ABSTRACT
The associative learning phenomenon termed ‘blocking’ demonstrates that animals do not necessarily associate a conditioned stimulus (e.g. X) with reinforcement if X is coincident with a second conditioned stimulus (e.g. A) that had already been associated with the same reinforcement. Blocking therefore represents a tactic that animals can use to modulate associative learning in order to focus on the most predictive stimuli at the expense of novel ones. Using an olfactory blocking paradigm in the honeybee, we investigated the mechanistic basis for olfactory blocking. We show that removing input from one antenna eliminates the blocking of one odor by another. Since antennal sensory neurons only project to the ipsilateral antennal lobe in the honeybee, more central processing regions of the brain than the antennae must be crucial for establishing blocking. Further experiments show that this bilateral interaction between brain hemispheres is crucial during both the induction and the expression of blocking. This result implies that blocking involves an active inhibition of odor association and recall, and that this inhibition is mediated by a structure that spans both brain hemispheres. This interpretation is consistent with a role for identified bilateral modulatory neurons in the production of blocking.
