Researchers identify a time-specific brain signal tied to ketamine’s antidepressant benefit in older adults

# What the study did Researchers at Texas A&M's Experimental Psychopharmacology of Mood and Anxiety Disorders Lab examined how brain communication changes after a single intravenous ketamine infusion in U.S. veterans older than 55. Their goal was to link time-specific changes in brain activity to clinical antidepressant effects and to look for measurable brain signals that might explain differing patient responses.

# Who was studied

# How brain activity was measured

# Main findings The EEG showed distinct patterns of network-level activity at each time point. The critical result was that larger increases in one higher-order information-sharing measure at 24 hours correlated with greater reduction in depressive symptoms measured on day seven. In short, the way information across the brain reorganized a day after treatment predicted subsequent clinical benefit.

# How the authors interpret the signal The researchers frame ketamine's action as briefly releasing glutamate and transiently increasing connectivity across brain circuits. The degree and pattern of how that increased connectivity becomes organized, rather than only the immediate magnitude of change, may determine clinical response. The 24-hour network pattern may reflect a form of brain flexibility that supports symptom improvement over the following week.

# Why methods matter here Higher-order interaction analysis examines multichannel relationships at once, so it can capture network-level reorganization that pairwise measures miss. Because ketamine's pharmacological exposure is brief but its antidepressant effects can last days, studying how distributed brain activity evolves over hours and days provides different mechanistic insight than single-time-point measures.

# Potential applications and next steps The 24-hour EEG pattern could serve as a candidate biomarker for ketamine response in older adults. That would help researchers test alternative ways to provoke similar therapeutic reorganization or refine treatment timing. The study replicates and extends prior higher-order interaction work done in healthy volunteers, but further research will be required to validate the signal in larger and more diverse samples and to connect it to clinical decision-making.

# Bottom line In this older adult veteran sample, ketamine produced evolving, time-specific changes in brain network communication. A particular increase in multichannel information sharing at 24 hours predicted symptom improvement at day seven, suggesting that transient reorganization of brain networks may be an important component of ketamine's antidepressant effect and a potential biomarker to study treatment response.