Do patients with schizophrenia exhibit aberrant salience?

Abstract

Background: It has been suggested that some psychotic symptoms reflect 'aberrant salience', related to dysfunctional reward learning. To test this hypothesis we investigated whether patients with schizophrenia showed impaired learning of task-relevant stimulus-reinforcement associations in the presence of distracting task-irrelevant cues.

Method: We tested 20 medicated patients with schizophrenia and 17 controls on a reaction time game, the Salience Attribution Test. In this game, participants made a speeded response to earn money in the presence of conditioned stimuli (CSs). Each CS comprised two visual dimensions, colour and form. Probability of reinforcement varied over one of these dimensions (task-relevant), but not the other (task-irrelevant). Measures of adaptive and aberrant motivational salience were calculated on the basis of latency and subjective reinforcement probability rating differences over the task-relevant and task-irrelevant dimensions respectively.

Results: Participants rated reinforcement significantly more likely and responded significantly faster on high-probability-reinforced relative to low-probability-reinforced trials, representing adaptive motivational salience. Patients exhibited reduced adaptive salience relative to controls, but the two groups did not differ in terms of aberrant salience. Patients with delusions exhibited significantly greater aberrant salience than those without delusions, and aberrant salience also correlated with negative symptoms. In the controls, aberrant salience correlated significantly with 'introvertive anhedonia' schizotypy.

Conclusions: These data support the hypothesis that aberrant salience is related to the presence of delusions in medicated patients with schizophrenia, but are also suggestive of a link with negative symptoms. The relationship between aberrant salience and psychotic symptoms warrants further investigation in unmedicated patients.

Fig. 1

The Salience Attribution Test. Participants were required to respond to the black square as quickly as possible. On 50% of trials, participants won more money for quicker responses. The conditioned stimuli appearing before the response are coloured either red or blue.

Fig. 2

Adaptive salience based on latency in patients with schizophrenia and controls. * Patients exhibited reduced adaptive salience relative to controls (p=0.035). Values are means and standard errors.

Fig. 3

Adaptive salience based on subjective reinforcement probability ratings in patients with schizophrenia and controls. * Patients exhibited reduced adaptive salience relative to controls (p=0.002). Values are means and standard errors.

Fig. 4

Aberrant salience calculated from subjective reinforcement probability ratings in patients with schizophrenia. * Patients with delusions exhibited significantly greater aberrant salience than those without delusions (p=0.005). Values are means and standard errors.

Fig. 5

Relationship between the sum of global scores from the Scale for the Assessment of Negative Symptoms (SANS) and aberrant salience (calculated from subjective reinforcement probability ratings). Aberrant salience correlated significantly with negative symptoms in patients with schizophrenia (r=0.51, p=0.020).