Restricted neural parametric modulation of emotional arousal in autism reveals a core role for the cerebellum.

Understanding how emotional arousal and valence are processed in autism spectrum disorder (ASD) is key to uncovering underlying affective mechanisms. Prior research has yielded mixed results, particularly regarding arousal. Using functional magnetic resonance imaging (fMRI), we examined neural responses to emotional video clips in adults with ASD (n = 20) and typically developing controls (n = 20). Stimuli were designed to elicit controlled emotional responses with standardized visual and narrative features, and parametric modulation analyses assessed neural activation as a function of self-reported arousal and valence. Behavioral ratings confirmed stimulus validity. For arousal, typically developing individuals showed widespread modulation across frontal, parietal, temporal, and subcortical regions, including the cingulate gyrus, insula, caudate, and ventral tegmental area. In contrast, ASD participants exhibited restricted modulation, primarily within the anterior cerebellum. No group differences emerged for valence, with both groups recruiting frontal and limbic regions such as the amygdala and insula. These findings highlight a dissociation between arousal and valence processing in ASD. Reduced cortical engagement and increased anterior cerebellar (including the vermis) involvement during arousal suggest compensatory mechanisms, underscoring the importance of distinguishing emotional dimensions when characterizing neural processes in autism.