Parameters of the dorsal bundle extinction effect: previous extinction experience.

Lesion to the dorsal noradrenergic bundle using the selective neurotoxin 6-hydroxydopamine which depleted telencephalic noradrenaline to less than 5% of control values was found to cause prolonged responding in extinction of a continuously reinforced (CRF) operant lever pressing response (a further replication of the dorsal bundle extinction effect). The parameters involved in causing this effect). The parameters involved in causing this effect were investigated, particularly the role of previous extinction experience. Although resistance to extinction was seen the first time animals were placed in extinction, it disappeared when they were retrained on CRF and extinguished a second time. Experience of extinction as part of the acquisition process, brought about by training on a successive visual discrimination, also prevented the development of over-responding in subsequent extinction. These results are discussed in the context of related demonstrations of the absence of the dorsal bundle extinction effect after partially reinforced acquistion training.