The investigators have previously shown that non-invasive methods of brain stimulation such as the administration of transcranial infrared light to the prefrontal cortex (PFC) can result in improvements to cognition and emotion as well as brain oxygenation. This method is called transcranial photobiomodulation (tPBM).

The investigators hypothesize that tPBM can improve cognition and brain oxygenation in adults with attention deficit hyperactivity disorder (ADHD). The investigators will investigate the effects of repeated tPBM sessions on cognitive functioning in adults with ADHD. Specifically, the investigators hypothesize that participants that receive tPBM will show improvements in response control, sustained attention, and working memory, as well as improvements in prefrontal hemodynamics and a reduction in ADHD symptoms.

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.

Inclusion Criteria:

• English-speaking
• Adults of any sex
• Age range: 18-44 years
• Any ethnic/racial background
• Medical history of ADHD
• Participants may either be on a stable ADHD medication regimen (with no changes within two weeks prior to the study) or not taking medication.

Exclusion Criteria:

• Currently pregnancy
• Any sham or active photobiomodulation treatment within the past five weeks.

What data will be shared? Individual participant data that underlie the results reported in this study, after deidentification (text, tables, figures, and appendices).

A data dictionary, including a description of the variables and types of data, collected for each individual, will be provided. This data will include anonymized individual participant demographic information and all outcome variables (cognitive task data, spectroscopy data).

Beginning 9 months and ending 36 months following article publication.

The raw data will be made available by the researchers upon reasonable request by any qualified doctoral researcher (PhD, MD). They will be granted access by contacting the corresponding author/principal investigator (F. Gonzalez-Lima, utbrainproject@gmail.com).

It will be made available to qualified researchers whose proposed use of the data has been approved by an independent review committee (Institutional Review Board) identified for the purpose of individual participant data meta-analysis.

Proposals may be submitted up to 36 months following article publication. After 36 months, the data will be available in our University's shared network drive, but without investigator support other than deposited metadata.