Effects of psilocybin on functional connectivity measured with fNIRS: Insights from a single-subject pilot study

Psilocybin (17 mg) was given orally to a 31-year-old man, and functional near-infrared spectroscopy (fNIRS) measured brain hemodynamics and oxygenation over the frontal and occipital cortex before and 30 and 60 minutes after intake. Psilocybin altered functional connectivity in bilateral frontal, bilateral occipital, and right and left fronto-occipital regions. The subject's pulse rate also showed non-random variations possibly related to the substance. This first fNIRS pilot study demonstrates the technique can detect psilocybin-induced resting-state connectivity changes, though results are from a single participant and require replication with larger samples and improved setups.

Study at a glance

Abstract

The serotonergic hallucinogen psilocybin has characteristic effects on human brain activity and subjective experience. Previous functional magnetic resonance imaging (fMRI) studies showed alternations of functional connectivity (FC) under the influence of psilocybin in humans. No study, as yet, investigated psilocybin-induced changes in brain hemodynamics and oxygenation with functional near-infrared spectroscopy (fNIRS) optical neuroimaging. Our aim was to perform the first fNIRS single-subject pilot study in order to investigate the ability of fNIRS to detect changes induced by psychedelic substances. To this end, psilocybin (17 mg) was administered orally to a 31-year old man while resting-state changes in cerebral tissue hemodynamic and oxygenation were measured with fNIRS bilaterally over the frontal and occipital cortex. Measurements were performed before the intake of the substance as well as during its effective period (30 min and 60 min after intake). We observed psilocybin-induced changes in the bilateral frontal FC, bilateral occipital FC as well as right and left frontooccipital FC. In addition, the pulse rate of the subject showed non-random variations during the experiment, possibly related to psilocybin administration. This study demonstrates that fNIRS is able to detect psilocybin-induced changes in resting-state FC. The results of this initial single-subject pilot study are promising and warrants repetition with a larger number of subjects and an improved/extended fNIRS setup. We anticipate that fNIRS neuroimaging will play an important role in future studies investigating the neuronal/physiological effects of psychedelic substances in humans.