A subanesthetic dose of ketamine increases gamma oscillations in the prefrontal cortex and hippocampus, brain areas linked to its rapid antidepressant effects, and produces a 3 Hz oscillation in the posteromedial cortex that may underlie its dissociative effects. By adding propofol, which blocks NMDA-mediated disinhibition and shares HCN1 inhibition with ketamine, the study distinguished brain dynamics caused by NMDA-mediated disinhibition from those caused by HCN1 inhibition. The results suggest ketamine engages distinct neural circuits in frequency-dependent patterns to produce antidepressant and dissociative effects, potentially guiding development of new depression therapies with fewer side effects.
Convergent neurons—those that receive input from multiple sources but do not integrate that information—more readily exhibit properties of consciousness than integrative neurons, contrary to the predictions of integrated information theory. In nonhuman primates under propofol anesthesia, convergent neurons showed greater neural complexity and noise correlation, and were more impacted during loss of consciousness. Neural ignition, the coactivation of primary somatosensory and ventral premotor cortex on the same trial, was more frequent in conscious states, supporting the global neuronal workspace theory. The findings directly contrast two major theories of consciousness within a single dataset.