Physical changes

With age, the brain undergoes predictable physical changes:

• Contrary to previous belief, the number of neurons does not decline significantly throughout the brain over time. Very little neuron loss occurs in the hippocampus, the region most essential for normal memory.
  
  
• Some large individual neurons do appear to shrink somewhat. Certain parts of neurons, including some dendrites and myelin, may also be lost with age.
  
  
• Structural and functional changes may occur in synapses, the tiny channels through which brain cells send chemical messages to one another.
  
  
• There is some decrease in brain volume.
  
  
• In advanced age, almost all brains develop certain protein accumulations. These structures include neurofibrillary tangles – which contain abnormal forms of the protein tau – and deposits of the protein fragment beta-amyloid.
  
  
  
  • Individuals who develop dementia tend to show more such abnormalities than those with no impairment.
    
    
  • On autopsy, some individuals with no record of significant dementia prior to death will show enough toxic tau and beta-amyloid to meet the neuropathological criteria for Alzheimer’s.

Functional changes

In general, functional changes associated with aging are less well understood than are physical changes. Nonetheless, scientists generally agree that:

• Beginning in their late 50s, many individuals report some slowing in their ability to learn or retrieve information. However, research suggests that optimally functioning older adults can learn and remember as well as their younger counterparts when they work at their own pace.
  
  
• Among different age groups, average performance on functional tests tends to be lower for older groups than for younger ones.
  
  
• The range of individual performance overlaps significantly for all age groups.
  
  
• For older adults, individual performance varies around the average more than it does for younger adults.
  
  
• Vocabulary tends to continue increasing until people reach their 80s.
  
  
• The attempt to compare performance among different age groups may be complicated by the “cohort effect.” Distinctions in performance may not be due to age, but to prevailing conditions that affected an entire generation and have since changed. Such conditions can involve general nutrition, educational attainment and access to health care.

Alzheimer’s disease and middle age

Although Alzheimer’s is chiefly a disease of older adults, it can occur in individuals as young as their 40s and 50s. Most middle-aged adults with Alzheimer’s tend to develop the common form of the disease that is not directly linked to genes. Yet many of these people report significant difficulty in obtaining a diagnosis.

If middle-aged patients express persistent concern about cognitive function, they should receive preliminary cognitive testing. Moreover, a physician might want to get the patient’s permission to ask family members whether they have noticed problems with the patient’s cognitive abilities.

For a detailed discussion of this issue, please see our report: Early Onset Dementia: A National Challenge, A Future Crisis