A single low-dose infusion of ketamine in older military veterans with treatment-resistant depression temporarily increases the brain's neural complexity, measured by electroencephalogram (EEG) markers Lempel-Ziv complexity and multiscale entropy, within 30 minutes after infusion. These effects vary over time, with some complexity measures decreasing later. However, these changes in complexity were not linked to reductions in depressive symptoms after seven days. The findings suggest that ketamine produces broad, time-varying effects on brain dynamics beyond previously studied gamma oscillations, offering a potential non-linear marker of the drug's action.
Early trauma is linked to stronger glutamatergic synaptic strength in people with PTSD, measured via a novel in vivo marker called energy per cycle (EPC). In a sample of 34 adults (16 with PTSD, 18 healthy controls), higher early trauma correlated with higher EPC only in the PTSD group. Greater synaptic strength was associated with reduced behavioral inhibition, and EPC mediated stronger links between reward responsiveness and early trauma. These findings suggest that trauma-induced changes in synaptic plasticity may underlie psychiatric risk and point to potential targets for treatments like ketamine and psilocybin.