Frequently Asked Questions

No statistically significant association was found between average daylight duration during treatment and rTMS outcomes in this study of treatment-resistant depression. The median average daylight duration was 704 minutes in responders, 701 minutes in remitters, and 718 minutes in nonresponders, and Mann-Whitney U testing showed no significant difference between responder and nonresponder groups or between remitter and nonresponder groups.

This study suggests that season-related daylight duration may not meaningfully change rTMS efficacy, so rTMS does not seem to be limited by time of year in this sample. The authors describe this as reassuring, but they also note that more research is needed before firm conclusions can be drawn.

The sample was highly treatment-resistant. All 151 patients had major depressive disorder with failure of 4 or more antidepressant medications from at least 2 different classes and had also had unsuccessful psychotherapy before completing rTMS.

The study used an FDA-approved Deep TMS H1-coil protocol targeting the left dorsolateral prefrontal cortex. Stimulation was delivered at 18 Hz in 2-second trains with 20 seconds between trains, for 55 trains total, which equals 1,980 pulses over 20 minutes, at 120% of motor threshold. Treatment was given daily for 6 weeks, followed by a taper of 3 sessions in week 7, 2 sessions in week 8, and 1 session in week 9.

Response was defined as a 50% or greater reduction in PHQ-9 or HDRS score, and remission was defined as a PHQ-9 score <5 or an HDRS score <7 during the treatment period. Patients with less than 50% score improvement were classified as nonresponders.

Among the 151 patients who completed treatment, 99 were classified as responders, 62 as remitters, and 52 as nonresponders. The study reports these groups to compare daylight duration across outcomes rather than to estimate treatment efficacy against a control group.

Daylight exposure was estimated as the average duration of daylight during each patient's rTMS treatment course. The investigators calculated this using open-access US Naval Observatory data for the dates of treatment and the location of the treatment center in Chambersburg, Pennsylvania.

The rationale was that rTMS effects may depend partly on the brain state present during stimulation, and daylight exposure could influence that state through mood-related and circadian pathways. The discussion notes that intrinsically photosensitive retinal ganglion cells project through pathways involving the suprachiasmatic nucleus and also directly to mood-related regions such as the medial amygdala and lateral habenula, which connect to circuits implicated in depression.

This was a single-center observational study of 151 patients who completed a full course of rTMS between August 2018 and August 2025. Because it was conducted at one site using one protocol and did not account for several possible confounders, the findings are best interpreted as a preliminary negative association rather than definitive proof that daylight has no effect.

• It was a single-site study using one rTMS protocol.
• Potentially important variables such as depression severity, concomitant medications, stress levels, and other environmental factors were not accounted for.
• Average daylight minutes may not capture the most relevant aspects of light exposure, such as timing of exposure or intensity.
• Only patients who completed the full course were analyzed; dropouts were excluded because they could not be categorized as responders, remitters, or nonresponders.