A recent large-scale study has found a compelling link between handedness and the severity of mental health symptoms in individuals diagnosed with schizophrenia and affective disorders. The research, conducted on over 1,200 patients in Germany, reveals that left-handedness and mixed-handedness are associated with more severe symptoms in schizophrenia, while the findings are more nuanced for affective disorders like major depression and bipolar disorder. The findings were published in the journal European Archives of Psychiatry and Clinical Neuroscience.
This discovery sheds new light on the potential role of brain lateralisation in mental health, suggesting that the way the brain is “wired” could influence the severity of psychiatric symptoms. While the link between handedness and diagnosis-specific symptoms was particularly pronounced in schizophrenia, the researchers found that these associations were not as significant in individuals with major depressive disorder (MDD) or bipolar disorder.
For patients with schizophrenia, the study found that left-handed individuals displayed higher symptom severity across various measures. In particular, left-handed patients had the highest scores for symptoms such as hallucinations and delusions, as well as negative symptoms, which include emotional flatness and withdrawal. These findings suggest a clear symptom-specific association between handedness and the severity of mental health issues in schizophrenia.
Annakarina Mundorf from MSH Medical School Hamburg noted: “It has been thought for some time that there may be a link between increased rates of left-handedness and mental health difficulties, as well as higher stress reactivity. However, in recent years, meta-analyses have indicated a potential link between increased rates of mixed-handedness and psychiatric disorders.”
Interestingly, the researchers also found a higher proportion of mixed-handedness in schizophrenia patients compared to healthy controls and individuals with other affective disorders. This points to the possibility that atypical brain lateralisation, which is reflected in handedness, could play a key role in the development and intensity of symptoms in schizophrenia. Mundorf added, “Patients, regardless of their diagnosis, exhibited a notable increase in mixed-handedness rates (15.7%) when compared to healthy controls (12%). Patients with schizophrenia (24%), then those with major depression (14.9%), showed the greatest increase in mixed-handedness.
In contrast, the study showed less pronounced associations between handedness and symptom severity in individuals with affective disorders, such as MDD and bipolar disorder. While there was a slight increase in symptom severity for left-handed patients, the results did not reach statistical significance for most symptom measures. This suggests that while handedness may play a role in these disorders, it is not as central as it appears to be in schizophrenia.
Mundorf’s insights provide further depth to this understanding. She observed, “A noteworthy finding was that, in patients with schizophrenia, left-handers exhibited the highest symptom severity, which lends support to the notion of a symptom-specific association.”
The study’s findings could pave the way for further research into how brain lateralisation influences mental health. While previous studies have suggested a genetic component to both handedness and mental disorders, this research highlights the importance of exploring how the brain’s structure and function may be linked to specific symptoms. The study’s authors suggest that future research could examine how treatment methods, such as neuromodulation techniques like transcranial magnetic stimulation, may impact brain asymmetries and potentially alleviate symptoms.
Looking ahead, Mundorf outlined plans for future research: “In the future, we intend to investigate changes in lateralisation at the neuronal level using functional magnetic resonance imaging (fMRI) data. Left-handers exhibit considerable variability in brain lateralisation, defined as the hemisphere where specific functions such as language or spatial attention are lateralised. Unfortunately, less is known about variability in brain lateralisation in mixed-handers.” She emphasised that further research in larger and more diverse samples is essential for a more comprehensive understanding of these associations.
The findings highlight the potential of integrating knowledge about brain lateralisation into clinical practice, particularly for schizophrenia, where handedness may serve as an important factor in treatment. “A personalised approach, as opposed to the use of standard procedures, may prove to be more efficacious in achieving treatment success,” Mundorf concluded.
