Laterality effects in schizophrenia and bipolar disorder

Abstract

There are numerous reports in the literature of lateralised structural cerebral abnormalities and alterations of the corpus callosum in the major psychoses. In the light of these findings the purpose of this study was to directly compare hemispheric differences and callosal interhemispheric transmission (IT) in schizophrenia and bipolar disorder. To do that we tested schizophrenic (SCZ), bipolar disorder (BD) patients and controls in a simple manual reaction time (RT) task with lateralised visual stimuli (Poffenberger paradigm) which enables one to test both laterality effects and IT time. We found an overall slowing of responses with the right hand in schizophrenics but not in bipolar patients, who, like controls, showed no hand differences. This selective slowing down of the right hand is likely to be related to abnormalities of intrahemispheric cortico-cortical connections in the left hemisphere. In contrast, IT time was similar in SCZ and BD patients and did not differ with respect to controls. Two are the novel findings of the present study: first both SZC and BD share a normal IT of visuomotor information despite the presence of callosal abnormalities. Second, an impairment of intrahemispheric left hemispheric processing is present only in SCZ patients. This represents a potentially important clue to a further understanding of the pathogenetic differences between the two major psychoses.

Similar white matter changes in schizophrenia and bipolar disorder: A tract-based spatial statistics study

“…These findings confirm that inter-hemispheric connectivity is hindered in both the disorders [7], representing a common neural underpinning of major psychoses [35][75][76]. The corpus callosum is known to play a fundamental role by modulating inter-hemispheric communication and cognitive processes [77][78].…”

“…With regard to BD, findings are not always in agreement, as suggested by previous studies from our group [34][35] and other independent studies [36][37]. Nonetheless, the majority of these studies detected a decrease in FA, which could be related to disruption of WM.…”

Grey matter differences in bipolar disorder: a meta‐analysis of voxel‐based morphometry studies

“…For example, based on communal evidence of callosal abnormalities in both bipolar disorder and schizophrenia (e.g., 56, 57), Bellani et al. (58) investigated laterality effects in patients with these conditions in comparison with healthy controls using a visual task. The task consisted of a simple manual reaction time task with lateralized visual stimuli designed to test laterality effects.…”

Effect of Lateralization on Motor and Mental Speed in Bipolar Disorder

“…Many findings have indicated hemispheric specialization abnormalities both in bipolar disorder and schizophrenia (3)(4)(5). Generally, right (non-dominant) hemisphere insult has been implicated in mood disorders (6,7), whereas left hemispheric dysfunction has been observed more frequently in schizophrenia (see review 8).…”