V9. Distinct contributions of dorsal and ventral streams to imitation of transitive and intransitive gestures: Evidence from acute stroke patients

Abstract

Background Meaningful gestures are one of the key features of social interaction and comprise both object-associated transitive movements (e.g. hammering) as well as intransitive movements referring to a communicative content (e.g. waving goodbye). The ability to imitate meaningful gestures is frequently impaired in apraxia due to left-hemispheric stroke. However, the pathophysiology behind these deficits so far remained unresolved. A dual stream-model for a dichotomized organisation of higher cognitive functions such as language or praxis has been proposed, with a dorsal stream involved in sensorimotor processing and a ventral stream for content and imagery. Aim of the study was to elucidate the role of the dual stream-model in imitation of meaningful movements using voxel-based lesion-symptom mapping (VLSM). Methods We performed VLSM in a sample of 136 left-hemispheric stroke patients (mean age ± SD 65 years ± 15, 83 male). Neuropsychological testing and MR-imaging were carried out in the acute phase after ischemic stroke (5.1 ± 1.9 days after symptom onset) to avoid interference with brain reorganization. Imitation deficits were assessed with a block of ten object-related movements and a block of ten communicative gestures presented by the examiner, patients were instructed to imitate the movement. Lesions were mapped on the diffusion-weighted image (if not available on Flair- image), statistical analysis with Brunner–Munzel Test was performed using non-parametric statistics implemented in MRIcron. Results Deficits in both, imitation of transitive and intransitive movements were associated with lesions in areas of the dorsal stream involved in motor control and action representations, such as the inferior parietal lobule, and the supramarginal gyrus. In addition to these common areas, deficits in imitation of intransitive movements showed a specific association with the superior and middle temporal lobe, whereas deficient transitive movements were also related to lesions within the ventral premotor cortex without involvement of temporal structures. Conclusion Deficits affecting imitation of transitive and intransitive gestures result from different and characteristic neuroanatomical lesion patterns. Our data suggest that imitation of transitive gestures depicting common tool-associated actions mainly involves stored motor programs and, thus, is mainly based on the dorsal stream. Conversely, imitation of intransitive communicative gestures additionally relies on the ventral stream, probably due to the higher semantic content, given the often symbolic character of intransitive gestures.