Differential Performance of Acute and Chronic Schizophrenics in a Latent Inhibition Task

Abstract

Differences between acute (N = 26) and chronic (N = 27) schizophrenics diagnosed by Research Diagnostic Criteria and normal controls (N = 53) were examined in a task measuring latent inhibition, i.e., the retardation of learning that normally occurs when a subject forms an association to a stimulus previously repeatedly presented without consequence. In rats, latent inhibition would be similarly disrupted in acute schizophrenics (presumably in a hyperdopaminergic state) but not in chronic, medicated schizophrenics. Each group was subdivided and assigned randomly to two experimental conditions, preexposure or non-preexposure. Preexposed subjects first heard 30 bursts of white noise through headphones while monitoring a lists of nonsense syllables; non-preexpossed subjects listened to the nonsense syllables without the white noise. Subjects in both conditions were then given the opportunity to learn that the noise signalled increments in a visually displayed number. Preexposed normals and chronic schizophrenics learned this association more slowly than non-preexposed subjects (latent inhibition); as predicted, acute schizophrenics failed to display this effect. After 6 to 7 weeks, 11 acute and 13 chronic patients were retested; both groups now showed latent inhibition. These results are discussed in relation to the dopamine hypothesis of schizophrenia.