Hemispatial Neglect - Causes

Causes

Brain areas in the parietal and frontal lobes are associated with the deployment of attention (internally, or through eye movements, head turns or limb reaches) into contralateral space. Neglect is most closely related to damage to the temporo-parietal junction and posterior parietal cortex. The lack of attention to the left side of space can manifest in the visual, auditory, proprioceptive, and olfactory domains. Although hemispatial neglect often manifests as a sensory deficit (and is frequently co-morbid with sensory deficit), it is essentially a failure to pay sufficient attention to sensory input. This is particularly evident in a related, but separate, condition known as extinction. A patient with extinction following right-hemisphere damage will successfully report the presence of an object in left space when it is the only object present. However, if the same object is presented simultaneously with an object in right space, the patient will only report the object on the right.

Neglect patients can also have problems with "interior" left information, since cases have been reported in which the patient when asked to describe something he knew before his brain damage describes only its right part.

Although hemispatial neglect has been identified following left hemisphere damage (resulting in the neglect of the right side of space), it is most common after damage to the right hemisphere. This disparity is thought to reflect the fact that the right hemisphere of the brain is specialized for spatial perception and memory, whereas the left hemisphere is specialized for language - there is redundant processing of the right visual fields by both hemispheres. Hence the right hemisphere is able to compensate for the loss of left hemisphere function, but not vice versa. Neglect is not to be confused with hemianopsia. Hemianopsia arises from damage to the primary visual pathways cutting off the input to the cerebral hemispheres from the retinas. Neglect is damage to the processing areas. The cerebral hemispheres receive the input, but there is an error in the processing that is not well understood.