As we grow older, we experience a number of cognitive changes, such as poorer working memory, declining ability to encode new memories, and slower processing speeds. By contrast, a number of critical abilities (short-term memory, autobiographical memory, semantic knowledge) remain stable. One of the major avenues of research for the cognitive neuroscience of aging explores how these behavioral changes correlate with changes in neural structure and function. Such studies, which rely heavily on neuroimaging techniques, have revealed that older adults have lower volumes of grey matter than do younger adults, primarily as a result of decreased synaptic density (i.e. the number of connections ("synapses") between neurons). Particularly affected are the prefrontal cortex (PFC), highly involved in processing speed, attention, and working memory, and medial temporal structures such as the hippocampus, which is involved in encoding information into episodic memories.
One ability which is not believed to decline with age is emotional processing. In fact, recent behavioral studies suggest that healthy older adults may actually perform better on tasks involving the processing of emotional stimuli than younger adults, and tend to have an enhanced experience of positive emotions and/or reduced experiences of negative emotions. To date, however, little is known of the structural and functional integrity of the neural regions associated with emotional processing, such as the anterior cingulate cortex (ACC, located in the middle of the brain right behind the PFC, may be important for one's conscious subjective emotional awareness), insula (important for "bodily" experiences of emotion, e.g. heart rate, breathing), and ventral striatum (involved in motivation and goal-directed positive emotion). How is the activation of these regions during emotional processing affected by age?
To understand the biology of such age-associated changes, Brian Knutson and Laura Carstensen at Stanford used fMRI to examine brain activity during emotional "incentive processing" tasks (i.e. anticipation of a loss or gain) in younger (19-27) and older (65-81) adults, and recently published their results online in Nature Neuroscience.
Participants viewed one of six cues, which displayed the amount of money that could be gained or lost on a certain trial (+$0, +$0.50, +$5.00, or - the same amounts). They were then presented with a target, and if they responded quickly enough they either gained or avoided losing the specified amount. Both age groups performed equivalently, earning similar amounts.
According to data reported by the participants, both younger and older adults felt similarly in anticipation of gaining money, but younger adults responded more strongly in response to anticipation of monetary loss. In other words, the older adults experiences less negative emotion in response to the same cues. This difference has been previously observed, but it may have been due to a bias in self-reports; thus, the researchers used fMRI to look for neural correlates of these behavioral differences.
They found that during reward anticipation (after participants saw the cue, but before they responded to the target), both younger and older adults showed equal levels of activation of the ventral striatum, anterior insula, and medial caudate (part of the dorsal striatum). During loss anticipation, however, younger adults had greater activation of the medial caudate and anterior insula than their elders. Thus, both affective and neural data indicate that older adults experience diminished negative emotions in response to loss anticipation, but retain their abilities to respond positively to reward anticipation. The asymmetry with which age affects the functioning of these regions is intriguing; clearly, they are still capable of normal levels of activation, but are somehow dampened during certain negative emotions.
The authors comment that the "age-related sparing of positive emotional experience may be related to efforts to optimize emotional experiences as one approaches the end of life. One aspect of this optimization may involve reducing negative arousal during anticipation of negative events." This sounds quite rosy to me, but the authors also mention that reduced emotional reactions to anticipated loss may have negative effects. Older people may have, for example, altered abilities of risk assessment, which may lead to sub-optimal decision making. Nevertheless, the overall enhancement of well-being may be worth the risk.
Reference: Larkin GRS, Gibbs SEB, Khanna K, Nielsen L, Carstensen LL, Knutson B. (2007). Anticipation of monetary gain but not loss in healthy older adults. Nature Neuroscience Apr 29; [Epub ahead of print]