Effects of varied doses of psilocybin on time interval reproduction in human subjects

This double-blind, placebo-controlled, within-subjects study (n=21) investigated the effects of psilocybin (0.84, 8.05, & 17.5mg/70kg) on time perception and found that it increased the loss rate of internal time representation even within the microdose range. This may indicate psilocybin’s subjective effects, such as the experience of ‘time standing still’.

Abstract

“Introduction: Awareness of temporal order of events and the ability to discriminate temporal durations are typical for the normal, wakeful conscious state, whereas alterations of subjective time experience are often observed in so-called ‘altered states of consciousness’ (ASC).

Methods: Action of a hallucinogenic substance, psilocybin, on internal time representation was investigated in two double-blind, placebo-controlled studies: Experiment 1 with 12 subjects and graded doses, and Experiment 2 with 9 subjects and a very low dose. The task consisted in repeated reproductions of time intervals in the range from 1.5 to 5 s. The effects were assessed by parameter κ of the ‘dual klepsydra’ model of internal time representation, fitted to individual response data and intra-individually normalized with respect to initial values.

Results: The estimates κˆ were in the same order of magnitude as in earlier studies. In both experiments, κ was significantly increased by psilocybin at 90 min from the drug intake, indicating a higher loss rate of the internal duration representation.

Discussion: These findings are tentatively linked to qualitative alterations of subjective time in altered states of consciousness.”

Authors: Jiří Wackermann, Marc Wittmann, Felix Hasler & Franz X. Vollenweider

Summary

Psilocybin induces psychosis-like states, which are good experimental models for testing concepts and hypotheses concerning ‘subjective time’ and, particularly, models of internal time representation. Psilocybin significantly impaired subjects’ ability to synchronize to inter-beat intervals longer than 2 s, and slowed down their preferred tapping rate.

An alternative strategy is to study the subject’s response function across the whole range of stimulus durations, using a suitable parametric model. The dual klepsydra model (DKM) of duration reproduction consists of two inflow – outflow units (IOUs), allocated for the representation of duration perceived during the ‘presentation’ phase and the ‘reproduction’ phase, respectively. The DKM is not a computational device, but rather a primitive comparator of two elapsed time intervals, built upon elementary biophysical principles.

Postulate equal inflow rates, i1 = i2 , and w being constant by experimental design. The form of the response function is determined solely by parameter , and can be estimated by minimizing the weighted sum of squared errors.

Data from two double-blind, placebo-controlled studies are reported. The progressive shortening phenomenon is seen as a negative curvature of reproduction curves, and clearly revealed by r/s -versus-s data plots.

In Experiment 1, subjects were presented with 500 Hz tones for 1.5, 2, 2.5, 4, 4.5, and 5 s, and had to switch off the tone by pressing a key when the duration of the second tone was subjectively equal to that of the first tone.

Nine of the 108 data sets were unavailable due to a computer failure. The remaining 103 data sets were in good agreement with other DRT studies, and 14 cells were missing from the data matrix.

For all subjects in all conditions, q0 = q90 = q240 = 1 was used to replace missing values when the geometric mean of the two known values was unavailable.

At the time of the maximal drug action, 90 min from intake, the medium dose of psilocybin slightly increased q’s w.r.t. the initial value 0 or the placebo value 90.

In Experiment 1, psilocybin increased the value of by 16%, whereas in Experiment 2, psilocybin significantly increased the value of by 44%. The effect was observed at a very low dose of psilocybin, which barely affected self-reported subjective experience.

Experiments 1 and 2 were carried out with groups of participants differing significantly in their age. Older subjects may show higher sensitivity to psilocybin in terms of cognitive effects.

A dual klepsydra model was used to study time perception in the supra-second domain. Psilocybin was found to increase the loss rate of internal time representation, and the DKM parameter is a sensitive measure of effects of psychoactive substances upon the internal representation of time.