Background: Prader-Willi syndrome (PWS) is a complex genetic neurodevelopmental disorder with endocrine disturbances, hyperphagia and often life-threatening obesity as key features. We investigated emotional-processing of food and eating behavior in PWS using startle response-modulation. Startle eyeblink response is an involuntary reflex activated by the autonomic nervous system in response to sudden or disturbing auditory/visual stimuli which may be modulated by the emotional valence of concurrently viewed visual stimuli.
Methodology: Differences in affective modulation of startle reflex were recorded in 13 individuals with PWS versus 8 healthy controls when viewing standard neutral, negative, positive and food-derived images. Electromyogram (EMG) of the orbicularis oculi muscle was measured in response to binaural white noise before and after consumption of a standard 500 Kcal meal. Participants reported their perceived emotional valence for each image, pre- and post-meal, using a 1-10 Likert rating scale.
Results: Subjective ratings of food images and urge to eat were significantly higher in PWS than controls and did not significantly decline post-meal. Acoustic startle responding was detected in PWS but was significantly lower than control participants under all conditions. Startle responses to food images in PWS were attenuated relative to other picture types with potentially abnormal emotional modulation of responses to non-food images which contrasted self-reported picture ratings. A stable positive emotional valence to food images was observed pre- and post-feeding with a sustained urge to consume food in PWS.
Conclusions: Emotional processing measured using startle modulation in response to non-food images was abnormal in PWS which may reflect unique physiological attributes such as hypotonia and abnormal skin conductivity due to increased fat mass. Alternatively, disruption of autonomic or sympathetic nervous system functioning reported in PWS may impact on hunger and/or food drive states. Our findings parallel attentional/processing attributes of affective stimuli reported in autism spectrum disorder and support the feasibility of eyeblink startle modulation to assess food motivation in PWS and provide preliminary data to optimize methodological parameters.