Affective Modulation of the Startle Eyeblink Reflex In Autism Spectrum Disorder In Response to Social and Non-Social Stimuli

Background:  Individuals with autism may have minimal or inappropriate affective response to social information yet can exhibit extreme affect to non-social aspects of their environment. An individual with autism may remain affectively flat when greeted by a familiar individual; however, respond enthusiastically at the sight of trains, road signs, or swirling water.  These variable reactions have been conceptualized in terms of affective dysregulation and have been linked to core symptoms of the disorder due to their potential effects on social development and inappropriate social interactions.  We have recently reported on anomalous affective responses to emotionally arousing images during a startle paradigm in an autism sample (Dichter et al., 2010). 

Objectives:  The purpose of the present study is to extend this line of research to examine responses to autism-relevant stimuli, namely faces and objects typically associated with circumscribed interests in autism (Sasson et al., 2008).

Methods: Participants with and without autism completed a startle eyeblink modulation session.  Each trial consisted of a 6s picture presentation during which acoustic startle probes (50ms, 100dB white-noise bursts with instantaneous rise times) were binaurally-presented via headphones 3500-5000 ms after picture onset.  Picture categories included negative, neutral, and positive IAPS images selected based on normative ratings of valence and arousal.  In addition, social images (i.e., images of closed-mouth NimStim faces with neutral expression) and non-social images (i.e., images related to circumscribed interests derived from Sasson et al., 2008) were presented as well.  To date we have assessed 6 typically developing individuals [mean age = 26.83] and 4 individuals with autism [mean age = 27.25]. By the annual IMFAR meeting in May 2011, we will have collected data on 20 individuals in each group.

Results: Peak EMG activity was calculated as the maximum response within a window of 10-250 ms following the acoustic probe and compared across picture categories.  In response to IAPS images, the typically developing group is displaying classic linear valence modulation patterns with increased responses to negative relative to positive images.  The autism group is showing preliminary evidence of anomalous eyeblink responses to IAPS images, relatively greater eyeblink response while viewing social stimuli, and relative decreased eyeblink responses to non-social stimuli associated with circumscribed interests in autism.

Conclusions: Preliminary analyses indicate anomalous eyeblink responses in individuals with autism in comparison to a typically developing sample to both standardized emotional stimuli and to autism-relevant stimuli.  The relatively increased eyeblink startle response to social images in the autism group suggests a heightened withdrawal response to this class of stimuli.  The relatively decreased eyeblink startle response to non-social circumscribed interest images in the autism group suggests greater approach motivation to this class of stimuli.  Implications for the social-motivation hypothesis of autism will be discussed.