Turning it upside down: areas of preserved cognitive function in schizophrenia

Abstract

Patients with schizophrenia demonstrate marked impairments on most clinical neuropsychological tests. These findings suggest that patients suffer from a generalized form of cognitive impairment, with little evidence of spared performance documented in several large meta-analytic reviews of the clinical literature. In contrast, we review evidence for relative sparing of aspects of attention, procedural memory, and emotional processing observed in studies that have employed experimental approaches adapted from the cognitive and affective neuroscience literature. These islands of preserved performance suggest that the cognitive deficits in schizophrenia are not as general as they appear to be when assayed with clinical neuropsychological methods. The apparent contradiction in findings across methods may offer important clues about the nature of cognitive impairment in schizophrenia. The documentation of preserved cognitive function in schizophrenia may serve to sharpen hypotheses about the biological mechanisms that are implicated in the illness.

Figure 1

Meta-Analytic results adapted from Dickinson, Ramsey, & Gold 2007. The meta-analysis synthesized data from 37 studies involving 1961 patients with schizophrenia and 1444 healthy comparison subjects, and found that the largest effect size documented in the clinical neuropsychological literature was observed on digit symbol coding tasks.

Figure 2

Reaction time of patients with schizophrenia and normal control subjects in Posner-type visuospatial attention paradigms with target-predictive cues. The left graph presents averages across mean values reported by Bustillo et al (1997), Gold et al. (1992), Oie et al. (1998), Pardo et al. (2000), Posner et al. (1988), Wigal et al. (1997), and Strauss et al. (1991). These experiments include a total of 154 patients and 130 healthy controls. The right graph presents averages across mean values reported by Carter et al. (1992, and Bustillo et al. (1997) and is based on a total of 82 patients and 51 healthy controls.