Diffuse dysfunction of the cerebrum, particularly the cerebral cortex, may cause abnormalities of the higher nervous system functions with or without involving the lower functions as well. For example, a common syndrome of diffuse cerebral cortical dysfunction called delirium, or encephalopathy, usually involves confusion with abnormal arousal, attention, orientation, or other higher neural functions, while often sparing the basic motor, sensory, and autonomic functions. Delirium is usually a reversible syndrome, where there is diffuse dysfunction of cerebral cortical neurons, which then subsequently recover when the cause is resolved. Dementia, or neurocognitive disorder, is another common group of syndromes, involving long-term, and usually progressive, cognitive loss from diffuse loss of cerebral cortical neurons.
Many types of pathology often cause diffuse cerebral syndromes, including genetic, idiopathic, vascular, epileptic, mechanical, metabolic, infectious, nutritional, and toxic disorders. Most of these primarily affect cognition, but some may also affect emotional functions or consciousness. Several genetic disorders may cause diffuse cerebral cortical dysfunction, such as Huntington’s disease, which often causes dementia from diffuse loss of cerebral cortical neurons. This also occurs with the idiopathic disorder Alzheimer’s disease, which is the most common cause of dementia. Several vascular abnormalities often cause a brief drop in blood pressure leading to a syndrome of diffuse cerebral cortical dysfunction called presyncope (feeling “faint”), or called syncope if there is loss consciousness (“fainting”). Seizures may involve most of the cerebral cortex at onset, which are called generalized seizures, or may be secondarily generalized from a focal seizure; either of these causes diffuse cerebral cortical dysfunction. The mechanical disorder head trauma may cause a brief episode of diffuse cerebral cortical dysfunction called concussion, or long-term, widespread diffuse traumatic brain injury. Many metabolic disorders, such as low blood sugar, are common causes of delirium. Certain microorganisms may invade brain tissue causing diffuse cerebral inflammation, which is called encephalitis, or may invade the cerebrospinal fluid and inflame the meninges, which is called meningitis. The nutritional disorder vitamin B12 deficiency may cause dementia. Many toxins may cause brain dysfunction, such as sedating medications that often cause delirium. Most types of mental illness, or psychiatric disorders, are probably from idiopathic diffuse cerebral dysfunction.