Delay activity in the Wulst of pigeons (Columba livia) displays neural correlates for both memory and reward.

Abstract

The avian brain has two main visual pathways: the tectofugal pathway, that terminates in the Entopallium, and the thalamofugal pathway, that terminates in the avian Wulst. The Wulst is a parasagittal bulge located on the avian telencephalon, and is considered to be homologous to mammalian Striate cortex. Previous electrophysiology studies of the avian visual system have only recorded from the Entopallium, in which neurons displayed evidence of sample coding. We recorded single-unit activity from the Wulst of four birds trained on a delayed matching-to-sample (DMS) procedure. Two birds were trained and tested with differential outcomes (DO), in which only one sample stimulus was rewarded for a correct response; and two birds were trained and tested with common outcomes (CO), where both sample stimuli were rewarded. We expected delay activity from the Wulst would differ from baseline activity for both stimuli, and across both types of DMS task. For the CO DMS task, we found that excitatory and inhibitory delay activity differed from baseline activity following both sample stimuli. However, for the DO DMS task, we found inhibitory delay activity deviated from baseline activity following both rewarded and unrewarded sample stimuli. Whereas, excitatory delay activity only differed from baseline following the rewarded sample stimulus, and not the unrewarded stimulus. From this, it appears that the avian Wulst may be involved in both memory and reward coding.