neurologic disorders
Amnesias
Etiology of Amnesias
Amnesia can result from diffuse cerebral impairment, bilateral lesions, or multifocal injuries that impair memory-storage areas in the cerebral hemispheres. Predominant pathways for declarative memory are located along the medial parahippocampal region and hippocampus as well as in the inferomedial temporal lobes, orbital surface of the frontal lobes (basal forebrain), and diencephalon (which contains the thalamus and hypothalamus). Of these structures, the following are critical: Hippocampal gyri Hypothalamus Nuclei of the basal forebrain Mediodorsal thalamic nuclei The amygdaloid nucleus contributes emotional amplifications to memory. The thalamic intralaminar nuclei and brain stem reticular formation stimulate the imprinting of memories. Bilateral damage to the mediodorsal nuclei of the thalamus severely impairs recent memory and the ability to form new memories. Amnesia may be caused by Thiamin deficiency (by causing Wernicke Encephalopathy or Traumatic Brain Injury (TBI) None Seizure Disorders None Global brain anoxia or ischemia Encephalitis None Embolic occlusion at the top of the basilar artery, causing ischemia in the anterior medial temporal lobes Degenerative Dementia such as Various drug intoxications (eg, chronic solvent sniffing,amphotericin Borlithiumtoxicity) Hypothalamic tumors Psychologic trauma or stress Wernicke-Korsakoff syndrome is a form of amnesia that combines Wernicke Encephalopathy and Posttraumatic amnesias for the periods immediately before and after concussion or moderate or severe head trauma seem to result from medial temporal lobe injury. Moderate or severe trauma may affect larger areas of memory storage and recall, as can many diffuse cerebral disorders that cause dementia. Psychologic disturbances of memory (as occurs in Dissociative Amnesia ) result from extreme psychologic trauma or stress. Age-associated memory impairment(benign senescent forgetfulness) refers to the memory loss that occurs with normal aging. People with benign senescent forgetfulness gradually develop noticeable problems with memory, often first for names, then for events, and occasionally for spatial relationships. Objective cognitive tests are usually show normal or indicate minimal deficit. Benign senescent forgetfulness has no proven relationship to dementia, although some similarities are hard to overlook. Amnestic mild cognitive impairment(amnestic MCI) may be present in people who have a subjective memory problem, who do worse on objective memory tests, but who otherwise have intact cognition and daily function. People with amnestic MCI are more likely to develop Alzheimer disease than age-matched people without memory problems. 