In addition to the shrinkage of neurons, starting in middle age the brain begins producing smaller quantities of many neurotransmitters -- chemical messengers that relay information between nerve cells. Brain blood flow is also reduced 15-20% between age 30 and age 70, although the shrinkage of neurons may account for the reduced flow because less tissue requires less blood.
Although memory function may decline with age, emotional stability increases, according to a study reported in the Journal of Neuroscience (Volume 26, page 6422). Forget the myth that older people are crankier than younger ones. In fact, the reverse is true: Age brings increased emotional equanimity.
Australian researchers evaluated 142 people between the ages of 12 and 79. All were in good physical health and had no current or past history of mental illness. The study participants were asked to complete a questionnaire that assesses emotional stability, with higher scores suggesting more positive emotions.
In addition, the individuals' brain activity was assessed by functional magnetic resonance imaging (fMRI) while they viewed images of various facial expressions. Scores on the questionnaire kept in step with age, rising along with seniority. The brain fMRI images revealed that the older adults' emotional reactions were primarily influenced by the medial prefrontal cortex, an area of the brain needed for conscious thought.
In contrast, the emotional reactions of younger people were centered in the amygdala, a part of the brain implicated in automatic fear responses. This reorganization of the brain's emotion system may happen as older people integrate their accumulated life experience and find meaning and patterns in that experience.
Take away: The study provides a reminder that persistently negative moods in older people are not a normal part of aging.