Impaired emotional memory enhancement on recognition of pictorial stimuli in Alzheimer's disease: no influence of the nature of encoding

Abstract

Objectives: There is some discrepancy in the results regarding emotional enhancement of memory (EEM) in Alzheimer's disease (AD). Some studies report better retrieval of emotional information, especially positive, than neutral information. This observation is similar to the positivity effect reported in healthy older adults. It was suggested that this effect is due to privileged, deeper and more controlled processing of positive information. One way of testing this is to control both the intention to encode the information and the cognitive resources involved during encoding. Studies investigating EEM in AD patients did not systematically control the nature of encoding. Consequently, the purpose of our study was to examine EEM in AD while manipulating the nature of encoding.

Methods: Two experiments were conducted. In Experiment 1 the intention to encode stimuli was manipulated by giving or not giving instructions to participants about the subsequent retrieval. In Experiment 2 cognitive resources involved during encoding were varied (low vs high). In both experiments participants performed immediate recognition task of negative, positive and neutral pictures. 41 mild AD patients and 44 older healthy adults participated in Exp. 1, and 17 mild AD patients and 20 older healthy adults participated in Exp. 2.

Results: AD patients did not present EEM. Positivity effect, better performance for positive than neutral and negative pictures was observed with older healthy adults.

Conclusion: The data suggest that EEM is disturbed in mild AD patients, with respect to both negative and positive stimuli, at least concerning laboratory, not real-life material. They also suggest there is a positivity effect in healthy older adults and lend support to the idea that this effect is due to preferential cognitive processing of positive information in this population.

Keywords: Emotional memory enhancement; Encoding conditions (intentional vs incidental, low vs high resources); Healthy older adults; Mild AD patients; Positivity effect.