The effect of a synthetic cannabinoid agonist (nabilone) on unimodal tactile illusion correlates with a psychometric scores in healthy volunteers.

Our previous studies showed that dexamphetamine, an indirect dopamine agonist, widens Stimulus Binding Windows (BWs) in healthy subjects. The present study aimed to investigate the effect of nabilone, a synthetic cannabinoid agonist, on the BWs in a unimodal illusion: the tactile funneling illusion (TFI). The study also aimed to study the association between tactile illusion with psychometric scores. Healthy participants (n = 32) completed the TFI at various delays and distances of separation of stimuli after receiving nabilone (2-4 mg, PO) or placebo in a randomized, double-blind, counterbalanced, crossover manner. The primary illusory measures were funneling and errors of localisation (EL). Three physiological and five psychometric measurements were also performed. The results showed that nabilone decreased funneling in a delay-dependent manner (p = 0.0016), whereby funneling was reduced at 0 ms (p = 0.01). Nabilone also significantly reduced EL in a distance-dependent manner (p = 0.038). Nabilone increased ratings on two of the five administered psychometric scales (p < 0.05), without significantly changing the overall (average) scores. However, there were associations between the overall psychometric scores and funneling under the strongest (0 ms delay) illusion condition, which is dependent on the drug condition (nabilone ρ = 0.45, p = 0.028). To conclude, unlike the effects of dexamphetamine, low activation of the cannabinoid system decreases the illusory perception of funneling, with narrowing spatial BWs.