Comparative Neuromechanics

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Terrestrial mammals span a wide range of sizes, with the largest elephant being several million times more massive than the smallest shrew. As a consequence of their size, large and small animals experience very different physical challenges. If an elephant falls, for example, it risks grave injury, while a similar tumble for a shrew would likely be inconsequential. To understand how small and large animals coordinate their movement in the face of differing physical challenges like these, one must first determine how size influences the mechanisms underlying physiological control. The long-term objective of this research program is to understand the scaling of neuromuscular control in terrestrial mammals. Our general hypothesis is that there is a compromise between the responsiveness and resolution of sensorimotor systems that becomes more acute with increases in body size. We recently tested this hypothesis by determining the relationship between body size and maximum nerve conduction velocity. One exciting finding was that from shrews to elephants, the maximum speed at which nerves can conduct information is nearly constant. Consequently, large animals are burdened with relatively long conduction delays. Here we propose to expand on this earlier work to test our general hypothesis as it applies to the latency of spinal reflex pathways and the anatomy of peripheral nerves. We are also proposing to study what we consider the most important implication of these findings - as delays increase in larger animals, they must increasingly depend upon sensorimotor prediction to maintain sensorimotor performance. The general significance of this proposed research is that it will provide fundamental insight into the organization and function of neuromuscular control systems. Effective neuromuscular control is required for many tasks essential to an animal's success including locomotion, feeding and reproduction-an understanding of its scaling promises to provide considerable insight into mammalian behaviour, ecology and evolution.