Abstract
Objective: The objective was to outline the development of the concept of allusive thinking as a genetic marker of predisposition to schizophrenia and relate this to other cognitive markers of this predisposition.
Method: Publications were reviewed which were considered relevant to the objective.
Results: Allusive thinking as detected clinically could be measured objectively from subjects' performance on an Object Sorting Test. Using this test it was shown that parents, both of patients with schizophrenia and of university students with allusive thinking, themselves showed allusive thinking, indicating it was familially transmitted. Subjects with allusive thinking showed reduced cortical evoked brain P300 potentials, suggesting the transmission was genetic. The hypothesis that allusive thinking was associated with weaker cortical inhibitory processes was supported by the finding that subjects with such thinking chose more remote word associations. It was sug-gested that reasons allusive thinking has not been used as a marker in intervention studies is that as a dimension of abstract thinking, marked allusive thinking is not associated with a high risk of developing schizophrenia, and that administration of the Object Sorting Test is time-consuming. Other dimensional cognitive factors, such as psychoticism and perceptual anhedonia and aberration, are independent of allusive thinking and are also associated with a low risk of developing schizophrenia. Genetic transmission of schizophrenia would appear to involve a number of predisposing factors distributed dimensionally in the population with the contribution of each factor being small.
Conclusions: As they are associated with only a low risk of predisposition to schizo-phrenia, cognitive markers may not be of immediate value in the prevention of schiz-ophrenia when compared with the less specific markers used for this purpose. However, it would seem that their study will be necessary if the nature of the genetic transmission of the illness is to be understood. This understanding could be expected to ultimately lead to more effective prevention.