Processes of Age-Related Neurological Decline

(Merck Manual of Geriatrics)

Loss of nerve cells: "With normal aging, the number of nerve cells in the brain decreases. Cell loss is minimal in some areas (eg, brain stem nuclei, supraoptic and paraventricular nuclei) but is as great as 10 to 60% in others (eg, hippocampus). Loss also varies within the cortex (e.g., loss is 55% in the superior temporal gyrus but 10 to 35% in the tip of the temporal lobe). From age 20 or 30 to age 90, brain weight declines about 10%, and the area of the cerebral ventricles relative to the entire brain (as seen on cross section in the coronal view) may increase three to four times. The clinical effects of these changes are difficult to determine because brain weight and ventricular size may not correlate with intelligence; indeed, severe dementia may occur in persons who have normal ventricular size for their age." Regeneration of New Brain Cells is possible. For many years, scientists believed that a brain only had so many cells and once those were lost, that was it. Not so. See recent studies since 1999.

Accumulation of free radicals: "Free radicals (atoms or molecules with one unpaired electron), which are produced normally during metabolism, accumulate with age and may have a toxic effect on certain nerve cells."

Changes in neurotransmitter systems: "With normal aging, changes in neurotransmitter systems (enzymes, receptors, and neurotransmitters) occur (Age Related Changes in Neurotransmitter Systems). For example, choline O- acetyltransferase levels tend to decrease; the number of cholinergic receptors tends to decrease; and g-aminobutyric acid, serotonin, and catecholamine levels usually decrease. Choline O-acetyltransferase levels and dopamine levels may further decrease in Alzheimer's disease and in Parkinson's disease, respectively. Another age-related change is an increase in monoamine oxidase levels. When this increase is inhibited by monoamine oxidase inhibitors, onset of disability in patients with Parkinson's disease may be forestalled."

Decreased cerebral blood flow: "With normal aging, cerebral blood flow decreases by about 20% on average; decreases are even greater in persons with small-vessel cerebrovascular disease due to diabetes and hypertension. Although blood flow in women is usually greater than in men until age 60, the subsequent rate of decrease is slightly more rapid. Decreases are greater in certain areas of the brain (eg, the prefrontal region) and are greater in gray matter than in white matter."

Compensatory mechanisms: "Certain properties of the brain may reduce the clinical effects of age-related changes. Redundancy is a property whereby more nerve cells exist than are needed. For example, diabetes insipidus (due to a lack of antidiuretic hormone) does not appear until > 85% of the nerve cells in the supraoptic and paraventricular nuclei have been destroyed. Furthermore, hydrocephalic patients, who have only a thin cerebral cortical mantle, may have normal intelligence. The number of cells required for certain functions is unknown, so the extent of redundancy is difficult to estimate. However, redundancy probably reduces the effects of age-related neuron loss."

Plasticity at the nerve cell level involves compensatory lengthening and production of dendrites in remaining nerve cells to offset the age-related gradual deterioration and loss of nerve cells. New connections in the dendritic tree may compensate for the fewer nerve cells. Plasticity in the dendritic tree may also occur in Alzheimer's disease, perhaps as a biologic attempt to preserve function.

Consider this:

  • More than 30% of prison inmates are there because of behavior induced by neurological deficit and dysfunction, combined with poor socioeconomic conditions, that were never remedied or addressed in their lives.

  • Our society not only suffers from a dysfunctional, non brain-centered educational system, but so many people suffer from neurological impairment due to poor diet and an environment filled with neurotoxins.