Body Perception: Disorders

Personal Neglect and Associated Phenomena

Hemispatial neglect is a common consequence of stroke, particularly to the brain's right hemisphere, but also occurs on occasion following left hemisphere stroke, as well as subsequent to traumatic brain injury or tumor. Patients with neglect fail to attend to or act in the side of space opposite the brain lesion and may fail to attend to one side of their bodies. Thus, for example, patients with left neglect caused by right hemisphere lesions may fail to wash their left hands, comb their hair on the left of their heads, or shave the left sides of their faces. Even when looking in a mirror, they frequently fail to recognize that the left side of the body is poorly attended. This is known as personal neglect.

A well-known phenomenon in the neglect syndrome is that of tactile, auditory, or visual extinction. It has recently been demonstrated that the extinction phenomenon is observed within single body parts. For example, if a neglect patient is touched simultaneously in two spots on the back of the same hand, one spot slightly to the left of the other, he or she will frequently only report the right-most touch. There is thus a “gradient” of attention that spans individual body parts.

Neglect patients often exhibit anosognosia for (i.e., unawareness of) their motor and spatial deficits. For example, patients with weakness of an arm or leg after stroke may frankly deny that there is a problem, even when asked to demonstrate the limb's function. Finally, and less commonly, patients with neglect may exhibit somatoparaphrenia, or delusions that the limbs on the side of the body opposite the stroke do not belong to them, and may even belong to others. It is not known precisely how such body-related delusions may emerge, but it is likely that they are the product of a mismatch between intact and damaged parietal lobe sectors that code different aspects of perception and action of the limbs.

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