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Patterns of neurocognitive impairment in first-episode bipolar disorder and schizophrenia

  • Suzanne L. Barrett (a1), Ciaran C. Mulholland (a2), Stephen J. Cooper (a2) and Teresa M. Rushe (a3)

Abstract

Background

Researching psychotic disorders in unison rather than as separate diagnostic groups is widely advocated, but the viability of such an approach requires careful consideration from a neurocognitive perspective.

Aims

To describe cognition in people with bipolar disorder and schizophrenia and to examine how known causes of variability in individual's performance contribute to any observed diagnostic differences.

Method

Neurocognitive functioning in people with bipolar disorder (n = 32), schizophrenia (n = 46) and healthy controls (n = 67) was compared using analysis of covariance on data from the Northern Ireland First Episode Psychosis Study.

Results

The bipolar disorder and schizophrenia groups were most impaired on tests of memory, executive functioning and language. The bipolar group performed significantly better on tests of response inhibition, verbal fluency and callosal functioning. Between-group differences could be explained by the greater proclivity of individuals with schizophrenia to experience global cognitive impairment and negative symptoms.

Conclusions

Particular impairments are common to people with psychosis and may prove useful as endophenotypic markers. Considering the degree of individuals' global cognitive impairment is critical when attempting to understand patterns of selective impairment both within and between these diagnostic groups.

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Copyright

Corresponding author

Suzanne Barrett, Division of Psychiatry and Neuroscience, Queens University Belfast, Whitla Medical Building, 97 Lisburn Road, Belfast BT9 7BL, UK. Email: s.l.barrett@qub.ac.uk

Footnotes

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Declaration of interest

None.

Footnotes

References

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Patterns of neurocognitive impairment in first-episode bipolar disorder and schizophrenia

  • Suzanne L. Barrett (a1), Ciaran C. Mulholland (a2), Stephen J. Cooper (a2) and Teresa M. Rushe (a3)
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eLetters

The relation between general and selective impairment

Maurits Van den Noort, Visiting Professor, Cognitive Neuroscientist
08 December 2009

It is with great interest that we read the article in the July 2009 issue by Barrett et al(1) on patterns of neurocognitive impairment in first-episode bipolar disorder and schizophrenia. The authors rightly stated that considering the degree of an individual's global cognitive impairment is critical when attempting to understand patterns of selectiveimpairment, and that despite the vivid discussions about the non-specific profile of multiple cognitive deficits in individuals with schizophrenia, this link between the general and selective impairment in individuals has indeed been clearly under stressed in the literature.

However, there are a few critical remarks that we would like to make with respect to their highly interesting study and results. First, Barrettet al have used the Digit Span Forward/Backward from the Wechsler Memory Scale in order to test for verbal attention and working memory. However, it is important to note that with the Digit Span Forward/Backward working memory capacity cannot be tested properly, since it only taps the storage component and not the processing components that are also needed for real working memory tasks.(2) Therefore, it would have been better if the authors had used a so called: "complex" verbal working-memory measure thattaps both the storage and processing components, like; for instance, the Reading Span Test(2) or the Letter Number Sequencing Task out of the WAIS-III.(3)

Moreover, the fact that the schizophrenia group had significantly higher scores on the BDI than the bipolar disorder group might have influenced the scores on the neurocognitive battery in favour of the latter group, since previous research has shown that depression leads to impairments in cognition.(4) Therefore, this is a factor that should be better controlled for when bipolar disorder and schizophrenia are comparedin future studies.

Finally, although we totally agree with the authors that there are problems with the diagnostic classification of people with schizophrenia, their suggestion to divide individuals with psychosis into separate groups; according to whether they fall above or below 1 standard deviationof the expected mean, has limitations too. The main problem here is the variability in performance scores of individuals with psychosis on IQ tests.(5) As a result; their IQ scores can vary substantially between different measurement times so that individuals with psychosis can fulfillthe standards of a "preserved" IQ on one day, whereas several days later they do not.

References

1) Barrett SL, Mulholland C, Cooper SJ, Rushe TM. Patterns of neurocognitive impairment in first-episode bipolar disorder and schizophrenia. Br J Psychiatry 2009; 195: 67-72.

2)Van den Noort M, Bosch P, Haverkort M, Hugdahl K. A standard computerized version of the Reading Span Test in different languages. Eur J Psychol Assess 2008; 24: 35-42.

3)Wechsler D. Wechsler Adult Intelligence Scale-III (WAIS-III) Manual. Psychological Corporation, 2000.

4)Weiland-Fiedler P, Erickson K, Waldeck T, Luckenbaugh DA, Pike D, Bonne O, et al. Evidence for continuing neuropsychological impairments in depression. J Affect Disord 2004; 82: 253-8.

5)Goldstein G, Watson JR. Test-retest reliability of the Halstead-Reitan Battery and the WAIS in a neuropsychiatric population. Clin Neuropsychol 1989; 3: 265-72.
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Conflict of interest: None Declared

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