Effects of the Hallucinogen Psilocybin on Covert Orienting of Visual Attention in Humans

Psilocybin, a serotonergic hallucinogen, and the ecstasy-like drug MDE both slowed reaction times in a spatial attention task, while methamphetamine did not. Psilocybin caused especially slow responses to invalid cues at short intervals and a failure to inhibit responses to valid cues at long intervals for right visual field targets. These patterns resemble bilateral attention disengagement and a lateralized impairment of inhibition of return seen in acute psychotic states. The study used a double-blind design with 8 healthy volunteers per group. Limitations include small sample size, and the authors call for larger studies with other hallucinogens to explore links between visuospatial attention dysfunction and psychosis.

Study at a glance

Abstract

Hallucinogenic drug-induced states are considered as models for acute schizophrenic disorders (experimental psychoses). In a double-blind study with healthy volunteers we investigated the influence of the serotonergic hallucinogen psilocybin, the ecstasy-like drug 3,4-methylenedioxyethylamphetamine (MDE), the stimulant d- methamphetamine and placebo on covert orienting of spatial attention (n = 8 in each group). Reaction times were prolonged after ingestion of psilocybin > MDE, but not after d-methamphetamine. In addition, subjects on psilocybin exhibited particularly slow reaction times in invalid trials at short cue target intervals and failure of response inhibition in valid trials at long cue target intervals for right visual field targets. Despite some methodological limitations, these results are in line with both bilateral impairment of disengagement of attention and a lateralized impairment of inhibition of return (IOR) in productive psychotic states. Additional investigations with larger samples, different hallucinogenic substances (serotonergic agonists vs. NMDA antagonists) and different dose regimens are needed in order to further explore the suggested relationship between visuospatial attentional dysfunction and acute psychotic conditions.