Strength of conditioning determines the effects of septo-hippocampal lesions on taste aversion learning

Abstract

Several authors have argued that the formation of conditioned flavor aversions (bait-shyness) is qualitatively different than the formation of associations between exteroceptive cues and external noxious reinforcers. Furthermore, it is argued that these two presumably distinct forms of learning are dependent on different neural substrates. This contention is strengthened by several recent reports that lesions of the septum or hippocampus that disrupt locomotor passive avoidance learning do not impair baitshyness, even though taste aversion studies typically use a passive avoidance paradigm. Nevertheless, other studies have reported significant taste aversion deficits after septal or hippocampal lesions. In the present study, we suggest that the primary factor that determines whether septo-hippocampal lesions impair taste aversion learning is the strength of the conditioning method employed. Experiment 1 showed that large lesions of the septum, the fimbria-fornix, or the dorsal hippocampus did not impair a flavor aversion learned with a strong conditioning paradigm. In contrast, both septal and hippocampal lesions disrupted a flavor aversion learned with the weaker conditioning method of Experiment 2. We conclude that it is not yet possible to state that the association of flavor cues with interoceptive events depends on neural circuits different from those involved in the association of exteroceptive cues and events.