Social decision-making: the effects of schizophrenia, ketamine and oxytocin

The primary focus of this thesis is the investigation of social dysfunction and decision-making deficits in schizophrenia. To this end, a task was devised which incorporated face stimuli into a decision-making task. This allowed me to determine how the presence of emotional faces affects decision-making behaviour. This task was imaged in healthy controls, and I found that controls were biased towards the selection of smiling faces. By modelling subject behaviour, I showed that brain areas associated with theory of mind showed activity corresponding to this bias. In patients with schizophrenia, I found that this bias was exaggerated such that patients were significantly less likely to select an angry face even when it was the optimum choice in the context of the task. However, accuracy was no different to controls. Using an emotion recognition task, I also found corresponding evidence that angry faces are processed differently in schizophrenia. I then investigated effects of the hormone oxytocin (OT) in healthy controls. Oxytocin has been shown to increase trust and generosity and is therefore thought to promote prosocial behaviours. In controls, I found that OT lessened aversion to angry faces, suggesting that OT could potentially normalise the heightened aversion seen in patients. However, since patients seem to process angry faces differently, OT effects in controls might not be generalisable. I went on to further test patients decision making ability and showed that patients tend to ‘jump to conclusions’ in the classic beads task, and are furthermore impaired at learning a sequence of button presses from noisy feedback. This suggests that decision making impairments in schizophrenia are strongly contingent on task demands, since no accuracy deficit was seen in the face decision task. This suggests that gradual acquisition of probabilistic relationships may be preserved. Impaired decision making seems to manifest only under certain experimental conditions, and various factors are critical to this. I also investigated whether the anaesthetic ketamine (which has been proposed as a possible model of psychosis) could replicate these decision making deficits. I could find no evidence that ketamine could model this aspect of behaviour. This suggests that ketamine models of schizophrenia may not be applicable to decision making