Unilateral neglect

Unilateral neglect is a disorder of attention where patients are unable to attend to stimuli, such as objects and people, located on one side of space. It most commonly results from brain injury to the right cerebral hemisphere, causing visual neglect of the left-hand side of space. Although most strikingly affecting visual perception (known as 'visual neglect'), neglect in other forms of perception can also be found, either alone, or in combination with visual neglect.

It may also present as a delusional form, where the patient denies ownership of a limb or an entire side of the body. Since this delusion often occurs alone without other signs of mental illness, it is often labeled as a monothematic delusion.

Overview
Unilateral neglect patients typically have no or limited conscious awareness of information coming from the neglected side of space. This lack of spatial awareness is similar to how a person is unaware of the blind spot in his or her vision. This might result in patients with unilateral neglect ignore stimuli from the neglected side of space, causing them to bump in to objects and to omit details on the left side when copying drawings. Notably, however, such patients will be unaware of the fact that they have missed out parts of the drawing.

In extreme cases, unilateral neglect patients will only attend to the left side of their body, shaving or adding make-up only to the non-neglected sides. In serious cases patients will unknowingly fail to move their left arms&mdash;often denying that the limb is theirs. Unilateral neglect is often seen as a form of anosognosia, a disorder where the patient is unaware of or denies the existence of their disability.

Causes
This disorder is a result of organic brain damage, usually centered around the right parietal or right parietal-occipital lobe. Right-sided brain injury usually causes neglect to the contralateral (opposite) side of space. This damage results in neglect or misperceptions of space opposite from the brain damage; usually the neglect is seen on the left with damage in the right hemisphere. Unilateral neglect may result from left hemisphere damage but this is rarer and is often less severe.

This disparity between left and right damage is thought to be caused by the fact that perceptive abilities and spatial attention are mostly lateralized in the right hemisphere1. As a result, the left hemisphere does not have the ability to compensate for the loss of right hemisphere function and can only attend to the right hand space.