Left-handedness among a community sample of psychiatric outpatients suffering from mood and psychotic disorders

The human brain develops asymmetrically, such that certain cognitive processes arise predominantly from the left or right side. It has been proposed that variations in this laterality contribute to certain forms of mental illness, such as schizophrenia. A convenient measure of brain laterality is hand dominance, and prior work has found that patients with schizophrenia are more likely to be left-handed than the general population. This finding is not consistent, however, and fewer studies have directly compared handedness between psychiatric diagnoses. We assessed hand dominance in 107 patients presenting to an outpatient psychiatric clinic with diagnoses of a mood or psychotic disorder. The prevalence of left-handedness was 11% for mood disorders, which is similar to the rate in the general population. It was 40% in those with psychotic disorders (adjusted odds ratio = 7.9, p <.001). The prevalence of left-handedness was much higher in psychotic disorders compared with mood disorders in this community mental health sample.