University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

459

Pages:

2
Author:

Mariam A.

episodic memory system Neuroanatomical structures  Medial temporal lobes. o Hippocampus. o Entorhinal and perirhinal cortices.  Diencephalon. o Mammillary bodies. o Dorsomedial nucleus of the thalamus. o Forms part of a circuit connected to the MTL region.  Basal forebrain. o Medial septal nucleus o The diagonal band of Broca and nucleus Basalis of Meynert. o Project to the cortex and hippocampus.  Lesion in anyone of these structures can cause characteristic impairment of the episodic memory system; amnesic syndrome.  Chronic global amnesia (impaired performance whether the material to be remembered is visual or verbal) requires bilateral lesions.  Material specific memory disorder arise with localised lesions on the right (impaired visual memory) or left (impaired verbal memory). Clinical correlation: amnesic syndrome  Bilateral lesions in these brain structures results in a classic “Amnesic syndrome”.  Presentation: o Consistent inability to retain novel information (anterograde amnesia). o Variable ability to remember information already stored in long-term memory (retrograde amnesia). o Preservation of IQ, social skills. o Preservation of immediate memory. o Preservation of semantic memory. o Preservation of procedural memory.  Aetiology: o Various disorders give rise to an “Amnesic syndrome”. o Groups are classified by site of pathology. Mediotemporal lobe amnesia  Classical case – H.M. o Underwent surgery for intractable seizures; bilateral resection of portions of the hippocampus, hippocampal gyrus, uncus and amygdala. o Consequence: dense and pure amnesia; “time stopped”. o Furthermore, impairments in STM, IQ, reading, writing and calculating, and procedural skills were not observed.  Amnesia secondary to anoxia: o Anoxia occurs due to cardiac arrest, near drowning, hanging, carbon monoxide poisoning.     o Although it results in widespread brain damage, the medial temporal lobes are particularly sensitive to oxygen deprivation. o Area CA1 of the hippocampus is particularly sensitive. Dementia: o Several different types are associated with a primary memory deficit. o Compromises function of the medial temporal lobe and forebrain structures. Amnesia associated with herpes simplex encephalitis: o Most common form of viral encephalitis in the US. o Associated with type 1 of the virus. o Symptoms include headache, fever, vomiting, confusion. o Rapidly progressing; 24 hours leading to severe brain damage. o Problem: severe anterograde and retrograde amnesia. o Some semantic memory impairment. Amnesia associated with paraneoplastic limbic encephalitis. o Autoimmune response to cancer elsewhere in the body. o Associated malignancy oat cell carcinoma of the lung. o Disorder typically occurs in 50 – 70. o Problem: severe anterograde amnesia and affective disorder. Transient global amnesia: o Temporary in nature. o Onset is abrupt lasting minutes – 24 hours. o Men and women equally represented. o Severe anterograde amnesia, and patch retrograde amnesia. o Personal identity and semantic knowledge intact. o Aetiology unknown, but not related to TIA, but usually follows intense activity.