Atypical somatosensory adaptation in adults on the autism spectrum: a high-density electrophysiological (EEG) mapping study.

Adaptation to repetitive sensory inputs promotes efficient neural processing by attenuating responses to redundant information and reallocating resources to novel stimuli. Reduced adaptation has been proposed to contribute to atypical sensory reactivity in autism, but the physiological mechanisms underlying tactile adaptation remain poorly understood. Here, we examined short-term adaptation to repetitive vibrotactile stimulation in autistic and neurotypical adults using high-density electrophysiological recordings. Fifty participants (18-44 years; 25 autistic; 25 neurotypical), received sequences of four brief vibrations to the index fingertip while viewing silent videos. Neural responses were analyzed for an early negative deflection (N1, [~]100 milliseconds) indexing basic stimulus recognition, and a later positive deflection (P2, [~]200-300 milliseconds) indexing higher-order contextual and attentional processing. Adaptation was quantified as changes in response magnitude across the four vibrations. The N1 did not differ between groups, showing minimal change across repetitions, indicating comparable processing of basic tactile features. In contrast, the P2 was significantly larger overall in the autistic group. Across both groups, responses to the first vibration in each sequence were greater than responses to subsequent vibrations, reflecting re-sensitization following the inter-sequence interval. Autistic participants exhibited consistently amplified P2 responses to initial vibrations, suggesting heightened re-sensitization rather than impaired within-sequence adaptation. Associations between neural responses and clinical measures of autistic traits and tactile sensitivity were modest. These findings indicate that autistic adults show amplified higher-order neural responses to tactile input alongside preserved short-term adaptation. Heightened re-sensitization to repeated touch may reflect shortened refractory periods, contributing to sensory hyper-reactivity and increased perceptual load.