An Update on Neurocognitive Impairment in Schizophrenia and Depression

Despite the considerable research that has been devoted to schizophrenia and depression over the last years, the understanding of the biological bases of these disabling disorders is still fragmentary. Adoption-, twin-and family studies, provide clear evidence of strong genetic components to these mental disorders, although multiple loci are likely to be involved. The effect of pharmacological intervention has hinted at specifi c neurotransmitter systems of etiological importance, but the lack of receptor specifi city of therapeutic drugs have thwarted any simple linkage of behavioural and molecular phenotypes. More recently brain imaging investigations , like PET and functional magnetic resonance imaging (fMRI), have identifi ed candidate structural and functional abnormalities, including work in identifying changes in networks of brain regions, but these fi ndings are still preliminary and need to be integrated with other accumulating knowledge. Of particular interest in the last decade that is adding to the complexity of the picture, is the realization that basic cognitive functions are seriously distorted, and that removal of core symptoms such as paranoia and hallucinations does not necessarily ameliorate the cognitive defi cits. It has also been shown that cognitive defi cits can occur before clinical symptoms in schizophrenia, in a prodromal phase of the disorder, pointing to a possible causal relationship between cognitive defi cits and outbreak of the disorder. Similarly, it has been reported that removing clinical symptoms in depression does not alleviate cognitive symptoms, like impaired concentration and focus of attention. However, it is still not possible to diagnose a patient from cognitive defi cits alone, or from a combination of clinical symptoms and cognitive defi cits, and structural and functional neuroimaging data, although promising, have also not found the way to routine clinical practice. The aim of the current special topic is to provide an update on research on cognitive and brain imaging research for the understanding of cognitive defi cits in these disorders, with a focus on recent developments in structural and functional neu-roimaging, including recent advances in tracking of white matter fi bres, and electroencephalography (EEG) and novel computational measures. Vince Calhoun et al. show how fMRI can be used not only to identifying regions where hemodynamic response amplitudes can differentiate between patient and control groups, but also how such amplitude based comparisons can estimate temporal correlations and compute maps of functional connectivity between regions. In their article, Calhoun et al. review work related to how these …