Hemineglect is an abnormality in attention to one side of the universe that is not due to a primary sensory or motor disturbance. In sensory neglect, patients ignore visual, somatosensory, or auditory stimuli on the affected side, despite intact primary sensation (see Neuroanatomy through Clinical Cases, Chapter 19). This can often be demonstrated by testing for extinction on double simultaneous stimulation. Thus, patients may detect a stimulus on the affected side when presented alone, but when stimuli are presented simultaneously on both sides, only the stimulus on the unaffected side may be detected. In motor neglect, normal strength may be present, however, the patient often does not move the affected limb unless attention is strongly directed toward it. Sensory and motor neglect are usually tested as part of the visual, auditory, somatosensory, and motor exams. During the reading and writing portions of the language exam, patients may be noted to neglect one side of the page.
During the mental status exam, certain other aspects of neglect should be screened for. Patients should be asked, "Is anything wrong with you right now?" because patients with anosognosia may be strikingly unaware of severe deficits on the affected side. For example, some patients with acute stroke who are completely paralyzed on the left side believe there is nothing wrong and may even be perplexed about why they are in the hospital. Some patients do not even comprehend that affected limbs belong to them (hemi-asomatognosia). In addition, certain drawing tasks, such as asking the patient to bisect a line or draw a clock face, can demonstrate neglect. Construction tasks involving drawing complex figures or manipulating blocks or other objects in space may be abnormal as a result of neglect or other visuospatial impairments. However, constructional abilities can also be abnormal because of other cognitive difficulties, such as impaired sequencing (see next section) or apraxia.
Hemineglect is most common in lesions of the right (nondominant) parietal lobe, causing patients to neglect the left side. Left-sided neglect can also occasionally be seen in right frontal lesions, right thalamic or basal ganglia lesions, and, rarely, in lesions of the right midbrain. In left parietal lesions a much milder neglect is usually seen affecting the patient's right side. Abnormal constructions demonstrating neglect can occur with right parietal lesions. In addition, other abnormalities in constructions can occur as well, as a result of lesions in many other parts of the brain. Generally, however, impaired visuospatial function is more severe with damage to the nondominant (right) hemisphere.