Potentiation of phototactic suppression in Hermissenda by compound conditioning results in potentiated excitability changes in type B and A photoreceptors.

Ocular photoreceptor responses were recorded from Hermissenda exposed to compound conditioning, light conditioning, or one of several control treatments. Type A photoreceptors from light-conditioned animals responded with smaller generator potentials than those from untrained animals; type B photoreceptors from light-conditioned animals responded with greater generator potentials and action potential frequencies than cells from controls. These photoresponse changes were accompanied by increases and decreases in the input resistances of type B and A photoreceptors, respectively. The same photoresponse changes occurred in exaggerated form in cells from compound-conditioned animals, but no additional input resistance changes were observed. The results suggest that potentiation of phototactic suppression by compound conditioning involves a facilitation of the same photoreceptor excitability changes produced by mere pairings of light and rotation.