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What is amnesia?
Amnesia is a severe, isolated disturbance of declarative memory in the absence of other forms of cognitive dysfunction.
Patients are unable to acquire new memories (anterograde amnesia) or recall recent memories (retrograde amnesia).
Other memories remain intact, including remote memory, working memory, and semantic memory.
Injury to which areas can cause an amnestic syndrome?
Bilateral lesions of the Papez circuit and related areas can cause an amnestic syndrome, while unilateral lesions can produce a milder, but often clinically relevant, memory deficit.
The Papez circuit includes the medial temporal lobes (hippocampus and entorhinal cortex), the diencephalon (fornix and mammillary bodies; dorsomedial and anterior nuclei of the thalamus), and the basal forebrain cholinergic nuclei (medial septal nuclei and the diagonal band of Broca).
The isolated reduced ability to learn new information is referred to as amnestic mild cognitive impairment (aMCI). Many patients with aMCI develop Alzheimer’s dementia over the next 5 years.
