Mapping brain function underlying naturalistic motor observation and imitation using high-density diffuse optical tomography
Background: While autism spectrum disorder (ASD) is defined by deficits in social communication with restricted interests and repetitive behaviors, autistic individuals often show early impairments in motor imitation that persist through childhood and into adulthood. High-density diffuse optical tomography (HD-DOT) overcomes logistical challenges of functional magnetic resonance imaging (fMRI) to provide an open scanning environment conducive to neuroimaging during naturalistic motor imitation. Additionally, the mirror neuron system (MNS) is crucial for understanding and imitating actions, and its dysfunction is hypothesized to underlie key ASD features. Objective: We aim to investigate brain function underlying motor observation and motor imitation in adult autistic and non-autistic individuals (NAI). We hypothesize that HD-DOT will reveal greater MNS activity during motor imitation than motor observation, and that MNS activity will exhibit a negative correlation with autistic traits. Methods: We imaged brain function using HD-DOT in N=100 participants as they passively observed videos of an actor completing sequences of meaningless arm movements. Additionally, while being simultaneously recorded with both HD-DOT and Kinect 3D cameras for computer-vision-based assessment of motor imitation (CAMI), participants imitated different videos of an actor completing similar arm movements. Responses to the tasks were estimated using general linear models, and multiple regression was used to investigate brain-behavior associations with autistic traits, using the Social Responsiveness Scale, and imitation fidelity as measured with CAMI. Results: Both motor observation and imitation tasks elicited significant activations in visual, temporal, and MNS areas, with imitation showing stronger activation in motor regions. Notably, MNS regions exhibited greater activation during observation than imitation. Additionally, activity during observation in the right parietal lobe correlated with autistic traits assessed with the SRS. Conclusions: Our findings provide robust evidence of shared and task-specific neural mechanisms underlying motor observation and imitation, emphasizing the differential engagement of MNS regions during motor observation and imitation.