Molecular brain imaging of psychedelic action.

Molecular brain imaging techniques such as PET and SPECT have been used since the 1980s to study psychostimulants, and more recently to investigate psychedelics. Most published research involves SPECT studies of cerebral blood flow and PET studies of metabolism and neuroreceptors, particularly the 5-HT2A receptor, which is primarily responsible for the effects of classical psychedelics. Some evidence documents interactions at dopamine D2/3 receptors in the striatum, but many other potential molecular targets remain unexplored. The growing therapeutic use of psychedelics for neurological and psychiatric disorders highlights the need for broader, systematic investigation of their effects on brain function.

Study at a glance

Abstract

Molecular brain imaging by positron emission tomography (PET) and single photon emission computer-tomography (SPECT) entails the mapping of the cerebral distribution of radiopharmaceuticals that track physiological processes such as blood perfusion and glucose metabolism, or the abundance in brain of specific molecular targets such as neuroreceptors. PET and SPECT emerged as useful in vivo research technologies in the 1980s, finding early application in the study of psychostimulant drugs. The past decade has seen growing use of molecular imaging methods in the study of psychedelic action, although the published literature remains comparatively small. The preponderance of publications cited in this review are SPECT studies of cerebral perfusion and PET studies of metabolism and neuroreceptors, the latter mainly focusing on the 5-hydroxytryptamine (serotonin) 5-HT2A receptors, which are largely responsible for the psychedelic action of classical psychedelic substances. There is some documentation of interactions of psychedelics at dopamine D2/3receptors in the striatum, but many other plausible molecular targets of psychedelic action await investigation by molecular brain imaging. The emerging role of psychedelics as treatments for neurological and psychiatric disorders calls for a broader and systematic investigation of their effects on brain function.