Janis Thereault, M.D.
Associate Professor
Department of Anesthesiology, UC Irvine
Janis.thereault@med.va.gov
Aging and age-related disease are not the same.
Those manifestations that are universally present in all elderly
individuals and that increase in magnitude with advancing age,
represent aging.
Structure and Function
Effects of aging on the nervous system include:
- selective attrition of cerebral and cerebellar cortical
neurons
- neuron loss within certain areas of the thalamus, locus
ceruleus, and basal ganglia
- general reduction in neuron density, with loss of 30 percent
of brain mass by age 80
- decreased numbers of serotonin receptors in the cortex
- reduced levels of acetylcholine and acetylcholine receptors
in several regions of the brain
- decreased levels of dopamine in the neostriatum and substantia
nigra and reduced numbers of dopamine receptors in the neostriatum.
The association of serotonergic, cholinergic and dopaminergic
systems, respectively with mood, memory, and motor function,
may partially account for depression, loss of memory and motor
dysfunction in the elderly.
Afferentation
There is also a generalized reduction in afferentation, evident
as progressively increased thresholds for virtually all forms
of perception, including vision, hearing, touch, joint position
sense, smell and peripheral pain and temperature.
Sleep
Normal physiologic changes in sleep occur with advancing age,
with probably the most common change being a decline in slow-wave,
or delta, sleep. Delta sleep is thought to be the deepest level
of sleep and perhaps the most restoring. Increased latency to
sleep onset is often present, as well as increased awakenings
and periods of wakefulness during the night. Simultaneous with
this increasing wakefulness at night is an increasing tendency
for sleeping and sleepiness during the day. The timing of natural
sleeping/waking cycles probably changes with age. In general,
the usual bedtimes and awakening times of the elderly tend to
occur earlier and are referred to as "sleep phase advancing".
Two sleep disorders, sleep-disordered breathing (SDB) and periodic
limb movements in sleep (PLMS), are commonly seen in the elderly.
Memory
Memory and reasoning performance decline linearly with advancing
age. Age-related decline in frontostriatal function, as supported
by neuroimaging studies, most likely accounts for the majority
of normal age-related decline in memory performance.
Plasticity
Experience is the major stimulant of brain plasticity, which
is the brainās ability to change structure and function. It
is thought that an increase in dendritic growth and number of
synapses with aging helps to compensate for the loss of neurons.
Age-related Diseases
Age-related diseases such as cerebral arteriosclerosis, Alzheimerās
and Parkinsonās disease are all more common with advancing age.
Most strokes affect those older than 70 years and the risk doubles
every 10 years after age 55. The prevalence rates for dementia
and Alzheimerās disease double approximately every five years
from rates of 2 to 3 percent in the age category of 65 to 75
years to more than 30 percent in persons age 85 and older. Onset
of symptoms in Parkinsonās disease usually occurs between ages
60 and 69, although in 5 percent of patients the first signs
are seen prior to age 40. About 1 percent of persons age 65
and older and 2.5 percent of those older than age 80 have Parkinsonās
disease.
Bibliography:
Muravchick S. The physiologic and pharmacologic implications
of aging. 37th Annual Refresher Course Lectures
and Clinical Update Program. American Society of Anesthesiologists.1986;
No. 275.
The Aging Brain. Geriatrics. 1998; 53.
Hendrie HC. Epidemiology of alzheimerās disease. Geriatrics.
1997; 52:S4-S8.
Uitti RJ. Tremor: How to determine if the patient has parkinsonās
disease. Geriatrics. 1998; 53:30-36.