Abstract
Attention is the ability to process incoming stimuli from the environment and direct the desirable behaviour accordingly. Sustained attention is the ability to maintain readiness and repeatedly react to the environment for lengthy periods of time. To maintain performance over time, the demand on sustained attention increases, thus the levels of reward must also increase to meet the level of motivation required. Motivation processes encode reward incentives and guides behaviour based on salience of rewards. Reward salience can be directly linked to attentional performance, by increasing the reward attentional performance can be increased.
The basal forebrain (BF) and the nucleus accumbens (NAc) are both involved in a complex circuit involving direct and indirect bidirectional exchange of information between regions. The BF has been identified as a major relay station for processing sensory information and as such has been strongly linked to aspects of attention and motivation, such as cue detection and encoding of reward salience. The NAc plays an important role as an interface between limbic and motor systems and as such has been linked to encoding of reward incentives and guiding goal directed behaviour.
To establish neural interactions between the BF and NAc during the processes of motivational modulation of sustained attention, the current set of experiments was proposed. The first experiment included recording local field potentials (LFP) simultaneously from both the BF and NAc during a signalled probability sustained attention (SPSA) task. This task involved two types of trials related to the reward probability available, high reward probability trials (100% probability for correct response) and low reward probability trials (10% probability for a correct response). Subjects then attended to a lever cue indicating which, out of two, levers to press to potentially gain a reward, which was dependent on the trial type. There were an evenly distributed number of each trial type within a session and rats performed 20 sessions to reliable acquire the task. The second experiment incorporated single unit recordings of neurons within the BF during the SPSA task. Through these experiments, we revealed that BF and NAc activity increases in higher reward salient conditions encoding motivation but only the BF showed increased activation during cue detection following a varied delay. Coherence was increased between the two regions when incorrect responses produced no reward, indicating a potential mechanism for encoding prediction errors. To further understand the interactions between the BF and NAc granger causality analysis was also performed, revealing there was greater BF to NAc granger causality during post error response in high reward probability trials. This indicates that BF activation has a stronger predictability of future NAc activation, thus supporting a potential mechanism for prediction error processing. Hence, these results confirmed the roles these regions have in motivation and attention.