The human brain's activity constantly reorganizes across space and time, and decomposing whole-brain recordings into harmonic modes reveals gradient-like patterns linked to different functions. Using the HADES framework, researchers analyzed brain activity in healthy participants after taking the serotonergic psychedelic DMT. They found significant decreases in contributions across most low-frequency harmonic modes during the DMT state. Specifically, the second functional harmonic, which represents the uni- to transmodal functional hierarchy, decreased, supporting the hypothesis that psychedelics alter this hierarchy. Dynamic measures of fractional occupancy, lifetime, and latent space precisely described the changes in the brain's spacetime hierarchical organization during the psychedelic state.
Daily injections of phencyclidine (PCP) at 3.0 mg/kg or ketamine at 0.8 mg/kg in two macaque monkeys produced robust reductions in accuracy and increases in reaction time during high cognitive-demanding tasks. Saccades, smooth pursuit, and fixation stability were significantly impaired; involuntary microsaccades during fixation increased in amplitude and were biased toward the lower visual field. Pupillary response during cognitive tasks was reduced, and sensitivity to auditory cues increased as shown by auditory evoked potentials. A machine-learning classifier identified altered states induced by different drugs with 93% accuracy, and 90% accuracy when data from one monkey trained and tested the other, demonstrating data transferability across individuals.