Handedness in schizophrenia and affective disorders: a large-scale cross-disorder study

Abstract

While most people are right-handed, a minority are left-handed or mixed-handed. It has been suggested that mental and developmental disorders are associated with increased prevalence of left-handedness and mixed-handedness. However, substantial heterogeneity exists across disorders, indicating that not all disorders are associated with a considerable shift away from right-handedness. Increased frequencies in left- and mixed-handedness have also been associated with more severe clinical symptoms, indicating that symptom severity rather than diagnosis explains the high prevalence of non-right-handedness in mental disorders. To address this issue, the present study investigated the association between handedness and measures of stress reactivity, depression, mania, anxiety, and positive and negative symptoms in a large sample of 994 healthy controls and 1213 patients with DSM IV affective disorders, schizoaffective disorders, or schizophrenia. A series of complementary analyses revealed lower lateralization and a higher percentage of mixed-handedness in patients with major depression (14.9%) and schizophrenia (24.0%) compared to healthy controls (12%). For patients with schizophrenia, higher symptom severity was associated with an increasing tendency towards left-handedness. No associations were found for patients diagnosed with major depression, bipolar disorder, or schizoaffective disorder. In healthy controls, no association between hand preference and symptoms was evident. Taken together, these findings suggest that both diagnosis and symptom severity are relevant for the shift away from right-handedness in mental disorders like schizophrenia and major depression.

Keywords: Bipolar; Depression; FOR2107; Hemispheric asymmetries; Laterality; Schizoaffective.

Fig. 1

Relative frequency of left-, mixed- and right-handers in patients and healthy controls. The percentage of left-, mixed- and right-handers is shown in patients (dark grey) and healthy controls (striped grey). * p < 0.05

Fig. 2

Proportion of left-, mixed-, and right-handedness in healthy controls and distinct patient groups. HC: Healthy controls; MDD: Major depressive disorder; BD: Bipolar disorder; SCA: Schizoaffective disorder; SCZ: Schizophrenia, * p < 0.05 (uncorrected)

Fig. 3

Heatmap of Pearson’s r for symptom-specific associations between handedness and cross-sectional clinical severity measures for all groups. A negative r (blue colors) indicates higher symptom severity / higher values for a parameter with lower LQ (i.e., increasing tendency towards left-handedness). A positive r (red colors) indicates higher symptom severity with higher LQ (i.e., increasing tendency towards right-handedness). R-values around zero (yellow colors) indicate weak associations between LQ and symptom severity