Aim: Memorization comprises three stages: encoding, storage, and retrieval. Using neuropsychological tests, we investigated the stage at which encoding and storage are retained in Alzheimer's disease (AD) patients with progressive memory disorder.
Methods: The target patients were an amnestic mild cognitive impairment (MCI) group (21 cases) and FAST 4 (37 cases), 5 (10 cases), and 6 (4 cases) AD groups. The neuropsychological tests performed were the Rivermead behavioral memory test and Wechsler memory scale-revised. These were carried out in the MCI group as well as in each AD stage group. We investigated the delayed recall (free recall and cued recall) based on the disease stage and raw score of the sub-items in delayed recognition.
Results: The MCI group had 48% (median 0 point) correct respondents (providing ≥1 correct answer) for free recall, whereas FAST 4 and 5 groups had ≤14% correct respondents. In the verbal paired associates II evaluated in cued recall, the MCI group had 90% correct respondents, and the FAST 4, 5, and 6 groups had rates of 51%, 60%, and 50%, respectively. For the pictures and photos in the delayed recognition tasks, there were no significant differences in the percentage of correct respondents between the MCI group (100%) and the FAST 4 and 5 groups (70%-90%).
Conclusions: Given that retrieval is impossible if encoding and storage are impaired, we inferred that the encoding and retrieval abilities were retained even in moderately advanced AD.
Keywords: Rivermead behavioral memory test; Wechsler memory scale-revised; recall; recognition; storage.