whether pairing tACS with a brief motivational interviewing session changes speech,brain activity, and short‐term cannabis‐use outcomes relative to a sham‐stimulationcomparison.