Abstract
Schizophrenia is a major neurodevelopmental disorder that affects approximately 1% of the population. In New Zealand this means that around 30,000-45,000 individuals are affected (Murray, 1996). Individuals diagnosed with schizophrenia have a mortality rate of 2.5% higher than individuals without schizophrenia. This includes a suicide rate of 10-15% among individuals with schizophrenia (Masters, 1997).
While the positive symptoms (i.e. hallucinations and delusions), and the psychoses brought on by these symptoms are the most prototypical of schizophrenia, the functional impairments produced by the cognitive and motivational deficits are more likely to impact the patient’s quality of life (Bowie & Harvey, 2006). One aspect of dysfunctional cognition-motivation interaction manifests itself as an inability to change behaviour adaptively in response to motivationally significant cues (Gold et al., 2012). This interaction could contribute to the reason why current treatments of schizophrenia that are aimed at improving cognition alone produce no lasting recovery from behavioural deficits (Medalia & Choi, 2009).
While the biological basis of both cognition and motivation have been widely studied, the neural circuitry underlying the interaction of cognition and motivation is relatively unknown. One area of this interaction that could have particularly dramatic consequences if gone wrong is the interaction between attention and motivation. This is because attention directly relates to cognitive flexibility in different situations (Peltz et al., 2011). Because attention modulates other cognitive processes, the impairment observed in attention, particularly the motivated recruitment of attention in response to reward-related cues, has devastating effects on the cognitive processing and adaptive behaviour of individuals with schizophrenia (Cornblatt & Malhotra, 2001).
The 5-Choice Serial Reaction Time Task (5-CSRTT) was developed as a way to understand the nature of attention deficits shown by children with attention-deficit hyperactivity disorder (ADHD) (Robbins, 2002). The task tests the ability of the rat to sustain attention divided among a number of locations over a large number of trials (about 100). This capacity is measured by the accuracy of reporting the stimuli; the choice or response accuracy measure is simply the proportion of correct responses over total given responses. The 5-CSRTT assesses several aspects of attention, including sustained attention and cue detection, and relies upon regular frontal lobe, specifically prefrontal cortex, function (Robbins, 2002). The task used in the current study is a modified version of 5CSRTT, created to specifically assay the interaction between attention and motivation. The current study uses the operant paradigm called the Signalled-Probability Sustained Attention (SPSA) task. The SPSA task was specifically design to assay the interaction between attention and modulation, and has a signalled probability component, where at the beginning of the trial the house light being on or off signifies if the trial is going to have a high or low probability of reward. The rest of the trial is composed of a two-lever operant discrimination task, where a cue light being illuminated indicates which lever the subject is required to press for a correct response.
The current study was designed to determine the neural circuits that are involved in cognition-motivation interactions. It was hypothesised that signalling the probability of reward would result in behavioural differences in responding during trials, such that accuracy would be higher on high probability trials than on low probability trials. Also, these differences would be accompanied by the activation of, and communication between, nucleus accumbens-prelimbic cortex. The SPSA paradigm was used to assess the motivated recruitment of attention in response to reward-related cues. Simultaneous electrophysiological recordings from the nucleus accumbens (Nacc) and the prelimbic cortex (PrL) during the acquisition of the SPSA task were used to determine activity and connectivity relating to motivational and attentional processes.