The majority of clients diagnosed with schizophrenia have an IQ that resides below the normal range, or declines below the normal range as the disorder progresses. “In apparent contradiction to this view, some patients with schizophrenia have been documented to have an overall IQ in the normal range, and a few have above-average performance, at least in some neuropsychological domains,” said James. H. MacCabe of the Department of Psychosis Studies at the Institute of Psychiatry at King’s College in London. “If it were truly possible to have schizophrenia with no cognitive impairment, then this would have important implications for current etiological and neuropsychological models of schizophrenia, since cognitive deficits could not be regarded as a necessary condition for the illness.”
In an effort to determine if cognitive functioning is truly a feature of schizophrenia, MacCabe evaluated 34 clients with schizophrenia and an average IQ of 120. The participants were separated into two groups, one of which had realized a decline in IQ after diagnosis, the other of which had maintained their premorbid IQ. The participants completed a series of neuropsychological tests and their results were compared to those of healthy controls and schizophrenic clients with premorbid IQ’s below the normal range. The results revealed significant differences in performance. “Schizophrenia patients whose estimated premorbid and current IQ both lay in the superior range were statistically indistinguishable from IQ-matched healthy controls on all neurocognitive tests,” said MacCabe. “However, their profile of relative performance in subtests was similar to that of typical schizophrenia patients. Patients with superior premorbid IQ and evidence of intellectual deterioration had intermediate scores.” MacCabe noted that his findings reflect those of previous studies, confirming that some individuals with superior intelligence still meet the criteria for a diagnosis of schizophrenia. He added, “Our data indicate that within these patients, some undergo a decline in cognitive functioning and develop cognitive deficits that are similar to those of typical schizophrenia patients, but of a lesser degree.”
MacCabe, J. H., Brébion, G., Reichenberg, A., Ganguly, T., McKenna, P. J., Murray, R. M., & David, A. S. (2011, December 26). Superior Intellectual Ability in Schizophrenia: Neuropsychological Characteristics. Neuropsychology. Advance online publication. doi: 10.1037/a0026376
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