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Cognitive
Reserve:
January 10, 2006
Subject:
How fast our minds fade with age depends how much brain power we start
with or how much we were able to build up during our prime.
Our
mental abilities peak around age 25. We won't discuss how long ago that
was for some of us. From then on the speed at which we process information,
store new memories, reason or process spatial data slowly but surely slows.
The smarter you are to begin with the more slowly this becomes a problem.
If you start out with more in reserve, it takes longer to run out. This
might sound obvious, but it's only recently that this hypothesis of ‘cognitive
reserve' has been accepted by researchers.
The
first evidence was Yaakov Stern's work. Stern measured the blood flow
in Alzheimer patients. Grouping patients by severity of outward symptoms,
he found that the higher the level of education the more severe the actual
brain damage was. This suggested some kind of ‘padding' which shielded
more educated patients from the looking as bad as would be expected from
the physical condition of their brains. [i]
Stern's more recent work says that beyond education, how mentally
engaged a person is makes a difference. [ii]
The studies have piled up supporting the cognitive reserve hypothesis.
Better-educated people suffer less cognitive impairment for a given level
of brain damage. Highly educated people are also less likely to experience
a pronounced dip in IQ after a head injury.
Once
people with high IQ, good education or occupational achievement are diagnosed
with dementia, they tend to go downhill particularly fast. For example,
well educated people with Alzheimer's disease seem to die sooner after
diagnosis than people without good education.
This
makes sense. It's not that people with high education and with Alzheimer's
disease deteriorate faster. What is happening is that by the time symptoms
appear, these people are at a relatively late stage of the disease. If
you measure the physical progress of the disease, they are already far
gone when diagnosed. As long as they have cognitive reserve in the bank,
outward signs are not apparent. Yet the disease progresses regardless,
and once that extra cushioning goes, the outward decline is dramatic.
Building
cognitive reserve is a lifetime enterprise, and the earlier we start the
better off we are. Social class, occupation and education at age 26 have
been shown to shape cognitive ability at age 53. The more education, the
more cognitive reserve a person has later in life. What you start with
still matters. The best predictor of cognitive ability in middle age is
your IQ score at age 8. People who work at complex occupations are also
somewhat protected against the risk of dementia and Alzheimer's disease.
Although
scientists are using big terms here, it's simply a matter of use it or
lose it. Using your brain, continuing education, engaging work, stimulating
thought, all appear to help maintain function. I'm waiting for the definitive
study on the effect of TV, but I think we can guess. One does wonder about
video games though.
Perhaps
I shouldn't have let my subscription to the New York Times lapse.
Animal
studies and some small scale human trials suggest there may be some things
we can do to both develop and preserve this cognitive reserve:
1.
Stay Alert: Mental activity builds up reserves of brain cells
and connections which protect against age-related decline.
2.
Keep Fit: Exercise keeps the blood flowing to the brain and
may trigger the birth of new brain cells. Fitness strengthens the brain's
executive function and preserves both white and grey matter.
3.
Minimize Stress: Anxiety prone people appear to have a faster
rate of cognitive decline. Of course if your brain was slipping away
on you, wouldn't you be feeling some anxiety?
4.
Eat Right: A diet high in mono and polyunsturated acids (fish
and olive oils), vitamin E, polyphenols and antioxidants may slow decline.
5.
Stay Sober: Smoking, alcohol and street drugs all fry brain
cells.
[i]
Inverse relationship between education and parietotemporal perfusion
deficit in Alzheimer's disease.
Stern
Y , Alexander
GE , Prohovnik
I , Mayeux
R .
Department of Neurology, Columbia University , College of Physicians and
Surgeons, New York , NY .
A higher prevalence of dementia in individuals with fewer years of education
has suggested that education may protect against Alzheimer's disease (AD).
We tested whether individuals with more years of education have a more
advanced AD before it is clinically evident. As a measure of pathophysiological
severity, we quantified regional cerebral blood flow (rCBF), by the 133Xenon
inhalation technique; a specific pattern of flow reduction in the parietotemporal
cortex corresponds to AD pathology. In 3 groups of patients with probable
AD, matched for clinical measures of dementia severity but with varying
levels of education, whole-cortex mean flows were comparable. However,
the parietotemporal perfusion deficit was significantly greater in the
group with the highest level of education, indicating that AD was more
advanced in this group. We conclude that education or its covariates or
both may provide a reserve that compensates for the neuropathological
changes of AD and delays the onset of its clinical manifestations.
PMID: 1416806 [PubMed - indexed for MEDLINE]
[ii]
Association
of life activities with cerebral blood flow in Alzheimer disease: implications
for the cognitive reserve hypothesis.
Scarmeas
N , Zarahn
E , Anderson
KE , Habeck
CG , Hilton
J , Flynn
J , Marder
KS , Bell
KL , Sackeim
HA , Van
Heertum RL , Moeller
JR , Stern
Y .
Cognitive Neuroscience Division of the Taub Institute for Research in
Alzheimer's Disease and the Aging Brain, College of Physicians and Surgeons
of Columbia University, New York, NY 10032, USA. ns257@columbia.edu
BACKGROUND: Regional cerebral blood flow (CBF), a good indirect index
of cerebral pathologic changes in Alzheimer disease (AD), is more severely
reduced in patients with higher educational attainment and IQ when controlling
for clinical severity. This has been interpreted as suggesting that cognitive
reserve allows these patients to cope better with the pathologic changes
in AD. OBJECTIVE: To evaluate whether premorbid engagement in various
activities may also provide cognitive reserve. DESIGN: We evaluated intellectual,
social, and physical activities in 9 patients with early AD and 16 healthy
elderly controls who underwent brain H(2)(15)O positron emission tomography.
In voxelwise multiple regression analyses that controlled for age and
clinical severity, we investigated the association between education,
estimated premorbid IQ, and activities, and CBF. RESULTS: In accordance
with previous findings, we replicated an inverse association between education
and CBF and IQ and CBF in patients with AD. In addition, there was a negative
correlation between previous reported activity score and CBF in patients
with AD. When both education and IQ were added as covariates in the same
model, a higher activity score was still associated with more prominent
CBF deficits. No significant associations were detected in the controls.
CONCLUSIONS: At any given level of clinical disease severity, there is
a greater degree of brain pathologic involvement in patients with AD who
have more engagement in activities, even when education and IQ are taken
into account. This may suggest that interindividual differences in lifestyle
may affect cognitive reserve by partially mediating the relationship between
brain damage and the clinical manifestation of AD.
PMID: 12633147 [PubMed - indexed for MEDLINE]
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