A preliminary study of white matter disconnections underlying deficits in limb apraxia

Abstract

Limb apraxia is an acquired higher-order motor disorder affecting skilful actions, often observed following a stroke. It is assessed on tasks involving gesture production, recognition, imitation, object use, and multi-object sequencing. A two-system model for the organisation of action has been hypothesised based on errors patients make on these tasks. This distinguishes between deficits conceptualising actions mediated by an ‘indirect’ route to action, and deficits in implementing skilful actions, mediated via a ‘direct’ route. We tested 29 stroke patients with left hemisphere lesions on comprehensive apraxic tasks provided by the Birmingham Cognitive Screening. We employed white matter disconnection mapping, derived from patients’ structural T1 lesions and a diffusion-weighted dataset composed of 176 healthy participants, acquired with 7 T MRI scans from the human connectome project (HCP). Our analysis revealed that deficits in meaningless gesture imitation were associated with significant disconnection of the left and right occipital lobes via the splenium of the corpus callosum. This finding highlights a possible role of the right hemisphere in mediating ‘direct’ pathway- visuomotor deficits associated with apraxia. Though we did not identify a significant difference in tasks pertaining to an ‘indirect’ pathway in apraxia, there was a trend toward disconnection of the left fornix in gesture production tasks. Our results suggest separable disconnections associated with perceptual ‘direct’ and, possibly, more conceptual (memory-related) ‘indirect’ pathways. Further research with larger patient cohorts is needed to confirm and expand upon these findings, enhancing our understanding of the intricate neurobehavioural consequences of stroke, such as limb apraxia.