According to the authors of the study, while “serotonergic psychedelic psilocybin acutely induces changes in emotional states,” it “remains unresolved whether psilocybin acutely modulates amygdala reactivity to emotions, a brain region critically involved in emotion processing.” (The amygdala “is a brain region critically involved in processing emotions…particularly important for detecting the salience and social relevance of threat-related information in the environment,” the authors said.

) In addition to analyzing the 26 individuals’ responses to the various facial expressions, the study also “evaluated whether plasma psilocin levels (PPL) and subjective drug intensity (SDI) during psilocybin are related to amygdala responses to the emotional faces.” “We found that [the] amygdala response to angry faces was significantly reduced during exposure to psilocybin as compared to baseline, whereas no significant changes in amygdala responses to fearful or neutral faces were observed,” the researchers wrote.

“We further found that the amygdala response to fearful faces was significantly negatively associated with SDI, whereas no significant association with PPL was observed. Our findings indicate that psilocybin attenuates amygdala reactivity to angry faces and that a more intense subjective psilocybin response (SDI) is associated with attenuated amygdala reactivity to fearful faces, in accordance with previously reported results. Future studies should investigate whether exposure to psilocybin acutely changes emotion processing in individuals with depression and whether such changes are related to therapeutic outcomes.

” The authors noted that, “At baseline, we observed a pronounced response of the amygdala to each of the emotional faces contrasted with geometric shapes.” “The amygdala response to angry faces was significantly decreased during psilocybin intervention compared to baseline. The amygdala response to fearful faces was numerically decreased during psilocybin intervention, but this effect was not statistically significant (mean difference. Amygdala response to neutral faces was only slightly numerically increased during psilocybin intervention and was not statistically significant[ly] different,” they said.

The researchers said that the “amygdala response to angry faces was significantly reduced during acute effects of psilocybin compared to baseline,” but there “were no significant changes in the amygdala responses to fearful or neutral faces, although amygdala response to fearful faces was numerically reduced compared to baseline.”  “We observed a significant negative association between SDI and amygdala response to fearful faces, meaning that a more intense psychedelic experience is associated with greater reduction in fear processing.

Our findings show that amygdala response to emotional faces changes during acute effects of psilocybin, which is consistent with previous self-reports describing substantial changes in emotional orientation during a psilocybin experience,” they said. “As hypothesised, we find that the amygdala response to angry faces was significantly reduced during psilocybin intervention, but, inconsistent with our hypothesis, we find that the amygdala response to fear was not statistically significantly affected.

However, our results showed that the mean amygdala response to fearful faces was numerically reduced, which was not the case for the response to neutral faces, which remained more or less unchanged from baseline to psilocybin. Our result partially aligns with a previous fMRI study investigating amygdala responses to negative and neutral scenes during psilocybin intervention. This study found that amygdala responses to both negative and neutral scenes (e.g., neutral pictures of humans, animals or daily activities contrasted to shapes) during psilocybin intervention were significantly lower compared to placebo.

” Despite the findings, the researchers did note that additional research is necessary. “Although participants were blind to the receipt of psilocybin in the current study, we suggest that future studies include a placebo or low-dose group to better control effects related to potentially confounding factors, e.g., unblinding or expectancy,” they said. They detailed other limitations to their study, as well. “Due to practical constraints beyond our control, participants were subjected to scanning using one of two 3 T Siemens Prisma MRI scanners, with each individual’s scans being completed on a single scanner,” the authors said.

“While this approach ensured consistency, it also introduced potential heterogeneity in our data stemming from differences between scanners. To mitigate this, we incorporated the MRI scanner type as a covariate in all our analyses. Furthermore, we assessed the tSNR in the amygdala and evaluated the differences between scanner environments, which showed comparable tSNR values. Additionally, considering the susceptibility of multiband EPI sequences to head movement, we evaluated the effects of scanner on framewise displacement, which also showed a non-significant difference between scanner environments.

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