Increased Activation of Indirect Semantic Associations under Psilocybin

This early double-blind, placebo-controlled study (1995, n=8) suggests that psilocybin increased indirect semantic priming. The authors add, however, that the setting alone led to a similar effect.

Abstract

“Hypothesized that psilocybin might exert a defocusing effect on semantic networks (i.e., decrease the signal-to-noise ratio), which should lead to an increased indirect semantic priming effect. A double-blind, placebo-controlled study was conducted on the effects of psilocybin on semantic and indirect semantic priming with 8 normal males (mean age 39.4 yrs). The finding that psilocybin increases indirect semantic priming in normal Ss adds to the general understanding of the effects of hallucinogenic agents on cognitive functions. Data indicate that indirect semantic priming is a highly sensitive measure that appears to respond not only to pharmacologic intervention, but also to the psychological effects of the setting.”

Authors: Manfred Spitzer, Markus Thimm, Leo Hermle, Petra Holzmann, Karl-Artur Kovar, Hans Heimann, Euphrosyne Gouzoulis-Mayfrank, Udo Kischka & Frank Schneide

Summary

In thought-disordered schizophrenic patients, the spread of activation in semantic networks is faster and farther than in non-thought-disordered schizophrenic patients and normal subjects, which is related to a decreased dopaminergic modulation. Psilocybin, which acts on the serotonin (5-HT) system, increases the spread of activation in semantic networks.

A double-blind, placebo-controlled study was conducted to assess the behavioral effects and pharmacokinetic properties of psilocybin.

To investigate how far activation spreads, word pairs of different semantic distance were presented in quick succession. The relation between the words affected the reaction time of the lexical decision of the latter, and the increased indirect priming effect was found to parallel decreases in objective performance measures.

We found that indirect semantic priming is highly sensitive to pharmacologic intervention, but also to the psychological effects of the setting of the study. This may account for the finding of consistent increases of priming effects under placebo.

In conclusion, we have demonstrated that a hallucinogenic agent affects the 5-HT system and can be linked with psychological measurements.