The cerebral cortex can be divided into distinct areas based on the density of proteins involved in the serotonin system. Using positron emission tomography in healthy participants, the study quantified serotonin 1A receptors (n = 30), 5-HT2A receptors (n = 22), the serotonin-degrading enzyme monoamine oxidase A (n = 32), and the serotonin transporter (n = 24). Clustering analysis identified five optimal clusters of cortical regions defined by these molecular profiles. These clusters explained the effects of psychotropic drugs acting on serotonin, such as antidepressants and psychedelics, suggesting the method is useful for integrating multimodal imaging data in neuropharmacology and psychiatry.
Ketamine reduces sexual arousal in a sex-specific manner, which may explain why it is used recreationally in chemsex settings despite dampening sexual experience. In two placebo-controlled crossover studies with 67 healthy volunteers, subacute S-ketamine lowered arousal to heterosexual stimuli in women and to lesbian stimuli in men, while decreasing sexual aversion to gay stimuli in both sexes. Late racemic ketamine reduced arousal to heterosexual stimuli in men but increased aversion to gay stimuli in women. Ketamine also modulated calcarine gyrus activity differently in men and women. These sex-dependent effects on brain activity and sexual response may relate to ketamine's known sex-specific influences on stress resilience and psychosis-like symptoms.