Schizophrenia and handedness

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This has been making the headlines:

http://www.healthline.com/health-news/m ... ked-110713

However, I think this study wasn't done very well, and the people talking about it miss the point. They only asked about which hand the patients preferred to write with, not getting a very good measurement of handedness. If you took a more complete survey of handedness, by also asking what, say, they prefer to throw or kick a ball with, then you can get a more complete picture.

Numerous studies have shown that pure left-handedness and pure right-handedness ("pure" meaning you use that hand preferentially for just about everything) is not associated with an increased risk for schizophrenia, but that mixed-handedness (where you use different hands for different things or are even inconsistent with which hand you use for particular tasks) is associated with an increased risk for schizophrenia. The reason why increased left-handedness is shown in the above study, I think, is because mixed-handed people are more likely to use their left hand to write than people who are not mixed-handed, at least in Western countries.

It's mixed-handedness that has the potential to be pathological, because it may reflect a failure of the brain to lateralize and specialize certain functions on certain sides of the brain properly. This failure of lateralization and specialization causes increased complexity in communication within the brain, bringing with it a higher rate of miscommunication within the brain.

Here's a study that looked more closely at mixed-handedness:

http://www.ncbi.nlm.nih.gov/pubmed/8771226

Other such studies exist. Just search "mixed-handedness schizophrenia".

Here's something else showing increased incidence of mental health problems associated with mixed-handedness:

http://www.sciencedaily.com/releases/20 ... 094511.htm

Yoo hoo! Correlation is NOT causation.

ruveyn

I am a left handed painter, among other things.
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Interesting links, thank you for posting those. Though I agree with ruveyn and would add researchers have a long way to go with all this labeling and categorizing.

I'm mixed-handed and I had psychotic depression in the past. I do worry sometimes that I might have latent schizophrenia, but I'm mentally quite healthy at the moment - so I don't think it's likely (hopefully.) Interesting, but more study is needed.