Functional laterality refers to a natural asymmetry in left or right-side dominance, for example in terms of handedness, or brain function. Handedness refers to the preference for using one hand over the other for certain tasks. Right-handed people show increased dexterity in their right hand, left-handed people show increased ability the left hand. People may also be ‘mixed’ handed and show different hand preference for different tasks. Listening tasks can be used to assess language lateralisation. People with schizophrenia may show differences in handedness or footedness, as well as altered visual and auditory dominance that may reflect abnormalities in brain laterality and dominance.

What is the evidence for altered functional laterality?

High quality evidence shows that people with schizophrenia are more likely to be left or mixed-handed than people without schizophrenia, including people with other psychiatric disorders. Moderate to high quality evidence suggests this finding is similar for males and females. Moderate to high quality evidence suggests people with schizophrenia have less right-ear dominance, which may be most apparent in people who experience auditory hallucinations. Moderate to low quality evidence suggest people with schizophrenia show an absence of normal leftward asymmetry in the planum temporale and Sylvian fissure brain regions, and an excess rightward asymmetry in the superior temporal gyrus (particularly posterior). There is also a higher frequency of abnormal (reversed) asymmetry in the frontal and occipital lobes.

February 2022

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