Research

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Neuroscientists employ a device attached to the leg of Lucy, an Asian elephant at the Edmonton zoo, to measure her muscle activity. SFU kinesiology professor Max Donelan and doctoral student Heather More’s most recent research may explain why bigger animals such as Lucy are slower—and frequently smarter—than smaller animals.

Nature’s speed limit?

July 8, 2010

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According to new SFU research, there’s a speed limit on the information super-highways that route key messages through animal nervous systems. And while that limit may make larger mammals slower than smaller animals, it could also make them smarter.

Biomedical physiology and kinesiology professor Max Donelan and grad student Heather More led the study, published online in the Proceedings of the Royal Society B on June 30.

They found that land mammals’ nervous systems conduct information at a maximum speed relatively constant regardless of the animal’s size. That helps explain why larger animals such as elephants are slow and awkward, while mice are quick and agile.

"The size of an animal’s nerve is dependent on the number and diameter of nerve fibres it contains," says Donelan. "The speed at which each nerve fibre can conduct signals depends on its diameter, with larger-diameter fibres able to transmit information faster.

"If a nerve has more fibres, the animal can have a higher density of sensory receptors to respond to its environment more precisely. But since nerves cannot be infinitely large there is a compromise necessary between the number and size of fibres in a nerve."

Explains More: "Larger animals experience much longer delays in sensing stimuli and initiating movement. As body size increases, animals must trade off the ability to conduct information quickly with the ability to precisely sense and respond to the environment."

Since large animals cannot speed up their nerve impulses, they must slow down their movements to compensate for the delayed transfer of information. This is further evidence, notes Donelan, that dinosaurs could not have been both large and nimble.

"We think larger animals need to think ahead and predict any changes that will occur so they have time to adapt their movements accordingly," says Donelan. "That’s what we want to study next."

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