Studies have found that emotionally evocative stimuli are better remembered than neutral stimuli, an effect called “emotional enhancement”. Researchers have also found that the elderly experience an overall decline in memory relative to the young. We hypothesized that the elderly may experience diminished emotional enhancement, and that this may be one factor contributing to overall memory decline in the elderly. We tested elderly and young subjects on tasks of emotional memory for words and faces. In both the elderly and young, a shift in memory favoring positive stimuli (as opposed to negative and neutral stimuli) was evident, this effect being slightly more marked in the elderly. We suggest that the effects seen in both groups may be due to a shift from the amygdala-hippocampal system to the prefrontal cortex over time. We suggest that the more marked response in the elderly may be due to age-related changes in these brain systems, causing a further shift towards memory for positive material.
A decline in memory is a hallmark of aging [15], [16], [41] and [44]. The exact mechanisms of this decline are not known. However, in both animals and humans the emotional content of information can significantly influence the likelihood that it is remembered (animal studies: e.g., [14] and [48]; human studies: e.g., [16], [25], [26], [41] and [51]. Emotionally evocative information is more likely to be recalled than emotionally neutral information. We refer to this effect as emotional enhancement. Both the level of stimulus-induced arousal and the valence of stimuli (negative versus positive) may play a role in the enhancement of memory. Loss of emotional enhancement with aging could be one mechanism that limits memory in the elderly. Lifestyle changes [12], [13], [21], [36] and [51], sensory deficits [35], [38] and [46] and atrophy of brain systems responsible for memory [52], [53] and [57] all might affect the way individuals perceive and remember emotional information. The present study examines whether age affects perception and memory for emotional information that varies on the basis of valence.
Recent studies have isolated some of the brain systems involved in memory for emotional information (for review, see [34]). For instance, human imaging studies [3], [11], [26], [28] and [40] and studies of amygdala damage in both human [1], [6], [32] and [33] and animal models [2], [39] and [59] have shown that the amygdala contributes to emotion discrimination and emotional memory. Additionally, studies have shown that frontal regions may be important for the perception of emotional stimuli (e.g., [37]). This is particularly true in the elderly, who show greater frontal activation than their younger counterparts in tasks of emotion discrimination [22].
The prefrontal cortex [45] and [47], amygdala [31], [49] and [57] and hippocampus [29] and [50], show atrophy even in apparently cognitively intact healthy elderly. We asked participants to complete tasks similar to those used in studies of these neural systems in order to study emotional enhancement in both elderly and young adults. Assuming age-related atrophic changes diminish the emotional enhancement effect in the elderly, we expected to see differences between the elderly and the young on emotional memory tasks.
Emotional stimuli can be from any modality and of many stimulus types (auditory, visual, faces, words, pictures, stories). Whether all would be equally affected by aging is unknown. As an initial probe of the breadth of age effects, we examined two different kinds of stimuli (faces and words). Both of these kinds of stimuli have been shown to elicit activation in the frontal regions of the brain, the amygdala and the hippocampus during perception or memory tasks (words: [5], [9], [23], [54] and [55] faces: [10], [17], [23], [24], [60] and [61].
Thus, in this study, we look at the impact of age on both the perception of emotional stimuli and the emotional enhancement of memory. We expected that the elderly would show a loss of emotional enhancement as compared to the young.
