Age-dependent effects of intranasal oxytocin administration were revealed by resting brain entropy (BEN)

Brain entropy (BEN) reflects the irregularity, disorderliness, and complexity of brain activity and has gained increased interest in recent years. The demonstrated sensitivity of BEN to caffeine and medicine suggests the existence of neurochemical effects of BEN. Oxytocin (OT), a neuropeptide associated with childbirth and lactation, affects both social behavior and brain activity. The purpose of this study was to examine whether OT affects BEN in young and old adults. A randomized, double-blind, placebo-controlled, two-factor (Age × OT) between-subjects design was used, and a total of seventy-five eligible healthy participants were included in the experiment. In the young adult group (YA), 23 participants received intranasal OT administration, while 18 received a placebo (PL) administration. In the older adult group (OA), 16 participants received intranasal OT administration, and 18 received PL administration. Using fMRI-based BEN mapping, we found the age-dependent effect of intranasal OT in the left temporal parietal junction (TPJ), where BEN increased in YA and BEN decreased in OA. A whole-brain functional connectivity (FC) analysis with the left TPJ as the seed and we found that FC between the left TPJ and right TPJ increased in both YA and OA. FC of left and right TPJ and plasma OT contribute to left TPJ BEN just found in YA with intranasal OT administration. These results indicate that BEN is sensitive to age-related effects of neurochemical signals and highlight plasma OT on the effects of intranasal OT in young adults.