The study of aging

Aging and dementia

Aging and dementia are very closely related, but few people are aware of the different types of dementia and what they actually mean in the aging process.

Normal Aging of the Brain – Types of Aging and Dementia

As we advance in age, the brain suffers cellular aging, because of incremental damage to cellular organelles and chromatin, as well as the aging and decrement of function of other organ systems.

According to studies of neuron loss in different cell groups in the brain, there is normally a slow loss of cells as we age, and a compensatory extension and increase in the complexity of the branching of remaining neurons. As a result, we lose the plasticity of brain responsiveness with aging.

Senile Dementia

Along with this picture of normal aging, there can be a more rapid and serious loss of cognitive function. When the loss is acute or sub-acute, it is because of a metabolic encephalopathy, such as an electrolyte abnormality or hepatic failure, or drug toxicity.

When the loss of function is broken down into one or more discrete episodes, it is most likely due to multiple cerebral infarcts, which is still a common cause of dementia – roughly 15 – 20 percent of all cases.

On the other hand, as we have learned to control the risk factors for stroke, especially diabetes and blood pressure, and to treat various metabolic disorders, the latter half of this century has seen an emergence of elderly people who lose mental function slowly, progressively and inexorably over a period of months to years.

There are only a few medical conditions that manifest in this way, such as thyroid disease, vitamin B1 or B12 deficiency, hydrocephalus, subdural hematomas, or rarely syphilis or another cause of chronic meningitis or encephalitis.

The workup of a patient with dementia largely consists of eliminating such potentially treatable disorders. Once these conditions have been treated, the remaining group of the demented elderly are found to have a degenerative neurological cause.

Degenerative Dementia

The best known aging disease of the degenerative causes of dementia is Alzheimer’s disease, which accounts for roughly 80 – 90 of this group. Alzheimer’s disease is a huge problem, both mentally and economically.

It affects about 5 percent of those aged 65 to 70, and increases in percentage with increasing age. About 20 percent of people over 80 were affected, with a lifetime occurrence of 40 percent of individuals who live to this age range.

The damage to the brain in Alzheimer’s disease is caused by the deposition of two types of pathological changes in the brain. First, there is the deposition of ß-amyloid protein which forms extracurricular plaques and causes local tissue injury. Still, many normal elderly individuals have great ß-amyloid protein burdens, but with very little change in mental function.

On the other hand, ß-amyloid protein seems to induce a second pathological change – neurofibrillary degeneration. The reason why neurofibrillary pathology develops in some individuals with ß-amyloid protein deposition, and not in others, is still unknown. The affected neurons, however, accumulate fibrils which are composed of paired, helical filaments. In turn, the paired, helical filaments are composed of a hyper-phosphorylated form of the tau protein.

Due to recent research, our understanding of the boundary between normal aging and dementia has advanced. Researchers have found illuminating changes associated with both normal and abnormal aging, and have also identified a group of individuals whose cognitive deficits place them in an intermediate position on the continuum between normal aging and dementia. Remarkable variability across individuals and domains of functioning has greatly complicated the study of the continuum.

Normal Aging & Dementia

Aging is characterized by both decremental and incremental changes, therefore the range and standard deviation for nearly any variable of interest increase with age. Studies of neurogenesis have provided evidence indicating regenerative potential in the adult human brain.

In order to characterize the cognitive profiles associated with normal aging and various types of abnormal aging, a common terminology is necessary.

Normal aging has been defined as the typical changes in behavior that occur with age. The general conception has accepted that subtle declines in cognition occur as part of the normal aging process. Several studies, however, have included individuals with other age-related conditions, such as cardiovascular disease or diabetes, which can affect cognition.

In normal aging, a number of skills and abilities will remain intact, or will be only slightly different. You will continue to independently handle your daily activities, such as bathing, dressing, driving and working.

Though you may notice some memory loss, you will be able to give details regarding those incidents or forgetfulness and you will be more concerned about this memory loss than your close family members. A lot of centers for healthy aging offer and give you support in using healthy aging programs.

Despite these occasional lapses, your memory for recent events and conversations will not be impaired. You may notice occasional difficulty in finding the right word, but your vocabulary will remain rich nonetheless. You may still be able to operate your common household appliances as you age, but unwilling to learn how to operate new devices.

Age-Associated Memory Impairment (AAMI)

The term age-associated memory impairment was introduced in 1986 by a National Institute of Mental Health work group to define what was previously referred to as “benign forgetfulness”.

The original concept of benign forgetfulness was defined without formal psychometric testing and criteria, it entailed that some gradual cognitive change with age is normal. The formal criteria developed by the 1986 work group included:

  1. age 50 or older
  2. subjective decline or loss in memory function
  3. performance at least one standard deviation
  4. preserved intellectual ability
  5. failure to meet the criteria for depression
  6. failure to meet the criteria for dementia

Age-Associated Cognitive Decline (AACD)

This term has been used to describe a group of older adults in which multiple domains of cognition were mildly compromised compared to younger individuals. As in the case for AAMI, using younger adults as a reference group for AACD means that many older individuals will be classified as having AACD, yielding little predictive or discriminative value to the classification.

Mild Cognitive Impairment (MCI)

MCI has been used to describe the group of older individuals who have memory problems that are greater than expected for their age, but do not meet the criteria for dementia. Unlike AAMI and AACD, the reference group for a MCI diagnosis is composed of age-matched peers. Mild cognitive impairment typically presents with subjective memory difficulties of insidious offset. Subjective cognitive complaints can actually be a harbinger of dementia even before the development of demonstrable cognitive deficits, especially in highly educated individuals.