Abstract
Schizophrenia encompasses a wide variety of cognitive dysfunctions, a number of which can be understood as deficits of inhibition. To date, no research has examined ‘conditioned inhibition’ in schizophrenia - the ability of a stimulus that signals the absence of an expected outcome to counteract the conditioned response produced by a signal for that outcome (a conditioned excitor). A computer-based task was used to measure conditioned excitation and inhibition in the same discrimination procedure, in 25 patients with a confirmed diagnosis of schizophrenia and a community-based comparison sample. Conditioned inhibition was measured by a ratio score, which compared the degree to which the inhibitory stimulus and a neutral control stimulus reduced conditioned responding to the excitatory cue: the lower the ratio, the greater the inhibitory learning. At test the ratios were 0.45 and 0.39 for patient and control groups respectively, and the relevant interaction term of the ANOVA confirmed that the degree of inhibition was reduced in the patient group, with an effect size of r = 0.28.These results demonstrate for the first time that inhibitory learning is impaired in schizophrenia. Such an impairment provides an attractive framework for the interpretation of the positive symptoms of schizophrenia. However, we were unable to demonstrate any relationship between the level of conditioned inhibition and medication. Similarly, in the present study it must be emphasised that the available data did not demonstrate any relationship between individual variation in inhibitory learning and the level of positive symptoms as measured by the PANSS. In fact inhibitory learning impairment was relatively greater in participants with a predominantly negative symptom profile and their excitatory learning was also reduced. Accordingly the next step will be to investigate such relationships in a larger sample with a priori defined sub-groups displaying predominantly positive versus predominantly negative symptoms.
Highlights
Cognitive dysfunction is a definitive aspect of schizophrenia [1,2], and the information-processing abnormalities associated with this condition are diverse
Training stage 1: Excitatory training The results of the initial training stage provided a measure of excitatory learning in the two groups; both groups clearly learned the task, the patient group appeared to respond less on reinforced, and more on nonreinforced trials, than the control participants (Figure 2)
The present study demonstrated that conditioned inhibition (CI) was impaired in schizophrenic compared to matched community control participants
Summary
Cognitive dysfunction is a definitive aspect of schizophrenia [1,2], and the information-processing abnormalities associated with this condition are diverse. It would be simplistic to describe schizophrenia as a deficit in inhibition, because the ‘inhibitory’ processes supposedly affected are very diverse. A disruption in prepulse inhibition [13] - the reduction in the unlearned startle response produced by a weaker version of the later presented startle stimulus - has been reported in schizophrenic populations [11,14,15,16,17,18,19]. There have been reports of a deficit in latent inhibition (LI) [20], which is the slowed acquisition of a learned (or conditioned) response to a conditioned stimulus (CS), which signals a stimulus of intrinsic affective value (an unconditioned stimulus, or US). LI results if the conditioned stimulus is pre-exposed prior to the conditioning treatment [3,9,21,22,23,24]
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