Gamma Synchronization During Face Processing Is Associated with Social Motivation

Background:  ASD is characterized by deficits in social interaction and communication. EEG studies have demonstrated difficulties in face processing by individuals with ASD as evident by a delayed and diminished N170 response. This atypical N170 has been proposed as a secondary effect of a primary deficit in social motivation, which is considered a driving influence in the development of face expertise. Cheung et al. (2010) found that social personality traits (extraversion versus introversion) in typically-developing individuals modulated neural response to faces such that extraverts showed an enhanced face inversion effect. The present study further investigated the link between social motivation and face processing by examining gamma synchrony, which has been proposed as an indicator of long-distance interactions among neural regions. An alternative interpretation of face processing anomalies in ASD is that cognitive factors, rather than social motivation, could account for atypical face processing. Two previous studies have shown increased gamma synchrony in response to faces in typically-developing adults. Klopp et al. (2000) showed increased coherence 160-230 ms post-stimulus onset between the fusiform gyrus and other brain regions, and Rodriguez et al. (1999) showed increased synchrony between parieto-occipital and frontotemporal regions 200-260 ms post-stimulus onset.

Objectives:  The current study sought to contrast predictions of social versus cognitive influences on face perception. To study how social personality traits influence face-related activity, the relationship between gamma synchrony and social motivation was examined. The social motivation hypothesis would predict significant correlations between gamma synchrony and extraversion, while cognitive accounts would predict no relationship.

Methods: 96 typically-developing adults (34 male) were pre-screened with the Eysenck Personality Questionnaire Revised Short Scale (EPQ-R) for high or low (+/- 1 SD) scores on the extraversion subscale. 24 extreme scorers (14 extraverts, 10 introverts) viewed 60 trials each of upright and inverted faces, while EEG was recorded with a 128-channel Geodesic Sensor Net. EEG signals were decomposed to the gamma frequency band (30-50 Hz) using wavelet analysis based on 4-6 cycles, a 148 ms window size and 547.2 ms epochs, including a -25.6 ms baseline. Synchrony based on phase difference was calculated between all channel pairs and measured between 0 and 1, where 1 indicates two perfectly synchronized signals.  

Results:  ERP results indicated that the inversion effect significantly interacted with personality type: F (1, 22) = 5.11, p  = .03, MSE  = 0.86, η²_partial  = .19. Paired-sample t-tests revealed a significant difference in N170 amplitude between upright and inverted faces for the extraversion group, t (13) = 4.43, p  = .001, but no significant difference for the introversion group. Gamma analyses in progress reveal right-lateralized frontal/posterior coherence around 270 ms post-stimulus onset. We predict significantly greater synchrony in this time window in extroverted individuals.

Conclusions:  Results reflect the influence of social drive on face perception in typical development. This is the first study to demonstrate association between evoked gamma synchrony to faces and social personality traits. These findings parallel relationships observed in ASD and are consistent with the predictions of social motivation models of ASD.