Thursday, October 27, 2011

Unilateral Spatial Neglect

Unilateral spatial neglect is a clinical syndrome in which patients are unaware of entire sectors of space on the side opposite to their lesion. These patients may neglect parts of their own body, parts of their environment, and even parts of scenes in their imagination. Unilateral spatial neglect (also known as hemispatial neglect) is produced by a lateralized disruption of spatial attention and representation and raises several questions of interest to cognitive neuroscientists. How do humans represent space? How do humans direct spatial attention? How is attention related to perception? How is attention related to action?

Spatial attention and representation can also be studied in humans with functional neuroimaging and with animal lesion and single-cell neurophysiological studies. Despite the unique methods and approaches of these different disciplines, there is considerable convergence in our understanding of how the brain organizes and represents space. Distributed neuronal networks clearly mediate spatial attention, representation, and movement. Focal damage to parts of these networks can produce subtle differences in deficits of these complex functions. These differences themselves are of interest. A careful study of spatial attention and representations through the syndrome of spatial neglect is possible precisely because neglect is heterogeneous.

Personal neglect refers to neglect of contralesional parts of one’s own body. Observing whether patients groom themselves contralesionally provides a rough indication of personal neglect. Patients who ignore the left side of their body might not use a comb or makeup, or might not shave the left side of their face (Beschin & Robertson, 1997). To assess personal neglect, patients are asked about their left arm after this limb is brought into their view. Patients with left personal neglect do not acknowledge ownership of the limb. When asked to touch their left arm with their right hand, these patients fail to reach over and touch their left side. A phenomenon called anosognosia for hemiplegia can also be thought of as a disorder of personal awareness. In this condition, patients are aware of their contralesional limb, but are not aware of its paralysis. Anosognosia for hemiplegia is not an all-or-none phenomenon, and patients may have partial awareness of their contralesional weakness. Misoplegia is a rare disorder in which patients are aware of their own limb, but develop an intense dislike for it.