Neurophysiological Correlates of Altered Motivation Towards Social and Non-Social Stimuli in ASD

Background:

In recent years the social motivation hypothesis of ASD (Chevallier, 2012) has gained popularity. Neuroimaging studies do not only suggest that individuals with ASD perceive social stimuli as less salient (Delmonte, 2012), but also that they show increased motivation towards non-social stimuli (Cascio, 2013). Directly comparing the neural response to social emotional versus non-social stimuli is therefore of great interest. The late positive potential (LPP) is a well suited neurophysiological measure for this purpose, as it represents motivational and attentional processes during the perception of social stimuli (Schupp et al. 2000). It is sensitive to the emotional content of stimuli and perceived relevance, and thereby related to the allocation of attentional resources (Schupp et al., 2004; Hajcak and Olvet, 2008; Ferrari et al., 2010).

Objectives:

The objective was to compare neural correlates of motivation and attention for social and non-social stimuli between children and adolescents with ASD and healthy controls.

Methods:

Participants viewed images of positive, negative and neutral emotional scenes involving humans, as well as neutral pictures of plants, while EEG was recorded. A one-back memory task was performed to sustain attention. Afterwards ratings of valence and arousal were obtained for all stimuli. The LPP was analyzed for each stimulus category as an area measure of 300-600 ms post stimulus onset at central, left and right posterior-parietal electrode clusters. LPP area measures and valence and arousal ratings were compared between groups using repeated measures ANOVAs (Between: Group ASD vs. CON, Within: Condition positive/negative/neutral/plant).

Results:

Analysis of a preliminary sample of 20 individuals with ASD and 10 controls (which were matched for age and IQ) indicate that children with ASD perceived negative emotional images as less arousing (p=.009), while plant pictures were rated as more arousing compared to controls (p=.040). Valence ratings also showed that the ASD group rated the negative emotional pictures as less negative (p=.040), and found plant stimuli just as pleasant as positive emotional stimuli (p_ASD =1.0, p_CON=.005). Looking at the LPP a group by condition interaction was found in the right hemisphere (F[3,84]=2.8; p=.043). Post-hoc tests suggested that this might have been due to higher LPPs for plant stimuli in the ASD compared to the control group (p=.091, Mean_ASD=5714.3±2995.5 μV*ms; Mean_CON=3812.6±2362.2 μV*ms).

Conclusions:

These preliminary results indicate that individuals with ASD do indeed perceive social emotional and non-social stimuli differently. This pattern is also confirmed by an increased LPP response for non-social stimuli. These findings expand existing evidence by showing that the LPP is not only increased for non-social stimuli that are of special interest to individuals with ASD (Benning, 2016), but also for other seemingly random non-social objects like plants.