Personal Hemineglect

Patients with hemineglect fail to direct attention and action toward the hemispace opposite their cerebral lesion. Neglect can affect either side, but it is more frequent, more severe, and more durable after right brain lesions. Hemineglect can disturb attention and action to the left side of extrapersonal space and external objects as well as to the left side of the patient's own body. Patients may fail to wash, comb, shave, and dress the left half of their bodies. They may forget about their frequently plegic left limbs and let them slip into uncomfortable and dangerous positions. When asked to touch their left arm, the reaching movement of the intact right hand may stop at the body midline or at the left shoulder.

It has been suggested that the basic disorder in hemineglect concerns the mental representation of space rather than either perceptual input or motor output. This line of thought leads to the prediction that if there exists a distinct mental represenation of one's own body, hemineglect can be restricted to the patient's own body. Empirical findings on this issue are inconsistent: One study found personal hemineglect without extrapersonal hemineglect in only 1 of 97 right brain-damaged patients, whereas the reverse dissociation occurred in 9 patients. Another study with a smaller sample of patients and using different tests of neglect found that one-third each of patients had predominantly extrapersonal, predominantly personal, and combined hemineglect. These studies were concerned with only relative differences of severity between personal and extrapersonal neglect, but there is one report of a patient showing severe personal hemineglect in testing as well as in spontaneous behavior but no extrapersonal hemineglect.

Although the previous studies invite the conclusion that personal and extrapersonal hemineglect are independent sequels of brain damage that happen to cooccur because of anatomical contiguity of causal lesions, functional interactions between them were demonstrated by varying the relationships between personal and extrapersonal definitions of left and right. In patients with left hemineglect blindfolded detection of touch of the left hand improves when the hand is placed across the body midline into the right hemispace. When the ulnar and radial edge of the left hand are touched simultaneously, neglect will affect the edge that happens to lie on the left side. Ulnar touch will be neglected when the hand is pronated and radial touch is neglected when the hand is supinated. Within a somatotopic representation of one's body, the left hand and its left side would be expected to be coded as being left regardless of their momentary position. The dependence of tactile sensation on hand position suggests an influence of position in peripersonal space on proprioceptive awareness.

In summary, studies of personal hemineglect lend support to the idea that the mental representation of one's own body is distinct from the mental representation of external space but demonstrate close proximity and functional relationships between them.

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