Verbal memory disorders in Alzheimer's disease and multi-infarct dementia

Abstract

On the basis of theoretical reasons, it could be predicted that Alzheimer's disease (AD) and Multi-infarct Dementia (MID) would provoke a different pattern of neuropsychological impairment, with a prevalent disruption of episodic memory in AD patients. This finding had not been obtained in previous investigations, but this negative result could be due to the confounding effect of the greater severity of dementia usually observed in AD patients. The main purpose of the present research therefore consisted in comparing results obtained on various indices of verbal memory by two groups of AD and MID patients carefully matched as for the overall severity of dementia. With this aim in mind, a test of verbal memory (the Rey's 15 words memory test), allowing patients to obtain scores of immediate and delayed recall and of delayed recognition, was administered to 50 normal controls and to 41 AD and 35 MID patients, carefully matched as for the overall severity of dementia. Both quantitative and qualitative differences were observed between the two diagnostic groups of dementia. From the quantitative point of view, AD patients scored significantly worse than MID patients on measures of immediate recall, delayed recall and delayed recognition. From the qualitative point of view, AD patients showed a severe disruption of the components of the serial position curve (primacy and central effects) reflecting the operations of the long-term memory system and a relative preservation of the component (recency effect) reflecting the functioning of the short-term memory system. Patients with MID, on the other hand, scored at a level of performance similar to that attained by normal controls in the first items of the curve, but then fell to a level similar to that shown by AD patients in the central and last components of the curve. This finding was interpreted as reflecting a decreased efficiency of the long-term memory system (and a correlative quick exhaustion of the attentional resources) of these patients. In the delayed recognition task, AD patients obtained a high number of false positive errors, showing a marked difficulty in differentiating the memorandum from other kinds of similar, previously learned, material.