Effects of pre-exposure and post-exposure of the context in habituation of the retraction response in earthworms (Lumbricidae)

The context specificity of habituation has been demonstrated in earthworms. After the habituation of the retraction response to a light, a recovery of the response was observed when subjects are re-habituated in a different context. Some theories assume that an association between the context and the unconditioned stimulus could underlie this result. A series of experiments were conducted in order to test this issue. We assessed the potential disruptive effects of post-exposure (extinction effect) and pre-exposure of the context (latent inhibition effect) on the establishment of a context-US association. A recovery of response during subsequent rehabituation test was expected. The results of Experiment 1 showed that the extinction was effective, the post-exposure of the context after habituation produced a recovery of the retraction response. This result was replicated in Experiment 2 where the post-exposure condition was compared with a pre-exposure one. However, the pre-exposure to the context did not result in a recovery of the response in the rehabituation test, but also produced a general decrement on the response during the habituation training, that it has been interpreted as decrement in context's salience. In summary, these results suggest the involvement of associative and nonassociative processes in habituation learning.