Memory impairment in amnesia and dementia: implications for the use of animal models.

Cases of amnesia, in which there is a stable memory impairment with sparing of other cognitive functions, have taught us a great deal about the neuroanatomic basis of memory storage and retrieval; animal models of amnesia have provided even more precise information about the brain mechanisms responsible for specific aspects of memory functioning. Amnestic syndromes are rare, however, and constitute only a tiny fraction of the clinical cases in which memory is impaired. Dementia, particularly that due to Alzheimer's disease, is much more common but differs from the amnestic syndromes in three important ways: (1) a variety of of cognitive functions including language and praxis are affected, (2) the condition is usually progressive with gradual loss of several neuronal populations, and (3) the etiology of dementia is not well understood at present but clinical data suggest some role for genetic, viral, vascular and toxic environmental factors. It is argued that animal models should give greater attention to these important features of the common clinical dementias.