Risk of adult schizophrenia and its relationship to childhood IQ in the 1958 British birth cohort.

BACKGROUND: An inverse relationship between risk of schizophrenia and premorbid IQ is a robust empirical finding. Cognitive impairment may be a core feature of schizophrenia in addition to the clinical symptoms that have historically defined the disorder. AIMS: To evaluate whether risk of schizophrenia increases linearly or nonlinearly with the lowering of premorbid IQ after adjustment for a range of confounding factors. METHODS: IQ data from the 1958 National Child Development Study, a prospective national birth cohort (n = 17 419), were linked with psychiatric admissions in England and Wales over a 20-year period. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition diagnoses were derived from case notes. RESULTS: A clear nonlinear inverse relationship between general intelligence at ages 7 and 11 and risk of adult psychosis was found even after adjustment for potential social, behavioral, or demographic confounding factors. No such relationship was found for affective disorders. CONCLUSIONS: The nonlinear relationship suggests an excess risk of schizophrenia in children with premorbid IQ in the learning disabilities range. Previous reports of a linear relationship are likely to be a result of less sensitive statistical methods for detecting nonlinearity.

Pragmatic use of language by children who develop schizophrenia in adult life.

At eleven years of age all children in a UK national birth cohort wrote short stories about the life they expected to be leading at age 25. Using a data linkage exercise, we identified those who later developed schizophrenia, affective psychosis, or other non-psychotic psychiatric disorders in later life based on the PSE CATEGO diagnostic system. The majority of these had completed the written essays. Controls from the reference population were selected, matched for gender, IQ and social and economic status. The essays were scored using well established methods for assessing pragmatic use of language, namely narrative coherence and linguistic cohesion. We hypothesised that children pre-morbid for schizophrenia (Pre-Scz) would obtain low scores on all these measures. However this general hypothesis was largely disproved by the data, although some unpredicted gender effects were found. It is concluded that thought is organised in an unexceptional way in adolescents before they develop schizophrenia, once the data are corrected for any lowering of general cognitive ability in the Pre-Scz cases.

Overinclusive thought and loosening of associations are not unique to schizophrenia and are produced in Alzheimer's dementia.

INTRODUCTION: Bleuler's concept of loosening of associations which he believed epitomised psychotic thinking can manifest as overinclusion (merging of semantic categories) on semantic categorisation tasks. Overinclusion is explained by excessive activation within the semantic memory network to subordinate features with low associative strength. Therefore patients with degradation of subordinate semantic knowledge (e.g., with Alzheimer's Dementia-AD) should not produce overinclusion errors. METHODS: 22 people with schizophrenia and 26 people with AD (nonpsychotic, semantic memory impairment) were compared on a semantic categorisation test, the Category Generation Test (CGT). The CGT involves free-sorting 45 cards of pictured objects from five taxonomic groups (e.g., animals). Overinclusion and underinclusion (subdivision of categories) errors were recorded and the strategies used in generating these abnormal categories were explored qualitatively. RESULTS: Two-thirds of both groups generated abnormal categories, including frequent overinclusions. Using a semantic probes test, abnormal categorisations could not be attributed to knowledge degradation as this appeared preserved. Qualitatively, the two groups differed in their sorting strategies. CONCLUSIONS: Loosening of associations is found in nonpsychotic people, who have semantic memory impairments (e.g., AD), using semantic knowledge tasks. However there may be different explanations; atypical semantic categorisation in schizophrenia appears to result from attention to thematic rather than feature-based associations.

Evidence for a dissociation of structural and semantic knowledge in dementia of the Alzheimer type (DAT).

Object recognition and naming deficits in dementia of the Alzheimer type (DAT) have typically been attributed to deficits in semantic processing, with only a few studies proposing loci of deficits other than semantic. One possible cause of DAT object recognition impairments could involve deficits in processing structural aspects of visually presented items. In this paper, we assess the performance of a group of mild DAT patients on two tasks of structural access, object decision, and the complete/incomplete task (based on part-whole matching task), as well as on a semantic probes task, designed to assess the patients' semantic knowledge of the same items for which structural knowledge had earlier been assessed. The DAT patients were substantially impaired in their performance on tasks of structural access. Further, no evidence for item-to-item consistency in the DAT patients' errors for the structural and semantic tasks was found, raising the possibility that structural and semantic knowledge may become differentially impaired in DAT.

Loss of high-level perceptual knowledge of object structure in DAT.

Visual object recognition and naming deficits in patients with dementia of the Alzheimer type (DAT) have typically been attributed to deficits in semantic processing. On a visual object naming test, a group of 10 mild, early stage DAT patients (mean MMSE=23.8) were found to suffer from anomia, compared to a group of 10 age-matched control participants. DAT naming errors were typically within category (commission), associative or circumlocutory errors. Performance on tests of low level visuo-spatial ability fell within the normal range. Together these results suggested that anomia resulted from a dysfunctional semantic system with intact visual perception. However, in a naming task using visually degraded images of familiar objects, the recognition threshold in DAT patients was significantly higher, indicating the need for a more visually complete object representation, before it could be accurately recognised. In a matched task using words visually degraded in an identical manner, the recognition threshold for DAT patients was very similar to that of the control group. It is argued that these results support the idea that impaired structural descriptions of objects (i.e., pre-semantic representation of an object within the visual perceptual system) combines with degraded semantic representations to produce anomia in mild early stage DAT.

Analogical reasoning in schizophrenic delusions.

PURPOSE: Reasoning ability has often been argued to be impaired in people with schizophrenic delusions, although evidence for this is far from convincing. This experiment examined the analogical reasoning abilities of several groups of patients, including non-deluded and deluded schizophrenics, to test the hypothesis that performance by the deluded schizophrenic group would be impaired. SUBJECTS/MATERIALS: Eleven deluded schizophrenics, 10 depressed subjects, seven non-deluded schizophrenics and 16 matched non-psychiatric controls, who were matched on a number of key variables, were asked to solve an analogical reasoning task. RESULTS: Performance by the deluded schizophrenic group was certainly impaired when compared with the depressed and non-psychiatric control groups though less convincingly so when compared with the non-deluded schizophrenic group. The impairment shown by the deluded schizophrenic group seemed to occur at the initial stage of the reasoning task. DISCUSSION: The particular type of impairment shown by the deluded subjects was assessed in relation to other cognitive problems already researched and the implications of these problems on reasoning tasks and theories of delusions was discussed.

Elasticity and confabulation in schizophrenic delusions.

BACKGROUND: This experiment examines two aspects of delusional cognition that have been reported clinically but not investigated empirically. These are the incorporation of potentially conflicting information into the recall of delusion-related scripts and the type and amount of material produced additional to that presented for recall, referred to here as confabulation. METHODS: Three groups of patients--deluded schizophrenics, non-deluded schizophrenics and matched non-psychiatric controls--were asked to recall two 15-item scripts, which comprised 10 typical and five atypical components. It was hypothesized that deluded subjects whose delusion was relevant to one of the scripts would recall more of the atypical components of the script and would also be less likely to make script-atypical confabulations in the recall of this particular script. RESULTS: Recall was assessed for the amount and type of content remembered and the amount and type of confabulation. The results did not support the hypothesis that atypical items would be incorporated into the recall of delusion-relevant material. However, deluded subjects did retain their schema boundaries in the recall of script items relevant to their own delusion but were less able to adhere to a script framework in the recall of material unrelated to their delusion. CONCLUSIONS: These results are discussed within a schema specific account of delusions, which conceptualizes the delusion as an overused schema whose preferential use leads to a failure to develop other scripts but whose own contents remain well-defined.