Multi-modal and bi-directional effects of a synthetic Δ9-Tetrahydrocannabinol (THC) analogue, Nabilone, on spatio-temporal binding windows: Evidence from the projected hand illusion.

A single-blind, placebo-controlled crossover study tested whether a synthetic THC analogue, Nabilone (1-2 mg), alters the sense of agency and body ownership in 32 healthy volunteers, comparing effects to those previously seen in schizophrenia. The study found that Nabilone had multimodal and bidirectional effects on the projected hand illusion, widening the spatio-temporal binding window in some participants and narrowing it in others, depending on spatial and temporal conditions. Evidence supported a unitary spatio-temporal binding window rather than separate spatial and temporal windows. No significant associations were found between agency and embodiment measures, and a large proportion of participants did not experience the illusion.

Study at a glance

Abstract

Abnormally widened spatial and temporal binding windows (SBW/TBWs; length of space/time whereby stimuli are considered part of the same percept) are observed in schizophrenia. TBW alterations have been associated with altered sense of agency (hereafter referred to as agency), and an associative relationship between embodiment (body ownership) and agency has been proposed. SBWs/TBWs are investigated separately, but no evidence exists of these being separate in mechanism, system or function. The underlying neural substrate of schizophrenia remains unclear. The literature claims either pro-psychotic or anti-psychotic effects of Δ9-Tetrahydrocannabinol (THC) in patients and healthy individuals, but major support for cannabis in the aetiology of schizophrenia is associative, not causal. To clarify if THC is pro- or anti-psychotic, this single-blind, placebo-controlled within-subjects cross-over study tested several hypotheses. 1) Competing hypotheses that a synthetic THC analogue, Nabilone (NAB, 1-2 mg), would alter measures of agency and embodiment in healthy volunteers (n = 32) similarly, or opposite, to that of in patients with schizophrenia. 2) That there would be significant associations between any NAB-induced alterations in individual agency and embodiment measures in the Projected Hand Illusion (PHI). 3) That there is a unitary spatio-temporal binding window (STBW). A large proportion of individuals did not experience the PHI. Multimodal and bi-directional effects of NAB on the PHI were observed. Evidence of a unitary spatio-temporal binding window (STBW) was observed. NAB widened the STBW in some but narrowed it in others as a function of space and delay. No associations were found between agency and embodiment.