Evidence for reduced somatosensory lateralisation and focalisation in schizophrenia

Neuroimaging studies indicate diminished lateralisation of cerebral activity during motor tasks and language processing in schizophrenia. Some evidence also indicates that decreased lateralisation is accompanied by more diffuse intra-hemispheric activation, suggesting that diminished lateralisation might be part of a more general diminution of regional functional specialisation. In the case of passive processing of elementary somatosensory stimuli, evidence for decreased lateralisation derived from event-related potential studies, is conflicting. The greater spatial resolution of functional magnetic resonance imaging (fMRI) offers the potential to resolve this conflict. We report an fMRI study of 22 right-handed individuals with schizophrenia, 21 right-handed healthy individuals and 10 non-right-handed healthy individuals, designed to test the hypothesis that in schizophrenia there is a diminution of both lateralisation and intra-hemispheric focalisation during the passive processing of vibrotactile stimuli delivered to the right index finger. Significantly reduced lateralisation of activity in primary somatosensory cortex (SI) was observed in the schizophrenia group as compared to the healthy right-handed group. There was a trend for a reduction in SI lateralisation in the schizophrenia group compared to the healthy non-right-handed group. Contralateral SI focalisation was also significantly reduced in the schizophrenia group compared to both healthy groups. SI focalisation was negatively correlated with severity of disorganisation symptoms in the schizophrenia group. These results support the hypothesis that a generalised loss of functional specialisation is fundamental to schizophrenia.