Ketamine's rapid antidepressant and anxiolytic effects have captivated clinicians for years, but a quiet assumption has persisted: that the drug's neural mechanism is essentially the same regardless of which condition it treats. New EEG evidence challenges that assumption directly, suggesting ketamine may be doing genuinely different things in the brain depending on whether the patient carries a diagnosis of depression, PTSD, or OCD — a distinction with significant implications for dosing protocols and biomarker development.
In a counterbalanced, three-session crossover design, researchers administered intramuscular ketamine at 0.5 mg/kg and 1.0 mg/kg — alongside a fentanyl control — to participants with treatment-resistant MDD (n=25), TR-PTSD (n=22), and a preliminary TR-OCD cohort (n=7). Resting frontal EEG was recorded before and two hours post-infusion. The TR-PTSD group displayed clear dose- and frequency-dependent power shifts, with alpha-band activity showing the most pronounced changes at the lower 0.5 mg/kg dose. TR-MDD patients showed no equivalent pattern. TR-OCD differed qualitatively from both other groups. Crucially, the EEG bands that correlated most strongly with symptom improvement varied by diagnostic scale — meaning the neural signature of therapeutic response appears disorder-specific rather than universal.
This is an incremental but methodologically meaningful contribution to ketamine neuroscience. The crossover design with an active control addresses a genuine gap, as most ketamine EEG studies focus exclusively on depression. However, the TR-OCD cohort is too small (n=7) to draw firm conclusions, and the predominantly female PTSD sample limits generalizability. The finding that alpha oscillations dominate PTSD response at lower doses aligns with broader theories linking alpha suppression to trauma-related hypervigilance, but causal directionality remains unresolved. For clinicians, this raises the possibility that optimal ketamine dosing may eventually be stratified by diagnosis rather than administered uniformly — a meaningful shift if replicated in larger trials.