MODULE SUPPLEMENT: NEUROLOGICAL SYSTEM
Cerebral Blood Flow and Cerebral Metabolism

Blood flow is connected to functional activity, and thus cerebral blood flow is generally proportional to cerebral metabolic rates for oxygen and for glucose. Both cerebral blood flow and cerebral metabolism are noted to decline with aging (Mattson, 1999), which may relate to the brain's loss of cells and mass. Earlier work by Meyer and his colleagues (1993) suggested that regional changes in blood flow were more evident in gray matter rather than white and that the decrease occurred even in the absence of risk factors for stroke or other neurological deficits. However, data also suggest that sustained physical activity after the age of 65 helped to maintain both blood flow and cognitive status (Mattson, 1999; Meyer, et al., 1993), a theme that is prominent throughout the literature on aging. Further, there remains a range of individual variability in the extent of changes seen.

In contrast to what is commonly seen with aging, cerebral metabolism is significantly altered in Alzheimer's type dementia. (See Unraveling the Mystery: The Changing Brain in AD--Alzheimer's Disease Education & Referral Center for a comparison of normal vs. abnormal metabolism as defined by a PET scan--NOTE: This link will open in a new browser window which you can close to return here.)

Does the change in blood flow matter?

The brain is highly dependent on blood flow and a consistent supply of oxygen and glucose to maintain neuronal function. Any decrease can cause neuronal malfunction. Older adults tend to be vulnerable to cognitive dysfunction secondary to many causes, ranging from decreased blood pressure to infections. Thus, any acute change in cognitive functioning needs to be assessed for an underlying cause.