Schizophrenia Neuropsychology

Pattern of cognitive deficits

There is growing awareness that cognitive deficits in schizophrenia represent a core feature of the disorder and cannot simply be dismissed as secondary consequences of psychotic symptoms (Breier 1999). The degree of cognitive impairment is greater in child and adolescent onset than in adult onset patients. A consistent finding in child and adolescent onset patients is a mean IQ of between 80 and 85 (1 SD below the population mean), with about one-third of cases having an IQ below 70 (Jacobsen & Rapoport 1998; Hollis 1999). This represents a mean IQ score about 10 points lower than the mean IQ in adult schizophrenia. These findings raise several important questions.
First, are the cognitive deficits specific or generalized: are some aspects of cognitive functioning affected more than others?
Secondly, which deficits precede the onset of psychosis and could be causal, and which are consequences of psychosis?
Thirdly, is the pattern of deficits specific to schizophrenia or shared with other developmental and psychotic disorders?
Fourthly, are cognitive impairments progressive or static after the onset of psychosis?

Recent research (R. Asarnow et al. 1994, 1995) suggests that children with schizophrenia have specific difficulties with cognitive tasks that make demands on short-term working memory and selective and sustained attention and speed of processing.

These deficits are similar to the deficits reported in adult schizophrenia (Nuechterlain & Dawson 1984; Saykin et al. 1994).

Deficits of attention, short-term and recent long-term memory have also been reported in adolescents with schizophrenia (Friedman et al. 1996). In contrast, well-established 'overlearned' rote language and simple perceptual skills are unimpaired in child and adolescent onset schizophrenia. Asarnow et al. (1991, 1995) have shown that children with schizophrenia have impairments on the span of apprehension task (a target stimulus has to be identified from an array of other figures when displayed for 50 ms). Performance on the task deteriorates markedly when increasing demands are made on information processing capacity (e.g. increasing the number of letters in the display from three to 10). Furthermore, event-related potentials on the span of apprehension task in both children and adults with schizophrenia, compared with age-matched controls, show less negative endogenous activity measured between 100 and 300 ms after the stimulus. Similar findings of reduced event-related potentials have been found during the CPT in both childhood and adult onset schizophrenia (Strandburg et al. 1999). These findings indicate a deficit in the allocation of attentional resources to a stimulus (Strandburg et al. 1994; Asarnow et al. 1995). As with adults, children and adolescents with schizophrenia show high basal autonomic activity and less autonomic responsivity than controls (Gordon et al. 1994), with attenuated increases in skin conductance following the presentation of neutral sounds (Zahn et al. 1997). Childhood onset patients, like adults, show increased reaction times with a loss of ipsimodal advantage compared with healthy controls (Zahn et al. 1998). Abnormalities in smooth pursuit eye movements (SPEM) have also been found in adolescent schizophrenics (mean age 14.5), which suggests continuity with the finding of abnormal SPEM in adult schizophrenics (Iacono & Koenig 1983). Children with schizophrenia also show similar impairments to adult patients on tests of frontal lobe executive function such as the Wisconsin Card Sorting Test (WCST; R. Asarnow et al. 1994).