The individual cells responsible for responding to sensory inputs–the strong scent of a flower, the light touch of a spring breeze–can cope with only a small amount of input. Yet the human ear can hear and process sounds ranging from a pin drop to the roar of a jet engine. Scientists have struggled to account for how this individually narrow range combines in a network to produce the wide range of sensed experience. Now physicists have shown how the mathematical models that describe phase transitions in physical systems might also explain our capacity to hear, see, smell, taste and touch.
Mauro Copelli and Osame Kinouchi of the University of Sao Paulo in Brazil used a mathematical formula to show how a random network of “excitable elements,” such as neurons or axons, have a collective response that is both exquisitely sensitive and broad in scope. When subtle stimuli hit the network, sensitivity is improved because of the ability of one neuron to excite its neighbor. When strong stimuli hit the network, the response is similarly strong, following what are known as power laws–mathematical relationships that do not vary with scale.