Reward, attention and the dorsal noradrenergic bundle.

The resistance to extinction seen after lesion to the dorsal noradrenergic bundle has been suggested to arise from a deficit in internal inhibition or a 'perseverative' type of deficit. This hypothesis is tested by examining the ability of 6-hydroxydopamine-treated animals to inhibit a previously developed preference for saccharine solution as a result of poisoning with lithium chloride. Unimpaired taste aversion is found, arguing against a deficit in the ability to inhibit a prepotent response. An alternative explanation of the dorsal bundle extinction effect (DBEE), that of alterations in attention, is tested by acquisition and reversal of a successive light-dark discrimination. Both acquisition and reversal are severely impaired, suggesting that the treated animals have difficulty in attending to a specific stimulus in the environment when this is required in order to structure behaviour appropriately, and thus being consistent with a role for the dorsal bundle in the control of attentional processes.