Brief ReportsSpatial working memory: absence of gender differences in schizophrenia patients and healthy control subjects
Introduction
Relative to their male counterparts, female schizophrenia patients tend to experience a more benign course of illness, as demonstrated by fewer neuroanatomic abnormalities, later onset, superior premorbid adjustment, better outcome, longer periods of remission, and fewer readmissions Andreasen et al 1990, Angermeyer et al 1990, Goldstein et al 1998, Lewine 1988. Given such gender differences in the course of illness, it is possible that female schizophrenia patients may also manifest superior neurocognitive functioning relative to males. To date, no definitive pattern of gender differences in the neurocognitive profile of schizophrenia has been established Goldstein et al 1998, Haas et al 1990, Hoff et al 1992, Walker et al 1992.
However, recent studies suggest that gender differences in neuropsychological performance may be attributable to sexual dimorphism of the brain (e.g., Seidman et al 1997). Pathophysiology of schizophrenia includes local gray matter reduction in the frontal heteromodal association cortex (e.g., Pearlson et al 1996, Schlaepfer et al 1995). Healthy female brains have increased gray matter volume in the dorsolateral prefrontal cortex (DLPFC) relative to male brains (Schlaepfer et al 1995).
The DLPFC is essential in mediating working memory (WM) processes (see Goldman-Rakic 1991, Jonides et al 1993). Lesions in the DLPFC result in profound deficits in WM, as assessed by the DRT Freedman and Oscar-Berman 1986, Funahashi et al 1993. Schizophrenia patients also show similar deficits Carter et al 1996, Keefe et al 1995, Park and Holzman 1992, Park and Holzman 1993. Spatial WM, as assessed by the DRT, is associated with WCST scores (Park 1997, Park et al 1995. These results suggest that the DRT, mediated by the DLPFC, taps WM, and is associated with WCST. But the DRT offers advantages over traditional neuropsychological tests (e.g., WCST) because the neurobiologic basis of the DRT is well described and understood (see Goldman-Rakic 1991).
Although gender differences in WCST have been reported and interpreted as providing evidence for sexual dimorphism of DLPFC (Seidman et al 1997), gender differences in DRT performance have not been examined. Since the DRT is a much more circumscribed test of assessing the DLPFC, we examined the potential gender differences in spatial WM (and therefore, DLPFC function) by aggregating data from three previously published studies and by collecting additional DRT data from a new set of subjects.
Section snippets
Participants
Data from three previous studies of were aggregated (see the following papers for descriptions of participants, sampling procedures, and methods: Park and Holzman 1992, Park and Holzman 1993, Park et al 1999). New subjects were recruited and tested on the same DRT. This resulted in a sample of 71 schizophrenia patients who met the DSM criteria (26 females) and 213 normal control subjects (106 females). Subjects had no brain damage, were under 50 years old, and were not mentally retarded. All
Results
Within the schizophrenic group, there were no significant gender differences in age [t (69) = 1.28; p = .20], education [t (69) = 1.16; p = .25], or illness duration [t (69) = −1.10; p = .27]. There was a significant gender difference in age of onset [t (69) = 2.5; p = .01]; women had later onset. Within the control group, there were no significant gender differences in age [t (211) = 0.58; p = .56] or education [t (211) = 1.82, p = .07].
A two-way (group × sex) ANOVA was performed on the DRT
Discussion
We examined gender differences in spatial WM (as assessed by the DRT), mediated by the DLPFC, because recent neuroanatomic and neuropsychological data suggested gender differences in DLPFC structure and function Schlaepfer et al 1995, Seidman et al 1997. Seidman and colleagues (1997) found that male schizophrenic subjects perform significantly worse on the WCST than the female patients. They interpreted the results in the context of the sexual dimorphism of the DLPFC. Others, however, reported
Acknowledgements
This project was funded by the NIMH, NARSAD, and the Scottish Rite Schizophrenia Research Program.
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