Independent frontal-system deficits in schizophrenia: cognitive, clinical, and adaptive implications

Abstract

This study examined whether frontal-system impairments in schizophrenia occur independently of one another and whether they have distinct implications for information processing, symptom severity, and adaptive functioning. We assessed 26 medication-free schizophrenic outpatients and 18 normal control subjects on eight frontally mediated tasks, semantic information processing, IQ, the BPRS, and long-term psychosocial adaptation. Schizophrenic subjects showed three types of deficits, which were uncorrelated with one another: (1) Executive dysfunction (inflexible problem solving) was related to decreased use of expectancy during controlled semantic priming, lower intelligence, more severe negative symptoms and stereotyped mannerisms. (2) Disinhibition of responses (to irrelevant stimuli) was associated with increased automatic priming, a trend for more severe hallucinations, and was unrelated to intelligence. (3) Motor dyscoordination (inaccurate, dysfluent motor sequencing) was not related to semantic processing, intelligence, or symptoms. Furthermore, all three impairments were unrelated to generalized slowness, age, sex, illness length, or pre-washout neuroleptic dose. Two deficits accounted for aspects of long-term psychosocial adaptation, even after statistical correction for IQ: Executive dysfunction was associated with younger illness onset, poor purposefulness and planning, impaired social relations, and lower global functioning. Motor dyscoordination was associated with poor treatment outcome and restricted educational advancement. Furthermore, executive and motor deficits interacted significantly; subjects who had both deficits showed the least favorable treatment outcome. These findings are neither consistent with generalized impairment nor with a unitary 'frontal syndrome' in schizophrenia. They provide preliminary evidence for at least three frontal-system deficits (dorsolateral, orbital, and premotor), which are dissociable from one another, can occur without general intellectual impairment, and have distinct implications for long-term adaptive functioning.