International Journal of Comparative Psychology

Conditioned inhibition (CI) refers to the learned property of a stimulus to predict the absence of an unconditioned stimulus (US). While excitatory forms of conditioning, like alpha conditioning, appear early in metazoan evolution, evidence of true CI in invertebrates remains scant. In the present study, we employed a negative contingency CI training design with an approach/withdrawal test to identify excitatory components involved in CI-like protocols in Caenorhabditis elegans. By using a joint-presentation procedure and alternating stimulus application sites across blocks, we minimised non-associative sensory effects. A control group was added to further consider context-dependent effects. Our results point to learning effects being consistent with excitatory (alpha) conditioning, as trained behavior was facilitated but did not depend on the conditioned stimulus. This underlines the widespread significance of alpha conditioning in invertebrate learning and its contribution to CI-like processes.