Clinical utility of the dual n-back task in schizophrenia: A functional imaging approach.

The neural correlate of working memory (WM) impairment in schizophrenia is key to the understanding of the cognitive deficits observed in this disorder. We sought to determine the clinical validity of the dual version n-back paradigm in patients with schizophrenia, and whether schizophrenia patients exhibit altered brain activation patterns compared with healthy controls in this dual version WM measure using functional magnetic resonance imaging. Patients with schizophrenia (n = 20) and healthy controls (n = 24) performed the dual n-back task that consists of both visuospatial and auditory-verbal n-back streams, in which participants were required to monitor and update the contents from these two different inputs simultaneously. Significant positive correlations were found between performance in the dual 2-back condition and another measure of WM capacity and IQ estimates. Moreover, hypoactivation was observed at the right middle frontal gyrus and the posterior parietal regions in schizophrenia participants compared with healthy controls. The right hippocampus was less deactivated in schizophrenia patients compared with healthy controls. Our results support the clinical utility of the dual n-back task in schizophrenia and may have implications for the development of specific cognitive training targeting these impaired neural substrates in relation to WM in patients with schizophrenia.

Heritability estimates of spatial working memory and set-shifting in a healthy Chinese twin sample: A preliminary study.

Impairments in spatial working memory (SWM) and set-shifting abilities have both been consistently observed in individuals with schizophrenia and are considered to be potential endophenotypes of this illness. However, an endophenotype needs to fulfill a set of stringent criteria, including heritability. This study examined the heritability of these two functions in a healthy Chinese twin sample. Forty-five pairs of monozygotic (MZ) twins and 35 pairs of dizygotic (DZ) twins completed the SWM task and the Intra-Extra Dimensional Set-Shifting (IED) task of the Cambridge Neuropsychological Test Automated Battery (CANTAB). We found a moderate heritability for SWM, of which the familial/genetic factors accounted for 33% of the total variance. However, we failed to find any significant heritability for set-shifting ability, of which the specific environmental factor explained most of the variance (85%). The preliminary findings from this small healthy Chinese twin sample suggest that SWM is heritable, whereas the set-shifting ability may reflect "extra-genetic" influences.