A variety of spatial impairments affect patients undergoing neurorehabilitation. These range from right posterior parietal lesions that cause a hemineglect to the left parietal lesions of the Gerstmann syndrome that includes left/right confusion, finger agnosia, and the inability to report which finger is touched. Poor spatial localization by vision or touch may be detected on the patient's body, within the patient's peripersonal space, or beyond the patient's reach. Short-term or long-term spatial memory may be impaired. The neural network for these distributed functions includes the posterior parietal cortex, especially BA 7, which transforms visual, touch, and proprioceptive stimuli, the frontal eye fields and adjacent prefrontal cortex, and the cingulate region.99 Figure 9-6 shows the network effects of a thalamic infarction that deafferented the parietal region to produce contralateral spatial hemi-inattention.
Spatial information is represented by the patterns of firing of neuronal groups, which are sensitive, for example, to where a visual image falls on the retina, the angle of the head, and the location of the eyes in their orbits.365 The parietal regions project to the premotor cortex and putamen as an arm-centered and head-centered spatial coordinate system. Parietal projections also go to the frontal eye fields, superior colliculi, and other areas to control sac-cadic eye movements to locate objects in space, and send information to the entorhinal cortex, hippocampus, and DLFPC to hold memories about the location of items in space.
The sum of these functions allows the perception and recall of space. The posterior parietal regions seem to provide a holistic impression of space.99 They assist in planning and carrying out the visual and body-centered guidance for reaching and other visually guided behaviors. The multiple coordinate systems for vi-suomotor tasks, divided among at least a few bilateral brain regions, offer the potential for therapists to design interventions that work around a focal disruption of one pathway of spatial architecture. Strategies for treating hemi-inattention and related phenomena are discussed in Chapter 9.
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