Article

It is well established that patients with hemispatial neglect present with severe
visuospatial impairments, but studies that have investigated visuomotor control
directly have revealed diverging results, with some investigations finding
impairments mirroring the perceptual difficulties of these patients, while others
have shown that such neglect patients perform relatively better in action tasks.
In this review we attempt to reconcile these diverging findings, addressing
differences in the type of visuomotor tasks studied but also highlighting the
diverging neuroanatomy that seems to be driving the differences in performance.
We argue that there are different types of actions and that these in turn depend
on different cortical networks (Goodale, Westwood, & Milner, 2004; Milner &
Goodale, 2006). Patients with visuospatial neglect, in contrast to patients with
optic ataxia, are relatively unimpaired at performing target-directed tasks even
towards stimuli located in their 'neglected' field. We relate these findings to
the view that for the on-line guidance of action, spatial information is coded in
egocentric coordinates and depends on the visuomotor networks of the visual
dorsal stream. Furthermore, based on recent lesion-symptom mapping studies, we
postulate that deficits in on-line actions that are observed after right-brain
damage are associated with damage to the visuomotor control network, in
particular with damage to the basal ganglia, frontal and parieto-occipital
regions. On the other hand, clear neglect-specific deficits emerge when the
action is off-line and not directly target-driven, thus requiring relational
metrics or scene-based coordinates (as is the case for example in delayed and
mirrored (anti-pointing) reaches). We review recent studies that support our
argument that such deficits in off-line actions are associated with damage to
occipito-temporal and parahippocampal cortex, perhaps as part of the ventral
visual stream or areas where information from the two visual streams is combined.
CI - Crown Copyright (c) 2011. Published by Elsevier Ltd. All rights reserved.

Langue : ANGLAIS