Study: Left-handed people have higher rates of schizophrenia, other psychotic disorders

Your dominant hand may be an indicator of your predisposition to certain psychotic disorders, such as schizophrenia, according to a new study by Yale University researchers.

"The human brain develops asymmetrically, such that certain cognitive processes arise predominantly from the left or right side," the study says.

Scientists believe that these variations in laterality--the preference most people show for one side of the body or another--may be a factor in certain forms of mental illness, such as schizophrenia.

A team led by Jason Webb, a child and adolescent psychiatry fellow at the Yale Child Study Center, looked at 107 individuals from a public outpatient psychiatric clinic in an urban, low-income community to determine the frequency of left-handedness within the group of patients with different types of mental disorders.

About 10% of the U.S. population is left-handed, and the research team found that the percentage of those diagnosed with mood disorders is in line with that--11% of people with mood disorders like depression and bipolar disorder are left-handed, according to the study. But when researchers looked at rates of psychotic disorders, they found that a striking 40% of those with schizophrenia or schizoaffective disorder are left-handed. The findings were published in the October-December issue of the journal SAGE Open.

"In general, people with psychosis are those who have lost touch with reality in some way, through hallucinations, delusions, or false beliefs, and it is notable that this symptom constellation seems to correlate with being left-handed," Webb told Yale News. "Finding biomarkers such as this can hopefully enable us to identify and differentiate mental disorders earlier, and perhaps one day tailor treatment in more effective ways."

- see the study (PDF)
- read the Yale News item

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