Wednesday, July 05, 2006

The Mellow Years?: Neural Basis of Improving Emotional Stability over Age

Several studies have documented that older adults show a shift in the ratio of positive-to-negative emotion, with a reduction in the experience, memory, and recognition of negative emotion, but an increase for positive emotion. A recent article by Williams et al with the title of this post shows some of what is going on in in the brains of these older adults. They used fMRI (function Magnetic Resonance Imaging) or ERP (Event related potentials recorded on the surface of the scalp) to examine the activity of the medial prefrontal cortex (MPFC) that is central in inhibiting or enhancing emotional functions. Subject also rated their own reactions to photographs shown during the measurements of fearful, happy, or neural faces. A shift in responses to positive versus negative emotion over age was seen in both recognition and brain function. Recognition of negative emotion (fear, shown in red in right part of figure) showed a significant decline as a function of increasing age, whereas
recognition for positive emotion (happiness) increased.

Credit: J. Neuroscience

Changes in both ERP (over the time course 40–450 ms after stimulus) and fMRI measures over age. Happiness relative to neutral showed a decrease in activity over the medial prefrontal region (shown in blue), which was most apparent for neural activity elicited during the early phase of processing (40–150 ms after stimulus). In response to fear, in contrast, there was an increase in activity over the medial prefrontal cortex with age (shown in red), which ERPs showed was most apparent for neural activity occurring in the later phase of the time course (180–450 ms after stimulus).

Fear elicited corresponding increases in medial prefrontal activation, apparent during the later (180–450 ms) controlled phase of processing. In contrast, medial prefrontal activation to happiness attenuated over age, apparent in the early, automatic (within 150 ms) phase of the time course. These changes indicate that processing resources are shifted from the automatic phase of stimulus appraisal toward a greater allocation during the controlled phase of stimulus evaluation. The authors propose that this shift in resources supports better selective control of reactions to negative, particularly threat-related stimulation and allows positive responses to proceed without restraint. Their observation that this shift in processing of negative versus positive emotion predicted better emotional wellbeing with older age supports the view that it contributes to an increasingly adaptive regulation of emotion.

The authors propose that life experience and changing motivational goals may drive plasticity in the medial prefrontal brain systems to increase selective control over the balance of negative and positive emotion, with the consequence of improving emotional wellbeing.

"The motivation to achieve better emotional control in older adults may come from the increasing awareness of one’s mortality and the desire to maximize the meaningfulness of environmental events and input, over and above the need for acquisition. With repeated emotional experiences over the lifespan, humans may learn to be more selective about which input is likely to provide quality positive outcomes as opposed to cause distress. Consistent with this view, older adults are more selective about their social activities and tend to prioritize quality rather than quantity."

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