neurologic disorders
Overview of Cerebral Function
Pathophysiology of Cerebral Dysfunction
Cerebral dysfunction may be focal or global. Focal and global processes can manifest as deficits or become foci for seizure activity. These processes may also affect subcortical systems, altering arousal (eg, causing stupor or coma) or integration of thought (eg, causing delirium). Focal dysfunctionusually results from Structural abnormalities (eg, Overview of Intracranial Tumors , Manifestations depend on the lesion’s location, size, and development rate. Lesions that are<2 cm in diameter or that develop very slowly may be asymptomatic. Larger lesions, rapidly developing lesions (over weeks or months rather than years), and lesions that simultaneously affect both hemispheres are more likely to become symptomatic. Focal lesions in white matter can interrupt the connectivity between brain areas and cause the disconnection syndrome (inability to do a task that requires coordinated activity of≥2 brain regions, despite retention of basic functions of each region). Global dysfunctionis caused by Toxic-metabolic disorders, including hypoxia and ischemia (commonly) Diffuse inflammation Vasculopathy Major trauma Disseminated cancer Degenerative disorders Global dysfunction may also result from disorders that occur in a specific area of the brain (eg, abscesses, tumors, trauma) if they increase intracranial pressure or cause herniation. These disorders affect multiple dimensions of cerebral function. Recovery from brain injury depends in part on the following characteristics of the brain: Plasticity of the remaining cerebrum Redundancy Plasticity(ability of an area of the brain to alter its function) of the cerebrum varies from person to person and is affected by age and general health. Plasticity is most prominent in the developing brain. For example, if the dominant hemisphere language areas are severely damaged before age 8 years, the opposite hemisphere can often assume near-normal language function. Although capacity for recovery from brain injury is considerable after the first decade of life, severe damage more often results in permanent deficits. Gross reorganization of brain function after injury in adults is uncommon, although plasticity remains operative in certain specific areas of the brain throughout life. Redundancyrefers to the ability of more than one area of the brain to perform the same function. Specific syndromes include Agnosia None Amnesias (including Aphasia None Apraxia None Psychiatric conditions (eg, Depressive Disorders , 