Abstract
Acute administration of the primary psychoactive constituent of cannabis, Δ-9-tetrahydrocannabinol (THC), impairs human facial affect recognition, implicating the endocannabinoid system in emotional processing. Another main constituent of cannabis, cannabidiol (CBD), has seemingly opposite functional effects on the brain. This study aimed to determine the effects of THC and CBD, both alone and in combination on emotional facial affect recognition. 48 volunteers, selected for high and low frequency of cannabis use and schizotypy, were administered, THC (8mg), CBD (16mg), THC+CBD (8mg+16mg) and placebo, by inhalation, in a 4-way, double-blind, placebo-controlled crossover design. They completed an emotional facial affect recognition task including fearful, angry, happy, sad, surprise and disgust faces varying in intensity from 20% to 100%. A visual analogue scale (VAS) of feeling ‘stoned’ was also completed. In comparison to placebo, CBD improved emotional facial affect recognition at 60% emotional intensity; THC was detrimental to the recognition of ambiguous faces of 40% intensity. The combination of THC+CBD produced no impairment. Relative to placebo, both THC alone and combined THC+CBD equally increased feelings of being ‘stoned’. CBD did not influence feelings of ‘stoned’. No effects of frequency of use or schizotypy were found. In conclusion, CBD improves recognition of emotional facial affect and attenuates the impairment induced by THC. This is the first human study examining the effects of different cannabinoids on emotional processing. It provides preliminary evidence that different pharmacological agents acting upon the endocannabinoid system can both improve and impair recognition of emotional faces.
Highlights
Decoding basic human emotional expressions is a key adaptive skill that allows for the prediction of future behaviour and is essential for social communication, interpersonal relationships and mental health (Carton et al, 1999)
There was a main effect of schizotypy on scores on the Schizotypal Proneness Questionnaire (SPQ) (F(1,44)=12.47, po0.001), Beck Depression Inventory (BDI) (F(1,43)=14.70, po0.001) and State Trait Anxiety Inventory (STAI) (F(1,44) =9.05, p= 0.004) where the high schizotypy group had higher scores than the low schizotypy group for each measure
To test the hypothesis that THC+CBD would protect against the negative effects of THC here, we conducted a paired-samples t-test between THC and THC+CBD at 40% which revealed that participants were more accurate on THC+CBD (M=43.52%, SD=10.9%) compared to THC alone (M=39.75%, SD=4.51%) (t(46)= À 2.33, p=0.024)
Summary
Decoding basic human emotional expressions is a key adaptive skill that allows for the prediction of future behaviour and is essential for social communication, interpersonal relationships and mental health (Carton et al, 1999). Cannabis and its main active ingredient, Δ-9tetrahydrocannabinol (THC) produce euphoria and cognitive impairments (Curran et al, 2002; Fernández-Serrano et al, 2011) alongside transient negative emotional states such as anxiety and paranoia (D'Souza et al, 2004) These emotionbased changes suggest the endocannabinoid system is involved with emotional processing. Cannabis consists of over 100 cannabinoids, the two most abundant being THC, a partial agonist at the CB1 receptor (Pertwee, 2008) and cannabidiol (CBD) which has a complex mode of action involving several receptor, re-uptake and enzymatic proteins It inhibits the reuptake and hydrolysis of the endocannabinoid, anandamide (Pertwee, 2008). These cannabinoids have opposing psychological and emotional properties, for example, whilst THC can induce acute anxiety (Martin-Santos et al, 2012) and amnesic effects (Curran et al, 2002), CBD may have some anxiolytic effects (Guimaraes et al, 1990) and has been shown to block THC-induced memory impairments (Morgan et al, 2010b; Englund et al, 2013)
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