Structural Disconnection of the Tool Use Network After Left Hemisphere Stroke Predicts Limb Apraxia Severity

Producing a tool use gesture is a complex process drawing upon the integration of stored knowledge of tools and their associated actions with sensory-motor mechanisms supporting the planning and control of hand and arm actions. Understanding how sensory-motor systems in parietal cortex interface with semantic representations of actions and objects in the temporal lobe remains a critical issue, and is hypothesized to be a key determinant of the severity of limb apraxia, a deficit in producing skilled action after left hemisphere stroke. We used voxel-based and connectome-based lesion symptom mapping with data from 57 left hemisphere stroke participants to assess the lesion sites and structural disconnection patterns associated with poor tool use gesturing. We found that structural disconnection between the left inferior parietal lobule, lateral temporal lobe (left middle temporal gyrus) and ventral temporal cortex (left medial fusiform gyrus) predicted the severity of tool use gesturing performance. Control analyses demonstrated that reductions in right-hand grip strength were associated with motor system disconnection, bypassing regions supporting tool use gesturing. Our findings provide causal evidence that limb apraxia may arise, in part, from disconnection of conceptual representations in the temporal lobe from mechanisms enabling skilled action production in the inferior parietal lobule.