More left-handed among schizophrenics

More left-handed people are found among schizophrenics than in the general population. Brain researcher Marco Hirnstein believes that this is due to common genes between hand preference and the disease.

Model of the brain
BIG DIFFERENCE: In schizofrenics, along with left-handed people, the brain's language centre is more often found in the right hemisphere than is the case in right-handed people.
Eivind Senneset

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Approximately 10 per cent of the world population is left-handed and there are many myths about them. For example, it is said that left-handers are more creative and that there are collectively more geniuses among them compared with the right-handed majority. In addition, an unusually high percentage of American presidents favoured their left hand, although they cannot all necessarily be considered among the geniuses.


Confirming a myth about left-handers

Even though most of the myths about left-handers cannot be proven or are, at times, complete fiction, postdoctoral fellow Marco Andre Hirnstein from the Department of Biological and Medical Psychology at the University of Bergen (UiB) recently confirmed one of them.

“My research shows that more left-handers are found among schizophrenics than in the general population,” says Hirnstein, who is a member of the Bergen fMRI Group that is headed by Professor Kenneth Hugdahl, who held an Advanced Grant from the European Research Council (ERC), one of the most prestigious grants in the international research community, until the end of March 2015.

By reviewing 70 studies with around 10,000 participants, Hirnstein found that approximately 15 per cent of schizophrenics are not right-handed, compared with 10 per cent of the population as a whole. The results of Hirnstein's research were recently published in the academic journal, The British Journal of Psychiatry.


Connection may be hereditary

Hirnstein cannot establish for certain why there are more left-handers among schizophrenics than otherwise in the population. However, the connection is most likely hereditary.

“It is probably specific genes that, on the one hand, increase the risk of developing schizophrenia, while on the other, increase the chance of being left-handed,” he says.

However, the researcher is certain that the difference between being right-handed or left-handed is not in the hands, but in the brain. While, the left side of the brain controls the right hand, the right side of the brain controls the left hand.

“The brain is in fact organised a little differently for right-handers than for left-handers,” he says.

For example, for both schizophrenics and left-handers, the language centre is more commonly located in the right side of the brain than is the case for right-handers. While 95 per cent of right-handers have the language centre in the left side of the brain, this only applies for 70 per cent of non-right-handers.

Of the non-right-handers who do not have the language centre in the left side of the brain, half of these have the language centre in the right side of the brain and the other half have it in both sides of the brain. For schizophrenics, the language centre in the left side of the brain is also reduced.

“It is in the actual organisation and specialisation of the brain that I believe it is possible to find answers to parts of the schizophrenia riddle and the link between hand preference and schizophrenia,” Hirnstein says.


Stimulating neurons in the brain

He is an expert in so-called transcranial magnetic stimulation. A device the size of a hair dryer is placed against the head of the patient and creates a magnetic field that stimulates the neurons in the brain for a short period.

While fMRI scanning can say something about the areas of the brain that are active, the magnetic stimulation can tell researchers and health care personnel which areas are necessary for different activities. If, for example, a part of the brain is stimulated while another person is speaking, the speech will be changed and distorted if that area is necessary for understanding what the other person is saying.

Magnetic stimulation is also used for treatment and, among other things, has demonstrated good results in the treatment of depression. Hirnstein believes that magnetic stimulation can also assist in treating schizophrenics who hear voices.

“If it transpires that there is an imbalance in the brain activity that causes a person to hear voices, magnetic stimulation can regulate the activity in certain parts of the brain.”


Pharmacological treatment is long way off

He notes that the research into brain differences is still a long way off from offering pharmaceutical treatment.

“However, we have established that schizophrenia and brain specialisation are linked in some way or another. The next step is to determine exactly what the connection is. It is only when we have found a causal connection that we can hope to have better treatment,” Marco Hirnstein says.

This article is also published in the UiB Magazine 2015/2016. You can download a PDF of the full magazine or browse the magazine online.