Summary Functional Neuroimaging Studies

Studies of resting brain function indicate that there are small reductions in both glucose metabolism and cerebral blood flow with age and an age-related reduction of nigrostriatal dopamine function. The declines in global measurements occur within the average range of 10-20% after age 60. Regional metabolism and blood flow also decrease with age. Changes have been observed most commonly in frontal, temporal, and parietal lobes of the brain. Of these regions, the frontal lobes appear to exhibit the greatest decline when assessed with either glucose or blood flow techniques.

Brain function during activation also demonstrates age-related changes. Studies of visual function show activation differences in occipital, temporal, and frontal regions. Generally, these differences are seen as decreases in activation of visual areas within the occipital and temporal lobes and increases in activation of areas in the frontal cortex. Although individual studies of memory function yield slightly different results, the similarities suggest that there is a reorganization of brain activation patterns in the elderly during memory tasks. This reorganization can been seen during tasks involving both encoding and retrieval of visual and verbal information. Some differences are observed in occipital and parietal lobes of the brain, but the most prominent age-associated differences are seen in frontal lobe activation, especially involving prefrontal cortical regions. These frontal lobe differences include increased activation as well as involvement of regions unlike that observed in young subjects. Often, in tasks in which frontal activation is predominant in one hemisphere in young subjects, the activation becomes bilateral in the elderly. Together, the activation data suggest that decreases in cortical function and subsequent recruitment of novel regions during task performance may represent some form of functional compensation in the aging brain, although perhaps not sufficient to maintain performance at the same levels of accuracy and speed as in young subjects.

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