The encoding and attentional modulation of perceptual decision in corticocortical circuits

The representation of sensory information in the brain is subject to gain adjustment by attentional processes, such that neural responses to behaviourally relevant or otherwise salient stimuli are enhanced compared to irrelevant or habituated stimuli. The attentional modulation of reward related learning in awake behaving animals is unclear, but there is growing evidence to suggest that dopamine may be a key regulator. Using the rat whiskers as a model system, the project aimed to determine how cortex represents attended stimuli in its coordinated activity in a simple detection task, assessing the role of natural variations in attention. Rats were trained to associate vibrotactile stimuli applied to a single vibrissa with the presentation of a liquid reward. Several deflection amplitudes of 60Hz frequency vibrissa stimulation were investigated around previously identified detection thresholds. During the detection task, neural responses were recorded in single barrel cortex columns and in orbitofrontal cortex using chronically implanted microelectrode arrays. Results suggest that ongoing oscillatory activity before the onset of a weak stimulus has a profound effect on both neural response and behavioural detection. Two further complex conditioning tasks were employed; a paired discrimination and a positive patterning task where tones preceded a vibrotactile stimulation. Optimal psychophysical performance was achieved and serves as a basis for future work to determine the effect of attention on the behavioural and neuronal response to an upcoming tactile stimulation in more complex paradigms. Furthermore, refinements to the head fixed preparation and developments throughout the method were made in order to achieve single unit recordings in midbrain ventral tegmental area and are discussed throughout the thesis. These developments act as a foundation for the method in future work to determine whether dopamine drives the attentional modulation in reward related learning.