NONDOMINANT HEMISPHERE HIGHER CORTICAL DYSFUNCTION
When it comes to stroke-induced lateralized deficits, patients with left-sided hemiplegia caused by damage to the nondominant right cerebral hemisphere frequently do not recover as well as patients with similar left hemisphere lesions, despite the fact that they are not aphasic. Return to the work place and previous home and family participation occur less frequently after a stroke causing left-sided hemiplegia. Although disturbances of higher cortical function and behavior in patients with right hemisphere disease are more subtle, they are equally or more functionally disabling than the more obvious aphasia caused by left hemisphere disease. Deficits in right hemisphere disease include the following.
Constructional Dyspraxia. The right cerebral hemisphere, especially its inferior parietal lobe, is specialized for visual-spatial functions. Parietal lesions compromise the patient’s ability to draw and copy figures and diagrams, reproduce block designs or figures made with sticks or tongue blades, read a map, and follow or give directions to a given destination. Spontaneous drawings are complex and contain all appropriate details, but proportions, angles, and picture relationships are inaccurate, and the left half of the drawing often is omitted or minimized. Copying a figure does not significantly improve the performance.
Unilateral Spatial Neglect. Patients with right hemisphere lesions, especially those involving the frontal or parietal lobe or thalamus, often neglect objects, people, or sounds on their left side. They may also fail to adequately dress the left side of their body. When asked to read a headline or paragraph or examine a picture, they do not appreciate words or objects on the left. When instructed to bisect all lines on a piece of paper, patients with right hemisphere damage often divide the right side of the line and fail to cross lines on the left side of the page. Similar spatial neglect of the right side after left hemisphere damage is unusual.
Anosognosia and Blunted Emotional Responses. Patients who have right hemisphere damage often fail to recognize or acknowledge an obvious left-sided hemiplegia. Not only do they verbally deny weakness or fail to localize it to one side, but they may fall when attempting to walk. Furthermore, even when they admit the deficit, these patients seem not to be appropriately concerned or distressed, and generally are not discouraged about their uncertain future.
Testing of patients with right hemisphere lesions also shows that they have difficulty in appreciating the tone, mood, and emotional content of facial expressions or spoken language and miss nonlanguage cues. They also may be unable to invest their own voice or face with a given mood. Apathy and blunted recognition and transmission of emotional tone may hamper rehab litation and resumption of an active goal-oriented life.
Impersistence. Some patients with nondominant cerebral hemisphere damage are unable to persevere with a given task. A command that is quickly followed is just as quickly forgotten. When asked to keep their eyes closed, for example, or to cross off all A’s on a page, they begin the task correctly but soon abandon it. Questions are often answered before the query is complete. Impulsive behavior with little forethought and poor perseverance is also functionally disabling.
Other Dysfunctions. Damage to the right cerebral hemisphere can also affect either the ability to perceive rhythm, pitch, or tonality, or to read, write, or play music. Some patients have difficulty in recognizing familiar faces (prosopagnosia) and may be unable to visualize from memory the appearance of an object or a person. Loss of topographic recall of places and errors of localization or distance concerning buildings or geographic landmarks also occur.