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Humans look longer at preferred stimuli. This is also true for facial expressions of emotion. Here, we probed variations in the CNR1 gene for how it influences gaze duration to facial expressions of five basic emotions (happy, sad, angry, disgust, fear). The cannabinoid receptor 1 (CNR1) gene is a key component of the endocannabinoid system, which works with the mesolimbic dopaminergic pathways involved in processing rewards. In a previous fMRI study (Chakrabarti et al., 2006), we found that happy (but not disgust) faces trigger different degrees of reward-related neural activity, depending on the variant of CNR1 SNPs. We presume this is because brains differ genetically in the extent to which happy faces are treated as social rewards.
Objectives:
Variation (SNPs) in the CNR1 gene was predicted to be significantly associated with individual variability in gaze duration for happy faces.
Methods:
30 typical volunteers (13 males, 17 females, mean age 24.1 years) were genotyped for 4 SNPs (reported earlier) in CNR1, and tested on an emotion recognition paradigm (16 videoclips of 3s each for each of the 5 emotions, from MindreadingTM), while their gaze fixation time was recorded using ERICA (www.eyeresponse.com). Total gaze duration was measured for each stimulus.
Results:
Separate analyses of variance were performed for each SNP, with gaze duration as the dependent variable. This revealed two SNPs (rs806377 and rs806380) associated with differential gaze duration for happy (but not disgust) faces.
Conclusions:
The results converge with our earlier fMRI finding in suggesting that CNR1 is a key element in the molecular architecture of social reward perception. Our recent genetic association study of autistic traits and empathy in a typical sample found a significant association with CNR1. Together, this suggests an important role for CNR1 in social reward perception. This may implicate a role for it in underlying autistic traits.