Effects of Transcranial Photobiomodulation in ADHD

This will be a double-blind, sham-controlled study to evaluate the neurobehavioral and PFC neurometabolic effects of repeated tPBM sessions in adults with ADHD. Adults with a history of medically-diagnosed ADHD will be recruited. Participants will be randomized to two arms: (1) active tPBM or (2) sham tPBM. All participants will complete three in-person sessions and one remote follow-up visit conducted online. Participant will receive three weekly sessions of tPBM targeting the PFC using a 1064 nm laser. Cognitive performance will be assessed using the continuous performance task and 2-back task at baseline and after the final tPBM session. The investigators predict that participants receiving active tPBM will show improvements in sustained attention, impulse control, and working memory. Functional near-infrared spectroscopy recordings, collected at baseline and post-treatment, will be used to evaluate changes in PFC hemodynamic response and network interactions (functional connectivity). The investigators predict that active tPBM will enhance the PFC hemodynamic response and strengthen network interactions across prefrontal subregions. Lastly, ADHD symptomatology will be assessed using the Adult ADHD Self-Report Scale at baseline, post-treatment, and at a four-week follow-up after tPBM. The investigators predict that participants receiving active tPBM will report progressive reductions in ADHD symptoms across time points.

Primary Outcome Measures

1. Performance on the Continuous Performance Task
   The Continuous Performance Task is a widely-used cognitive measure to evaluate sustained attention, vigilance, and response control. Participants respond to letters presented on a computer screen and inhibit their responses to the letter X. There is no score on a scale. An increase in Correct Rejections on CPT = better inhibition = better outcome of treatment.
2. Prefrontal oxygenation (functional near-infrared spectroscopy)
   Participants will wear a head-mounted functional near-infrared spectroscopy device that records changes in the concentrations of oxygenated hemoglobin potentially resulting from the treatment.
3. Scores on the Adult ADHD Self-Report Scale (ASRS) questionnaire
   The ASRS is an 18-question self-assessment tool created by the World Health Organization (WHO) which evaluates symptom severity of ADHD. Minimum score=18; maximum score=90; high score = more ADHD symptoms; lower score after treatment = better outcome.