Atypical handedness in schizophrenia: Some methodological and theoretical issues

An updated review of the literature strongly supports the view that in schi zophrenia there is an atypical leftward shift in the handedness distributio n that, while comprising different subtypes, is characterized by a more var iable and less completely lateralized pattern of manual preference, referre d to as mixed handedness (MH) or ambiguous handedness (AH), Only two studie s revealed an increased prevalence of left-handedness suggestive of patholo gical left-handedness (PLH), This article also examines the current status of neurodevelopmental factors and mechanisms in schizophrenia that purport to explain these pathological shifts in handedness (PLH, MH, AH). Different theoretical positions were evaluated, each involving some aspect of left h emisphere insult (unilateral or bilateral). Finally, it was shown that thes e shifts predict certain key symptoms and neural substrates in schizophreni a including thought disorder, negative symptoms, neuropsychological impairm ent, family history, and brain anatomy. These subtypes may represent neurod evelopmental markers of insult during intrauterine life that are nongenetic in origin.