POTENTIATION OF PHOTOTACTIC SUPPRESSION IN HERMISSENDA BY COMPOUND CONDITIONING RESULTS IN POTENTIATED EXCITABILITY CHANGES IN TYPE-B AND TYPE-A PHOTORECEPTORS

Ocular photoreceptor responses were recorded from Hermissenda exposed to compound conditioning, light conditioning, or one of several contro l treatments. Type A photoreceptors from light-conditioned animals res ponded with smaller generator potentials than those from untrained ani mals; type B photoreceptors from light-conditioned animals responded w ith 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 photo receptors, respectively. The same photoresponse changes occurred in ex aggerated form in cells from compound-conditioned animals, but no addi tional input resistance changes were observed. The results suggest tha t potentiation of phototactic suppression by compound conditioning inv olves a facilitation of the same photoreceptor excitability changes pr oduced by mere pairings of light and rotation.