cognitive reserve

Learning another language boosts white matter

November, 2012

Foreign language learning increases the white matter in the language network and the bridge joining the hemispheres, perhaps helping explain why bilinguals have better executive control.

In my last report, I discussed a finding that intensive foreign language learning ‘grew’ the size of certain brain regions. This growth reflects gray matter increase. Another recent study looks at a different aspect: white matter.

In the study, monthly brain scans were taken of 27 college students, of whom 11 were taking an intensive nine-month Chinese language course. These brain scans were specifically aimed at tracking white matter changes in the students’ brains.

Significant changes were indeed observed in the brains of the language learners. To the researchers’ surprise, however, the biggest changes were observed in an area not previously considered part of the language network: the white matter tracts that cross the corpus callosum, the main bridge between the hemispheres. (I’m not quite sure why they were surprised, since a previous study had found that bilinguals showed higher white matter integrity in the corpus callosum.)

Significant changes were also observed within the left-hemisphere language network and in the right temporal lobe. The rate of increase in white matter was linear, showing a steady progression with each passing month.

The researchers suggest that plasticity in the adult brain may differ from that seen in children’s brains. While children’s brains change mainly through the pruning of unwanted connections and the death of unwanted cells, adult brains may rely mainly on neurogenesis and myelinogenesis.

The growth of new myelin is a process that is still largely mysterious, but it’s suggested that activity at the axons (the extensions of neurons that carry the electrical signals) might trigger increases in the size, density, or number of oligodendrocytes (the cells responsible for the myelin sheaths). This process is thought to be mediated by astrocytes, and in recent years we have begun to realize that astrocytes, long regarded as mere ‘support cells’, are in fact quite important for learning and memory. Just how important is something researchers are still working on.

The finding of changes between the frontal hemispheres and caudate nuclei is consistent with a previously-expressed idea that language learning requires the development of a network to control switching between languages.

Does the development of such a network enhance the task-switching facility in working memory? Previous research has found that bilinguals tend to have better executive control than monolinguals, and it has been suggested that the experience of managing two (or more) languages reorganizes certain brain networks, creating a more effective basis for executive control.

As in the previous study, the language studied was very different from the students’ native language, and they had no previous experience of it. The level of intensity was of course much less.

I do wonder if the fact that the language being studied was Mandarin Chinese limits the generality of these findings. Because of the pictorial nature of the written language, Chinese has been shown to involve a wider network of regions than European languages.

Nevertheless, the findings add to the evidence that adult brains retain the capacity to reorganize themselves, and add to growing evidence that we should be paying more attention to white matter changes.

Reference: 

[3143] Schlegel, A. A., Rudelson J. J., & Tse P. U.
(2012).  White Matter Structure Changes as Adults Learn a Second Language.
Journal of Cognitive Neuroscience. 24(8), 1664 - 1670.

Bialystok, E., Craik, F. I. M., & Luk, G. (2012). Bilingualism: consequences for mind and brain. Trends in Cognitive Sciences, 16(4), 240–250. doi:10.1016/j.tics.2012.03.001

Luk, G. et al. (2011) Lifelong bilingualism maintains white matter integrity in older adults. J. Neurosci. 31, 16808–16813

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Old honeybees can regain youthful cognition when they return to youthful duties

August, 2012
  • A honey bee study shows how old foraging bees quickly start to decline cognitively, and how this can be reversed in some if they return to more social domestic duties in the hive.

I often talk about the importance of attitudes and beliefs for memory and cognition. A new honey bee study provides support for this in relation to the effects of aging on the brain, and suggests that this principle extends across the animal kingdom.

Previous research has shown that bees that stay in the nest and take care of the young remain mentally competent, but they don’t nurse for ever. When they’re older (after about 2-3 weeks), they become foragers, and foraging bees age very quickly — both physically and mentally. Obviously, you would think, bees ‘retire’ to foraging, and their old age is brief (they begin to show cognitive decline after just two weeks).

But it’s not as simple as that, because in artificial hives where worker bees are all the same age, nurse bees of the same age as foragers don’t show the same cognitive and sensory decline. Moreover, nurse bees have been found to maintain their cognitive abilities for more than 100 days, while foragers die within 18 days and show cognitive declines after 13-15 days (although their ability to assess sweetness remains intact).

The researchers accordingly asked a very interesting question: what happens if the foragers return to babysitting?

To achieve this, they removed all of the younger nurse bees from the nest, leaving only the queen and babies. When the older, foraging bees returned to the nest, activity slowed down for several days, and then they re-organized themselves: some of the old bees returned to foraging; others took on the babysitting and housekeeping duties (cleaning, building the comb, and tending to the queen). After 10 days, around half of these latter bees had significantly improved their ability to learn new things.

This cognitive improvement was also associated with a change in two specific proteins in their brains: one that has been associated with protection against oxidative stress and inflammation associated with Alzheimer disease and Huntington disease in humans (Prx6), and another dubbed a “chaperone” protein because it protects other proteins from being damaged when brain or other tissues are exposed to cell-level stress.

Precisely what it is about returning to the hive that produces this effect is a matter of speculation, but this finding does show that learning impairment in old bees can be reversed by changes in behavior, and this reversal is correlated with specific changes in brain protein.

Having said this, it shouldn’t be overlooked that only some of the worker bees showed this brain plasticity. This is not, apparently, due to differences in genotype, but may depend on the amount of foraging experience.

The findings add weight to the idea that social interventions can help our brains stay younger, and are consistent with growing evidence that, in humans, social engagement helps protect against dementia and age-related cognitive impairment.

The (probably) experience-dependent individual differences shown by the bees is perhaps mirrored in our idea of cognitive reserve, but with a twist. The concept of cognitive reserve emphasizes that accumulating a wealth of cognitive experience (whether through education or occupation or other activities) protects your brain from the damage that might occur with age. But perhaps (and I’m speculating now) we should also consider the other side of this: repeated engagement in routine or undemanding activities may have a deleterious effect, independent of and additional to the absence of more stimulating activities.

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Career choice may determine where frontotemporal dementia begins

October, 2010
  • An international review of patients with frontotemporal dementia has revealed that the area of the brain first affected tends to be the hemisphere least used in the individual’s occupation.

A review of brain imaging and occupation data from 588 patients diagnosed with frontotemporal dementia has found that among the dementias affecting those 65 years and younger, FTD is as common as Alzheimer's disease. The study also found that the side of the brain first attacked (unlike Alzheimer’s, FTD typically begins with tissue loss in one hemisphere) is influenced by the person’s occupation.

Using occupation scores that reflect the type of skills emphasized, they found that patients with professions rated highly for verbal skills, such as school principals, had greater tissue loss on the right side of the brain, whereas those rated low for verbal skills, such as flight engineers, had greater tissue loss on the left side of the brain. This effect was expressed most clearly in the temporal lobes of the brain. In other words, the side of the brain least used in the patient's professional life was apparently the first attacked.

These findings are in keeping with the theory of cognitive reserve, but may be due to some asymmetry in the brain that both inclines them to a particular occupational path and renders the relatively deficient hemisphere more vulnerable in later life.

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Larger head size may protect against Alzheimer's symptoms

August, 2010
  • Another study finding larger head size helps protect people with Alzheimer’s brain damage from cognitive impairment.

Confirming previous research, a study involving 270 Alzheimer’s patients has found that larger head size was associated with better performance on memory and thinking tests, even when there was an equivalent degree of brain damage. The findings are consistent with the theory of cognitive reserve. They also point to the importance of brain development early in life, since the brain reaches 93% of its final size at age six, and while partly determined by genes, brain growth is also influenced by nutrition, infections, and brain injuries.

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Mental activity may protect against memory problems in MS

July, 2010
  • A new study points to the importance of cognitive reserve to protect sufferers of multiple sclerosis for cognitive impairment.

Memory and learning problems often occur in multiple sclerosis, but bewilderingly, are only weakly associated with the severity of the disease. A study involving 44 people around the age of 45 who had MS for an average of 11 years has found that those with a mentally active lifestyle had good scores on the tests of learning and memory even if they had higher amounts of brain damage. The findings suggest that, as with Alzheimer’s disease, 'cognitive reserve' protects against cognitive impairment. Differences in cognitive reserve may explain why some people have memory problems early in the disease, while others do not develop memory problems until much later, if at all.

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