The computational neurobiology of attention. (360G-Wellcome-089264_Z_09_Z)

1. Work up a plausible model of behaviour in the task, based on the Free Energy Principle and informed by knowledge of cortical structure and neurotransmitter action. 2. Acquire performance and neuroimaging data in the task from normal subjects. Use these data to parameterise and optimize the model, using Bayesian model comparison. 3. Choose one or two psychoactive drugs that are implicated in mental disorder and abnormal task performance in normal subjects and measure performance on this task under these drugs. I will then re-parameterise the model for performance on this drug. The PhD will focus on attention. Patients with schizophrenia seem to be particularly deficient in attentional tasks which involve conflict or identifying which stimulus to attend to (Luck & Gold, 2008; Wang et al., 2005; Maruff et al., 1998). Thus, I will use a modified version of the Posner task (Posner et al., 1978), which introduces conflict, to study this phenomenon. In the Posner subjects are required to foveate a central spot and respond as quickly as possible to the appearance of a peripheral target. The side the target will appear is cued at a fixed interval beforehand. The cue is correct (valid) 80% of the time. Posner found that reaction times to validly cued targets were significantly shorter than to targets which were incorrectly cued. This demonstrated that attention could be moved to salient locations in the absence of gaze shift. Evidence as to the performance of schizophrenic patients in this task is mixed. The choice of this paradigm is based partly on the fact that the groundwork of the modelling has already been done. Moreover, the Posner paradigm yields a wealth of data ? the values parameterising the reaction time distributions to cues with up to three different levels of validity, plus the proportion of correct responses ? which will furnish empirical constraints on key model parameters (e.g., synaptic rate constants and gain). In addition, the cognitive processes engaged by this paradigm are clearly influenced by the pathological process underlying schizophrenia.