Responses of pigeon (Columba livia) Wulst neurons during acquisition and reversal of a visual discrimination task.
The avian visual "Wulst" is a target of the ascending thalamofugal visual pathway. In pigeons (Columba livia), lesion damage to the Wulst has little effect on simple visual discriminations, but impairs performance on tasks such as reversal learning. We recorded the responses of single Wulst neurons as pigeons were trained on the acquisition and subsequent reversal of a visual discrimination. Of the 64 units recorded, 54 (84%) displayed a significant difference in firing rate between some component of the task and the intertrial interval that separated trials. More important, 14 units (22%) displayed a significant change in firing rate exclusively to the S+ and/or S- as learning progressed either during acquisition or reversal. The responses of these 14 neurons indicate that learning during initial acquisition was as likely to correlate with a change in firing rate as during reversal, and some neuronal responses could be characterized as representing reward properties together with visual stimulus features. As such, responses of pigeon Wulst neurons indicate a role in representing aspects of learning as much as the physical/perceptual properties of visual stimuli.