Although intellectual and neurocognitive deficits accompany schizophrenia, there are inconsistencies in the literature concerning issues of intellectual decline, premorbid deficits, a modal deficit pattern, and preserved abilities.
A battery of neuropsychological tests was administered once to 117 consecutively admitted patients with chronic schizophrenia and a group of 27 healthy control subjects to examine patterns of premorbid and current intellect (measured by means of reading scores and IQ, respectively) and the attendant cognitive profiles in schizophrenia using classification methods based on clinically derived (IQ levels) and atheoretical (cluster) techniques.
Sixty patients (51%) with schizophrenia who displayed a general intellectual decline of 10 points or greater from estimated premorbid levels also exhibited deficits of executive function, memory, and attention. Twenty-eight patients (23%) with consistently low estimated premorbid intellect and current intellectual levels who displayed no evidence of IQ decline exhibited language and visual processing deficits in addition to deficits present in the intellectually declining group. The remaining 29 patients (25%) who displayed average estimated premorbid intellectual levels did not show IQ decline and exhibited a cognitive profile similar to normal, with the exception of executive function and attention impairment. Atheoretical analyses support the findings from clinically derived subgroups.
These results suggest that IQ decline, although modal in schizophrenia, is not universally characteristic and that executive function and attention deficits may be core features of schizophrenia, independent of IQ variations.