Conditioned drinking as avoidance learning.

Blocking the robust conditioned drinking response following conditioning eliminates the isotonic procaine conditioned response (CR) but not the hypertonic procaine CR. Rats allowed to drink in the box during conditioning form a larger CR than rats merely injected with hypertonic or isotonic procain who are prevented from drinking in the box: response blocking during extinction eliminated if no experience of drinking water in the box occurs either during baseline or during conditioning. Blocking the drinking response, like blocking shock avoidance, markedly reduces its high resistance to extinction. This suggests that rats overdrink to avoid anticipated illness, and fail to extinguish partially because they are never exposed to the fact that no illness will occur even if no drinking occurs.