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You find this advice all over the web: Use your non-dominant hand to do simple tasks such as brushing your teeth because it will make new brain cells grow.

On the other hand, it is suggested that it is potentially harmful to retrain left handed people to write with the right hand.

So, is there any evidence to support the first claim, i.e., that engaging the off-hand more in minor tasks fosters growth of brain cells?

EDIT: Some sources for where this claim is made:

I cannot further substantiate what "keeping your brain active" means because the sources I give also don't really substantiate it. But maybe there is some scientific research that is more specific.

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    Can you please add sources of the claim? Also, who says that neurogenesis is necessary to keep the brain "active"? And what does "keep the brain active" exactly mean? – nico Apr 2 '12 at 15:17
  • Well, if that's a minor daily task for you... – Lagerbaer May 6 '12 at 2:34
  • I can't answer directly, but I can raise a concern. I have heard these same claims, and without examining them too carefully I have come away with the thesis that doing things outside the biophysical comfort zone is supposed to cause the brain to grow new neural connections. The immediate conclusion people draw is that this is good. The brain is often pictured as a single entity that, like for example the bicep muscle, is either waxing or waning, growing or dying. But the brain is a complex multi-layered system, that is a single entity only in the same sense that Grand Central Station is. Addi – user7120 May 16 '12 at 3:13
  • Related question about re-training handedness: skeptics.stackexchange.com/questions/7282/… – ESultanik Jul 15 '15 at 20:02
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Per Michael Corballis, professor of cognitive neuroscience and psychology at the University of Auckland in a Scientific American 2013 article, "teaching people to become ambidextrous does not appear to improve brain function. It is possible to train your nondominant hand to become more proficient. A cooperative brain seems to work better than one in which the two sides compete".

Disadvantage due to natural ambidexterity in children

Evidence per studies listed below suggests that being ambidextrous from birth may associate with developmental problems.

  1. Per study by Corballis MC et.al. in 2008 of 11-year-olds in England, the results showed that those who are naturally ambidextrous are slightly more prone to academic difficulties than either left- or right-handers.

Evidence from a large-scale study of 11-year olds in Britain suggests that ambidextrous individuals may be disadvantaged in tests of verbal, nonverbal, reading, and mathematical skills relative to right- and left-handers, but this basic finding was not replicated in another study of younger boys in Germany. The data supports the earlier finding that ambidextrous individuals perform more poorly than left- or right-handers, especially on subscales measuring arithmetic, memory, and reasoning, and extend that finding to adults.

  1. Per study by Alina Rodriguez et.al. published in the journal Pediatrics in 2010, children who are mixed-handed, or ambidextrous, are more likely to have mental health, language and scholastic problems in childhood than right- or left-handed children.

The researchers concluded that “mixed-handed children have a greater likelihood of having language, scholastic and mental health problems in childhood”, and that “these persist into adolescence”. "The researchers do not think that ambidexterity directly causes the language or behavioural problems seen. Instead, they think that differences in the brain that affect hand dominance could also affect both these traits. At this stage, due to the limitations of this study, its results should be seen as very preliminary, and will require confirmation by other studies."

  1. Per study by David W. Johnston in 2009, the results showed that mixed-handed children perform significantly worse in nearly all measures of development than right-handed children, with the relative disadvantage being larger for boys than girls.

The most disadvantaged group was children with no hand preference (mixed-handers). The degree of disadvantage for mixed-handers was roughly double the disadvantage of left-handers relative to right-handers. These lower levels of performance corroborate the findings of recent large-scale studies of adults. The current results therefore support Crow et al.’s (1998) proposition that mixed-handedness and hemispheric indecision result in a suboptimal state in which cognitive abilities do not develop normally. Another possibility, however, is that children with mixed-handedness are developmentally delayed. Although hand preference may develop in the first year of life, the rate of development is variable (Michel et al. 2006). In summary, this research demonstrates a broad-based cognitive deficit in left- and mixed-handers relative to right-handers.

"The human condition itself might be summed up as the balance between the brain's asymmetries and symmetries. "Effects are slight, but the risks of training to become ambidextrous may cause similar difficulties. The two hemispheres of the brain are not interchangeable. The left hemisphere, for example, is typically responsible for language processing, whereas the right hemisphere often handles nonverbal activities. These asymmetries probably evolved to allow the two sides of the brain to specialize." Latest evidence shows that there is no general pattern between relative hand-skill and ability.

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    The studies mentioned in the section on ambidexterity show the association between developmental problems and being ambidextrous at birth. If natural ambidexterity itself leads to such problems, its imperative with logical reasoning to assume that the claims mentioned in the question should not be practiced. – pericles316 Jul 16 '15 at 12:22

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