The frontal lobe includes the motor cortex (areas 4, 6, 8, 44), the prefrontal cortex (areas 9-12 and 45-47), and the cingulate gyrus (p. 144). It is responsible for the planning, monitoring, and performance of motor, cognitive, and emotional functions (executive functions). Frontal lobe syndromes may be due to either cortical or subcortical damage and thus cannot be reliably localized without neuroimaging. The typical syndromes listed here are useful for classification but do not imply a specific diagnosis or exact localization of the underlying lesion.
Lateralized syndromes. Left frontal lobe lesions, depending on their location and extent, can produce right hemiparesis or hemiplegia, transcortical motor aphasia and diminished verbal output (p. 126), buccofacial apraxia (p. 128), and/or depression or anxiety. Right frontal lobe lesions can produce left hemiparesis or hemiplegia, left hemineglect (p. 132), mania, and/or increased psychomotor activity.
Nonlateralized syndromes. Fronto-orbital lesions produce increased drive, memory impairment with confabulation, and disorientation. Disinhibition and impaired insight into one's own behavior may produce abnormal facetiousness (German Witzelsucht), abnormal social behavior (loss of distance, sexual impulsiveness), indifference, or carelessness.
Lesions of the cingulate gyrus and premotor cortex produce syndromes ranging from abulia (loss of drive) to akinetic mutism (p. 120) and generally characterized by apathy, loss of interest, inertia, loss of initiative, decreased sexual activity, loss of emotion, and loss of planning ability. Urinary and fecal incontinence occur because of the loss of (cortical) perception of the urge to urinate and defecate. Altered voiding frequency or sudden voiding is the result. These patients are usually impaired in their capacity for divided attention (the processing of new information and adaptation to altered requirements, i.e., flexibility) and for directed attention (selective attention to a particular thing or task). Their attention span is short, they are easily distracted, they have difficulty in the execution of motor sequences, and they tend to perseverate (to persist in a particular activity or thought). Increased distractibility and prolonged reaction times impair performance in the workplace and in everyday activities such as driving.
Lesions of pathways. Lesions in pathways connecting the frontal lobe to other cortical and subcortical areas (p. 24) can produce frontal lobe-type syndromes, as can other diseases including multisystem atrophy, Parkinson disease, Alzheimer disease, normal-pressure hydro-cephalus, and progressive supranuclear palsy. Lesions of the corpus callosum. See p. 24.
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