Forgetting from long-term memory in dementia and pure amnesia: role of task, delay of assessment and aetiology of cerebral damage.

This study investigated the hypothesis that memory disordered patients suffer of an exalted forgetting rate from long-term memory within the first few minutes following acquisition. For this purpose, we administered to groups of Alzheimer's (AD), Multi-infarct demented (MID), pure amnesic and age-matched normal controls a test involving immediate and 15-min delayed word-list recall and a modified version of the Huppert and Piercy's procedure (1978) assessing yes/no Recognition for pictures at 90 sec, 10 min, 1 hr and 24 hr delay intervals. Results showed an abnormal immediate/delayed performance decline for the word-list recall in AD and pure amnesic patients. In the same period, however, their Recognition score in the Huppert and Piercy's procedure decayed at normal rate. In the following intervals (1 hr and 24 hr), both groups disclosed abnormal forgetting slopes. Vascular demented patients, by contrast, disclosed fully normal forgetting rates both on the word-list recall and on the Huppert and Piercy's procedure. These findings are discussed in the light of cognitive mechanisms and neuroanatomical structures presumably underlying memory consolidation.