Background We previously uncovered behavioural impairments in social cognition in Huntington’s Disease (HD) on the Animations Task, which requires participants to describe video-clips in terms of the movements and social interactions of geometric shapes. Few previous studies have explored neural responses to dynamic visual social stimuli in HD.

Aims This fMRI study explored neural activity in HD while patients viewed video-clips from the Animations Task. We expected to observe aberrant activity in brain areas involved in visual processing, motor function and social cognition in HD.

Methods Participants were 32 individuals with the HD gene, compared to 28 healthy controls. Three kinds of video-clips were shown during fMRI: random movement of two triangles (e.g. drifting), simple interactions (e.g. dancing) and complex social interactions (e.g. persuasion) between triangles. Participants categorised each video-clip as random movement/simple interaction/complex interaction.

Results Patients made more errors than controls when categorising complex interactions. For random movement clips, patients showed greater activity than controls in areas linked to visuo-spatial imagery, memory and perspective taking (precuneus; parahippocampal gyrus; paracingulate gyrus). For animations involving simple or complex interactions, hypoactivation was found in HD in brain regions linked to visual processing (occipital cortex), executive function (middle frontal gyrus), agency detection/mirror neurons (superior parietal lobe; premotor cortex), and social cognition (lateral orbitofrontal cortex; temporo-parietal junction). Contrasts based on video-clip type revealed reduced differentiation in neural responses according to the social content of the video-clips in HD. Viewing social interaction was associated with hypoactivation in brain areas crucial for social cognition alongside increased activity in areas involved in executive function.

Conclusions These findings highlight a loss of spontaneous neural sensitivity to dynamic visual social stimuli in HD. This could reflect reduced connectivity between brain areas involved in visual, motor and social-emotional processing, leading to poor recognition of non-verbal social cues and impaired inferences about social behaviour.