Rattlesnake hunting behavior: Correlations between plasticity of predatoryperformance and neuroanatomy

Rattlesnakes may shift between visual (eyes) and infrared (facial pits) sti muli without significant loss of predatory performance during an envenomati ng strike. The relative equivalency of these proximate stimuli is correlate d with the organization of the associated neural pathways in the central ne rvous system. Visual and infrared information, although gathered by differe nt sensory organs, converges within the optic tectum in an orderly spatioto pical representation where bimodal neurons respond to both stimuli. In turn , the tectum sends efferent pathways directly to premotor areas (brainstem) and indirectly to motor areas (spinal cord) where axial muscles involved i n the strike might be activated. On the other hand, rattlesnakes do not mai ntain a high level of equivalent predatory performance when switching betwe en chemosensory stimuli i.e., olfactory, and vomeronasal information. Depri ved of vomeronasal input, strikes drop by about half, and poststrike traili ng is lost entirely. Surprisingly, compensation by switching to information delivered via an intact olfactory input does not occur, despite the conver gence of chemosensory information within the central nervous system. Finall y, the launch of a targeted, envenomating strike involves both these modali ties: radiation reception (visual, infrared) and chemoreception (olfactory, vomeronasal). However, in the absence of chemosensory information, the rad iation modalities do not completely compensate, nor does the animal maintai n a high level of predatory performance. Similarly, in the absence of radia tion information, the chemosensory modalities do not completely compensate, nor does the animal maintain a high level of predatory performance. The ab sence of compensation in this multimodal system is also correlated with an absence of convergence of radiation and chemical information, at least at t he level of first and second-order neurons, in the central nervous system.