Dysfunctional neural processing of object-related speech with semantically unrelated vs related co-verbal gesture in...

Schizophrenia spectrum disorders (SSD) are accompanied by impaired multimodal communication. This is particularly evident in production and comprehension deficits of both speech and gesture. Previous neuroimaging findings indicate reduced activation in sensorimotor regions, such as the left postcentral gyrus and right insula, during object-related speech processing in SSD (He et al., 2021). However, it remains unclear how semantic congruency of co-verbal gestures influences the neural processing of object-related speech. This study aims to investigate the effect of semantically related and unrelated gestures on the processing of social and object-related speech.

45 patients with SSD and 43 healthy controls viewed short videos of an actor presenting social or object-related sentences, accompanied by semantically related or unrelated emblematic (social-related) and tool-use (object-related) gestures. Functional MRI data was acquired while participants performed a content-judgment task, deciding whether the observed stimuli contained social or object-related information.

Object-related stimuli and semantically related gesture were associated with higher accuracy rates in the content-judgment task in both groups. When processing object-related content with unrelated gestures, patients displayed reduced neural activation in a cluster including the supplementary motor area and the precentral, superior frontal, posterior orbital and temporal gyri, as compared to healthy controls.

These results extend findings on motor-simulation in object-related information, potentially reflected in motor cortex activation for object-related sentences in healthy controls. Patients with SSD demonstrated reduced premotor cortex activation especially when the object-related speech was accompanied by semantically unrelated gestures, suggesting a specific impairment in mental simulation.