Specificity of Cognitive Deficits in Bipolar Disorder versus Schizophrenia

Abstract

Background: More and more epidemiological, genetic and neuroimaging studies show similarities between bipolar disorder (BD) and schizophrenia (SZ). Cognitive functions are known to be highly impaired in SZ and are increasingly studied in BD. When both populations are compared, the conclusions appear to be contradictory. The purpose of this review is to help define the profile of cognitive deficits in BD and in SZ. Methods: A systematic review of the literature of neuropsychological studies comparing BD and SZ was made, beginning in January 1990 and ending in January 2005. Thirty-eight studies met the required quality criteria and were included in this review. Results: Bipolar patients exhibit extensive cognitive abnormalities with a pattern of deficits that is not unique to this disease. However, when compared to schizophrenic patients, bipolar patients demonstrate a lesser degree of deficits, particularly concerning premorbid and current intelligence quotient and perhaps attention, verbal memory and executive functions. When looking into effect sizes, there seem to be different profiles even in studies finding no significant differences. Conclusions: The neuropsychological differences reported between both groups could be due to the presence of psychotic features, to environmental factors (stressful events, duration of the disease and number of hospitalisations) and could also be related to differences during the neurodevelopmental phase. Further studies should confirm whether these results are truly related to different neurobiological backgrounds.

Genetic Variations of Human Neuropsin Gene and Psychiatric Disorders: Polymorphism Screening and Possible Association with Bipolar Disorder and Cognitive Functions

“…The evidence for the former association (with attention/concentration) was weak and it would not be significant any more after correcting for multiple testing; however, the latter association (with verbal IQ) was highly significant and remained significant even when multiple testing was taken into consideration. Since bipolar disorder shows a wide range of cognitive deficits, including memory and IQ (Schretlen et al, 2007;Daban et al, 2006), the observed impact on intelligence may have some relevance to susceptibility to bipolar disorder. However, given that deficits in intelligence and memory are generally worse in schizophrenia than in bipolar disorder, alterations in hNP may have some effects specific to molecular mechanisms of bipolar disorder.…”

Brief cognitive assessment instruments in schizophrenia and bipolar patients, and healthy control subjects: A comparison study between the Brief Cognitive Assessment Tool for Schizophrenia (B-CATS) and the Screen for Cognitive Impairment in Psychiatry (SCIP)

“…Therefore cognitive impairments are among the most promising candidate endophenotypes (Heinrichs and Zakzanis, 1998;Toulopoulou et al, 2007) either of psychosis or its premorbid stages, such as early or transitional phase of psychosis (Heinrichs and Zakzanis, 1998;Brewer et al, 2005). Neuropsychological deficits are highly prevalent in schizophrenia and bipolar disorder (Daban et al, 2006;Krabbendam et al, 2005;Seidman et al, 2010) and other psychoses, such as schizoaffective disorder (Reichenberg et al, 2009). Although there is still considerable debate regarding the extent to which cognitive deficits and psychopathological symptoms are related, recent reviews and meta-analyses suggest that cognitive impairment and symptoms in schizophrenia are independent or semi-independent dimensions of the illness, since only small to medium significant statistical associations between negative and disorganization dimensions of psychosis and cognitive impairment have been found (Dominguez et al, 2009;Nieuwenstein et al, 2001;Ventura et al, 2000).…”

Neuropsychological Functioning in Bipolar Disorder and Schizophrenia

“…Comparisons of cognitive functioning in SZ and BD have been reported (Daban et al 2006). Seidman et al (2002) compared 15 patients with BD, 87 with SZ, and 94 healthy controls (NC) using cognitive tests assigned to eight domains.…”