Cross-modality sensory integration in the control of feeding in Aplysia

Abstract

Cross-modality sensory integration controlling feeding in the marine mollusc Aplysia was examined by dissociating chemical and tactile components of seaweed stimuli which evoke biting responses. The chemical stimuli were graded concentrations of seaweed extract perfused over the tentacles and lips of the animals. The tactile stimulus was a glass probe applied to these same structures. Tactile stimuli were found to be ineffective in evoking repeated biting responses, whereas chemical stimuli evoked repeated though irregular responses. Combined chemical and tactile stimuli evoked regular biting. Mean interresponse intervals for combined stimuli were significantly less than those measured for chemical or tactile stimuli alone. When the concentration of the chemical stimulus was systematically varied, the addition of a tactile stimulus shifted the function relating chemostimulus strength to biting frequency toward greater responsiveness. The results suggest that cross-modality sensory integration provides Aplysia with feature detection capabilities which enhance the ability of the animal to detect appropriate food objects in the environment.