Aging - rate of cognitive decline

White matter appears to decrease faster than grey matter, but doesn't begin to decline until the forties. Presumably this relates to the decline in processing speed that is the most evident characteristic of age-related decline.

Grey matter, on the other hand, declines at a fairly constant rate from adolescence, mirroring a decline in processing ability that seems to start as early as the twenties.

Cognitive decline seems to be faster in women than men. This presumably reflects apparent gender differences in brain activity. For example, while women seem to have a greater density of brain cells in the prefrontal cortex, they also show a steeper rate of decline so that, in old age, the density is similar between the genders.

There is some evidence that individual differences in processing speed and memory are more important than age, and that personality attributes affect the rate of cognitive decline and brain atrophy.

Some gene variants, including the so-called Alzheimer’s gene, are associated with a faster rate of decline, or an earlier start. These may be triggered by activity in early adulthood. Head size in adulthood also seems to affect rate of decline. Head size in adulthood reflects not only head size at birth, but growth in the early years — pointing to the importance of providing both proper nourishment and intellectual stimulation in these early years.

Comparison of 99 chimpanzee brains ranging from 10-51 years of age with 87 human brains ranging from 22-88 years of age has revealed that, unlike the humans, chimpanzee brains showed no sign of shrinkage with age. But the answer may be simple: we live much longer. In the wild, chimps rarely live past 45, and although human brains start shrinking as early as 25 (as soon as they reach maturity, basically!), it doesn’t become significant until around 50.

The answer suggests one reason why humans are uniquely vulnerable to Alzheimer’s disease — it’s all down to our combination of large brain and long life. There are other animals that experience some cognitive impairment and brain atrophy as they age, but nothing as extreme as that found in humans (a 10-15% decline in volume over the life-span). (Elephants and whales have the same two attributes as humans — large brains and long lives — but we lack information on how their brains change with age.)

The problem may lie in the fact that our brains use so much more energy than chimps’ (being more than three times larger than theirs) and thus produce a great deal more damaging oxidation. Over a longer life-span, this accumulates until it significantly damages the brain.

If that’s true, it reinforces the value of a diet high in antioxidants.

[2500] Sherwood CC, Gordon AD, Allen JS, Phillips KA, Erwin JM, Hof PR, Hopkins WD. Aging of the cerebral cortex differs between humans and chimpanzees. Proceedings of the National Academy of Sciences [Internet]. 2011 ;108(32):13029 - 13034. Available from: http://www.pnas.org/content/108/32/13029.abstract

Reports on cognitive decline with age have, over the years, come out with two general findings: older adults do significantly worse than younger adults; older adults are just as good as younger adults. Part of the problem is that there are two different approaches to studying this, each with their own specific bias. You can keep testing the same group of people as they get older — the problem with this is that they get more and more practiced, which mitigates the effects of age. Or you can test different groups of people, comparing older with younger — but cohort differences (e.g., educational background) may disadvantage the older generations. There is also argument about when it starts. Some studies suggest we start declining in our 20s, others in our 60s.

One of my favorite cognitive aging researchers has now tried to find the true story using data from the Virginia Cognitive Aging Project involving nearly 3800 adults aged 18 to 97 tested on reasoning, spatial visualization, episodic memory, perceptual speed and vocabulary, with 1616 tested at least twice. This gave a nice pool for both cross-sectional and longitudinal comparison (retesting ranged from 1 to 8 years and averaged 2.5 years).

From this data, Salthouse has estimated the size of practice effects and found them to be as large as or larger than the annual cross-sectional differences, although they varied depending on the task and the participant’s age. In general the practice effect was greater for younger adults, possibly because younger people learn better.

Once the practice-related "bonus points" were removed, age trends were flattened, with much less positive changes occurring at younger ages, and slightly less negative changes occurring at older ages. This suggests that change in cognitive ability over an adult lifetime (ignoring the effects of experience) is smaller than we thought.

More data from the National Survey of Midlife Development in the United States has revealed that cognitive abilities reflect to a greater extent how old you feel, not how old you actually are. Of course that may be because cognitive ability contributes to a person’s wellness and energy. But it also may reflect benefits of trying to maintain a sense of youthfulness by keeping up with new trends and activities that feel invigorating.

[171] Schafer MH, Shippee TP. Age Identity, Gender, and Perceptions of Decline: Does Feeling Older Lead to Pessimistic Dispositions About Cognitive Aging?. The Journals of Gerontology Series B: Psychological Sciences and Social Sciences [Internet]. 2009 ;65B(1):91 - 96. Available from: http://psychsocgerontology.oxfordjournals.org/content/65B/1/91.abstract

An imaging study involving 79 volunteers aged 44 to 88 has found lower volumes of gray matter and faster rates of decline in the frontal and medial temporal lobes of those who ranked high in neuroticism traits, compared with those who ranked high in conscientious traits. These are brain regions particularly affected by aging. The idea that this might occur derived from the well-established effects of chronic stress on the brain. This is the first study to investigate whether the rate and extent of cognitive decline with age is influenced by personality variables. Extraversion, also investigated, had no effect. The study does not, however, rule out the possibility that it is reduction in brain tissue in these areas that is affecting personality. There is increasing evidence that people tend to become more neurotic and less conscientious in early-stage Alzheimer's.

Older news items (pre-2010) brought over from the old website

Marital status and gender affects rate of age-related cognitive decline; education doesn’t

Analysis of data from 6,476 adults born prior to 1924 (taken from the AHEAD study), who were given five rounds of cognitive testing between 1993 and 2002, has found marital status is a significant factor in rate of cognitive decline, with widows and widowers and those who never married declining faster than married individuals. This is consistent with findings of the benefits of social stimulation and support for aging cognition. Confirming earlier indications, it was also found that women declined faster than men. Level of education did not affect rate of decline. There was an effect of socioeconomic status, in that those in the bottom quintile declined more slowly than those in the highest quintile, and non-Hispanic blacks declined more slowly than non-Hispanic whites, but the chief difference was at baseline — that is, socioeconomic status and race were a far more significant factor in the level of cognitive performance at the start of the study, compared to the rate of decline with age.

[628] Karlamangla AS, Miller-Martinez D, Aneshensel CS, Seeman TE, Wight RG, Chodosh J. Trajectories of Cognitive Function in Late Life in the United States: Demographic and Socioeconomic Predictors. Am. J. Epidemiol. [Internet]. 2009 ;170(3):331 - 342. Available from: http://aje.oxfordjournals.org/cgi/content/abstract/170/3/331

http://www.eurekalert.org/pub_releases/2009-08/uoc--sfn080709.php

Evidence cognitive decline begins in late 20s

A seven-year study involving 2,000 healthy participants between the ages of 18 and 60 has revealed that in 9 of 12 tests the average age at which the top scores were achieved was 22. A notable decline in certain measures of abstract reasoning, processing speed and spatial visualization became apparent at 27. Average memory declines could be detected by about age 37. However, accumulated knowledge skills, such as improvement of vocabulary and general knowledge, actually increase at least until the age of 60. It must be remembered however that there is considerable variance from person to person.

[239] Salthouse TA. When does age-related cognitive decline begin?. Neurobiology of Aging [Internet]. 2009 ;30(4):507 - 514. Available from: http://www.neurobiologyofaging.org/article/S0197-4580(09)00021-9/abstract

http://www.eurekalert.org/pub_releases/2009-03/uov-cdb031909.php
http://news.bbc.co.uk/2/hi/health/7945569.stm

Education may not affect how fast you will lose your memory

A study involving some 6,500 older Chicago residents being interviewed 3-yearly for up to 14 years (average 6.5 years), has found that while at the beginning of the study, those with more education had better memory and thinking skills than those with less education, education was not related to how rapidly these skills declined during the course of the study. The result suggests that the benefit of more education in reducing dementia risk results simply from the difference in level of cognitive function.

[362] Wilson RS, Hebert LE, Scherr PA, Barnes LL, Mendes de Leon CF, Evans DA. Educational attainment and cognitive decline in old age. Neurology [Internet]. 2009 ;72(5):460 - 465. Available from: http://www.neurology.org/cgi/content/abstract/72/5/460

http://www.eurekalert.org/pub_releases/2009-02/aaon-emn012709.php

Brain slows at 40, starts body decline

We get slower as we age, we all know that. This slowness reflects damage to the myelin sheathing (“white matter”) that coats nerve fibers and is vital for speedy conduction of electrical impulses. A study involving 72 healthy men aged 23 to 80 has found that the speed with which they could tap an index finger, and the health of the myelin in the region that orders the finger to tap, both peaked at age 39, then gradually declined with increasing age. This explains why you don’t get many world-class athletes after 40. Luckily, it probably takes a little longer before the myelin in cognitive areas starts to fray (a decade or so, it’s thought). The finding is consistent with a recent report that the system that’s supposed to repair myelin becomes less efficient with age. More research is looking at what you can do to help your myelin, but in the meantime, it’s suggested that mental and physical activity may help stimulate myelin repair, and stress may damage it.

[468] Villablanca P, Bartzokis G, Lu PH, Tingus K, Mendez MF, Richard A, Peters DG, Oluwadara B, Barrall KA, Finn PJ. Lifespan trajectory of myelin integrity and maximum motor speed. Neurobiology of Aging [Internet]. 2008 . Available from: http://www.neurobiologyofaging.org/article/S0197-4580(08)00302-3/abstract

http://www.physorg.com/news144948216.html
http://www.eurekalert.org/pub_releases/2008-10/uoc--pdc101708.php

Memory loss becoming less common in older Americans

A new nationally representative study involving 11,000 people shows a downward trend in the rate of cognitive impairment among people aged 70 and older, from 12.2% to 8.7% between 1993 and 2002. It’s speculated that factors behind this decline may be that today’s older people are much likelier to have had more formal education, higher economic status, and better care for risk factors such as high blood pressure, high cholesterol and smoking that can jeopardize their brains. In fact the data suggest that about 40% of the decrease in cognitive impairment over the decade was likely due to the increase in education levels and personal wealth between the two groups of seniors studied at the two time points. The trend is consistent with a dramatic decline in chronic disability among older Americans over the past two decades.

[1307] Langa KM, Larson EB, Karlawish JH, Cutler DM, Kabeto MU, Kim SY, Rosen A. Trends in the Prevalence and Mortality of Cognitive Impairment in the United States: Is There Evidence of a Compression of Cognitive Morbidity?. Alzheimer's & dementia : the journal of the Alzheimer's Association. 2008 ;4(2):134 - 144.

http://www.eurekalert.org/pub_releases/2008-02/uomh-mla021808.php

People at genetic risk for Alzheimer's age mentally just like noncarriers

A long-running study involving 6,560 people has found that carriers of the so-called ‘Alzheimer’s gene’— the APOE4 allele — does not contribute to cognitive change during most of adulthood. There was no difference in cognitive performance between carriers and non-carriers prior to the development of dementia symptoms.

[1189] Jorm AF, Mather KA, Butterworth P, Anstey KJ, Christensen H, Easteal S. APOE genotype and cognitive functioning in a large age-stratified population sample. Neuropsychology [Internet]. 2007 ;21(1):1 - 8. Available from: http://www.ncbi.nlm.nih.gov/pubmed/17201525

http://www.eurekalert.org/pub_releases/2007-01/apa-pag010307.php

Longevity gene also helps retain cognitive function

The Longevity Genes Project has studied 158 people of Ashkenazi, or Eastern European Jewish, descent who were 95 years of age or older. Those who passed a common test of mental function were two to three times more likely to have a common variant of a gene associated with longevity (the CETP gene) than those who did not. When the researchers studied another 124 Ashkenazi Jews between 75 and 85 years of age, those subjects who passed the test of mental function were five times more likely to have this gene variant than their counterparts. The gene variant makes cholesterol particles in the blood larger than normal.

[916] Barzilai N, Atzmon G, Derby CA, Bauman JM, Lipton RB. A genotype of exceptional longevity is associated with preservation of cognitive function. Neurology [Internet]. 2006 ;67(12):2170 - 2175. Available from: http://www.ncbi.nlm.nih.gov/pubmed/17190939

http://tinyurl.com/yrf5s4
http://www.eurekalert.org/pub_releases/2006-12/aaon-lga121906.php

Risk of mild cognitive impairment increases with less education

A study of 3,957 people from the general population of Olmsted County, Minnesota is currently in train to find how many of those who did not have dementia might have mild cognitive impairment. A report on the findings so far suggests 9% of those aged 70 to 79 and nearly 18% of those 80 to 89 have MCI. Prevalence varied not only with age but also years of education: 25% in those with up to eight years of education, 14% in those with nine to 12 years, 9% in those with 13 to 16 years, and 8.5% in those with greater than 16 years.

Findings from this study were presented April 4 at the American Academy of Neurology meeting in San Diego.

http://www.eurekalert.org/pub_releases/2006-04/mc-mci033006.htm

Human cerebellum and cortex age in very different ways

Analysis of gene expression in five different regions of the brain's cortex has found that brain changes with aging were pronounced and consistent across the cortex, but changes in gene expression in the cerebellum were smaller and less coordinated. Researchers were surprised both by the homogeneity of aging within the cortex and by the dramatic differences between cortex and cerebellum. They also found that chimpanzees' brains age very differently from human brains; the findings cast doubt on the effectiveness of using rodents to model various types of neurodegenerative disease.

[951] Fraser HB, Khaitovich P, Plotkin JB, Pääbo S, Eisen MB. Aging and Gene Expression in the Primate Brain. PLoS Biol [Internet]. 2005 ;3(9):e274 - e274. Available from: http://dx.doi.org/10.1371/journal.pbio.0030274

http://www.eurekalert.org/pub_releases/2005-08/hu-hca072805.php

Childhood environment important in staving off cognitive decline

Confirming earlier studies, a British study of 215 men and women aged between 66 and 75, has found that the larger a person's head, the less likely their cognitive abilities are to decline in later years. Those with the smallest heads had a fivefold increased risk of suffering cognitive decline compared with those with the largest heads. Encouragingly, however, this doesn’t mean you’re doomed at birth — the researchers found that it wasn’t head circumference at birth that was important, but head size in adulthood. During the first year of life, babies' brains double in size, and by the time they are six, their brain weight has tripled. These, it appears, are the crucial years for laying down brain cells and neural connections — pointing to the importance of providing both proper nourishment and intellectual stimulation in these early years.

[1208] Gale CR, Walton S, Martyn CN. Foetal and postnatal head growth and risk of cognitive decline in old age. Brain [Internet]. 2003 ;126(10):2273 - 2278. Available from: http://brain.oxfordjournals.org/cgi/content/abstract/126/10/2273

http://observer.guardian.co.uk/uk_news/story/0,6903,1051264,00.html

Failing recall not an inevitable consequence of aging

New research suggests age-related cognitive decay may not be inevitable. Tests of 36 adults with an average age of 75 years found that about one out of four had managed to avoid memory decline. Those adults who still had high frontal lobe function had memory skills “every bit as sharp as a group of college students in their early 20s." (But note that most of those older adults who participated were highly educated – some were retired academics). The study also found that this frontal lobe decline so common in older adults is associated with an increased susceptibility to false memories – hence the difficulty often experienced by older people in recalling whether they took a scheduled dose of medication.

The research was presented on August 8 at the American Psychological Association meeting in Toronto.

http://www.eurekalert.org/pub_releases/2003-08/wuis-fmf080703.php

How aging brains compensate for cognitive decline

Many of the cognitive deficits associated with advancing age are related to functions of the prefrontal cortex such as working memory, decision-making, planning and judgment. Postmortem examination of 20 brains ranging in age from 25 to 83 years, confirm that prefrontal regions may be particularly sensitive to the effects of aging. It also appears that white matter decreases at a faster rate than grey matter with age.

Kigar, D.L., Walter, A.L., Stoner-Beresh, H.J. & Witelson, S.F. 2001. Age and volume of the human prefrontal cortex: a postmortem study. Paper presented to the annual Society for Neuroscience meeting in San Diego, US.

Memory starts to decline in our mid-twenties

Studies of more than 350 men and women between the ages of 20 and 90 have found that cognitive decline starts as early as the twenties, and this decline in cognitive processing power appears to be constant - that is, the rate of decline is the same when you are in your twenties as when you are in your sixties. However young adults don't notice this decline because the loss hasn't yet become great enough to affect everyday activities.

Denise Park, who directs the Center for Aging and Cognition at the University of Michigan Institute for Social Research (ISR) presented a paper on these studies on Aug. 24 in San Francisco at the annual meeting of the American Psychological Association.

http://www.umich.edu/~newsinfo/Releases/2001/Aug01/r081301a.html

Gray matter may decline from adolescence, but white matter keeps growing until our late forties

Brain scans of 70 men, ages 19 to 76 confirms that the brain's gray matter, the cell bodies of nerve cells, declines steadily from adolescence. But surprisingly, the white matter, the fatty material that insulates the long extending branches of the nerve cells and makes nerve signals move faster, in the frontal parts of the brain appears to grow at least until the late 40's, before beginning to decline. The growth of white matter may improve the brain's ability to process information.

[1246] Bartzokis G, Beckson M, Lu PH, Nuechterlein KH, Edwards N, Mintz J. Age-Related Changes in Frontal and Temporal Lobe Volumes in Men: A Magnetic Resonance Imaging Study. Arch Gen Psychiatry [Internet]. 2001 ;58(5):461 - 465. Available from: http://archpsyc.ama-assn.org/cgi/content/abstract/58/5/461

http://www.nytimes.com/2001/05/22/health/22VITA-3.html

Mental faculties unchanged until the mid-40s

A large-scale study of mental abilities in adults found that mental faculties were unchanged until the mid-40s, when a marked decline began and continued at a constant rate. The ability to remember words after a delay was especially affected. Accuracy did not seem to be affected, only speed.

The paper was presented to a British Psychological Society conference in London.

http://www.guardian.co.uk/Archive/Article/0,4273,4108165,00.html

Gender differences in frontal lobe neuron density

A recent study has found that women have up to 15% more brain cell density in the frontal lobe, which controls so-called higher mental processes, such as judgement, personality, planning and working memory. However, as they get older, women appear to shed cells more rapidly from this area than men. By old age, the density is similar for both sexes. It is not yet clear what impact, if any, this difference has on performance.

Witelson, S.F., Kigar, D.L. & Stoner-Beresh, H.J. 2001. Sex difference in the numerical density of neurons in the pyramidal layers of human prefrontal cortex: a stereologic study. Paper presented to the annual Society for Neuroscience meeting in San Diego, US.

http://news.bbc.co.uk/hi/english/health/newsid_1653000/1653687.stm

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