Visual_IR2.jpg (12786 bytes)  Visual Image (left), Infrared image (right)

Rattlesnakes may shift between visual (eyes) and infrared (facial pits) stimuli without significant loss of predatory performance during an envenomating strike. The relative equivalency of these proximate stimuli is correlated with the organization of the associated neural pathways in the central nervous system. Visual and infrared information, although gathered by different sensory organs, converge within the optic tectum in an orderly spatiotopical representation where bimodal neurons respond to both stimuli. In turn, the tectum sends efferent pathways directly to premotor (brainstem) and indirectly to motor areas (spinal cord) where axial muscles involved in the strike might be activated.

On the other hand, rattlesnakes do not maintain a high level of equivalent predatory performance when switching between chemosensory stimuli, olfactory and vomeronasal (VNO) information. Deprived of vomeronasal input, strikes drop by about half, and poststrike trailing is lost entirely. Surprisingly, compensation by switching to information delivered via an intact olfactory input does not occur, despite the convergence of chemosensory information within the central nervous system.

Finally, the launch of a targeted, envenomating strike involves both these modalities, radiation reception (visual, infrared) and chemoreception (olfactory, vomeronasal). However, in the absence of chemosensory information (VNO), the radiation modalities do not completely compensate nor maintain a high level of predatory performance. Conversely, in the absence of radiation information, the chemosensory modalities do not completely compensate nor maintain a high level of predatory performance. This absence of compensation in this multimodal system is also correlated with an absence of convergence of radiation and chemical information in the central nervous system.

See: Kardong, K. V. and H. Berkhoudt. 1998. Rattlesnake Hunting Behavior: Correlations Between Plasticity of Predatory Performance and Neuroanatomy. Brain, Behavior, Evolution.

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