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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.

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Background and Aims:Language disturbances, such as impoverishment, disorganization and dysregulation, are a prominent feature of schizophrenia. Several neuroimaging studies have suggested the superior temporal gyrus (STG) as a likely anatomical substrate of language deficits in schizophrenia. The aim of this study was to verify a correlation between structural measures of STG and Heschl's gyrus (HG) and language dimensions.Methods:An extensive language examination battery, which included narrative and conversational expressive tasks, and syntactic and pragmatic comprehension tests, was administered to 23 schizophrenia patients (mean age±SD= 40.30±11.60) and 21 normal controls (mean age±SD= 42.19±11.05). All subjects also underwent a 1.5T MRI session, and STG and HG were manually traced and volumes were obtained, bilaterally, using Brains2.Results:Specific language deficits were shown in subjects with schizophrenia compared to healthy individuals (p<0.001), particularly in verbal fluency, syntactic complexity, lexical diversity and metaphor/idiom comprehension. Interestingly, speech fluency significantly directly associated with left STG gray matter volumes in controls (r=0.46, p=0.03) but not in patients (r=-0.27, p=0.21). In contrast, complex syntax and word diversity significantly correlated, respectively, with left and right HG volumes in schizophrenia patients (r=0.45, p=0.02; r=-0.47, p=0.02), but not in controls (p>0.05).Conclusions:This study confirmed a widespread impairment of language in schizophrenia. Interestingly, distinct language dimensions differently correlated with STG-HG volumes in patients with schizophrenia and controls, particularly with regard to verbal fluency and syntactic measures.

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Background:Several neuroimaging studies have shown impaired microstructural integrity of corpus callosum in schizophrenia, which may support inter-hemispheric misconnection. However, functional connectivity has rarely been investigated in schizophrenia.Objectives:To explore inter-hemispheric communication in a sample of patients with schizophrenia in comparison to healthy controls.Methods:Twenty-five patients with schizophrenia and forty-one healthy controls were studied. Subjects were asked to press a key with the index-finger of their right or the left hand as quickly as possible following appearance of either a single or a double stimulus. Two measures were calculated: the difference between manual reaction times (RT) after the presentation of single stimuli to the ipsilateral (uncrossed response) or contralateral (crossed response) visual hemifield (the so-called Poffenberger Paradigm), as a measure of interhemispheric transfer time (ITT), and the difference between double and single stimuli (the Redundant Target Effect, RTE), as a measure of interhemispheric integration.Results:Overall, patients with schizophrenia responded faster with the left than with the right hand (Paired sample t-test p=0.019). Importantly, in schizophrenics there was no group difference in ITT but there was a significantly enhanced RTE .Conclusions:The slower RT for right hand in schizophrenics possibly reflects a general delay of the left cerebral hemisphere in visuomotor RT. Moreover, the enhanced RTE suggests an impairment of interhemispheric integration in schizophrenia.