Value coding in the pigeon nidopallium caudolaterale

Abstract

Until recently, the avian brain has remained relatively unexplored by neuroscientists. However, as reports of evidence of high-order behaviour in birds has increased, the avian brain is increasingly becoming a model of interest to the field. Despite the evolutionary trajectory diverging millions of years ago, some structural similarities have been highlighted that have prompted further research into the brain and behaviour of pigeons. One such area is the nidopallium caudolaterale (NCL) which is the structural homologue of the mammalian prefrontal cortex (PFC). The aim of the current thesis was to explore the similarities in the activity of NCL cells compared to those reported in the mammalian PFC. In particular, we explored the extent to which NCL cells exhibit value coding when different factors were manipulated. Pigeons were trained to associate stimuli with different outcomes, where the value of a reward was discounted by a preceding cost. The value manipulations used in the experiments conducted were increasing the delay to the reward, increasing the physical, and the cognitive effort required to attain a reward, and the probability of receiving a reward. We recorded from cells in the NCL and found evidence of value coding in relation to delay discounting, and physical effort discounting, suggesting similar properties to cells found in the mammalian orbitofrontal cortex, and anterior cingulate cortex. Our pursuit of an appropriate cognitive effort task fell short, and as such, no conclusions could be drawn as to whether NCL encodes cognitive effort discounting. In the final experiment, where probability discounting was manipulated, NCL cells showed no differences in firing to suggest that the area is involved in encoding probabilistic discounting. In summary, the studies in the current thesis add to the literature comparing the functional characteristics of the pigeon NCL to the mammalian PFC, and identify areas for further research around the question of cognitive effort discounting in animals, and how the avian brain processes probability.