A Universal Law of Sensory Adaptation

Abstract Sensory adaptation is the gradual decline in response as recorded from sensory neurons to a constant stimulus. Measuring adaptation involves counting the time-varying rate of action potentials generated by the sensory neuron. A typical adaptation curve will involve spontaneous activity prior to the introduction of the stimulus, a peak level of activity soon after the stimulus is presented, and a gradual fall to a new steady-state value. In this study, the steady-state activity is shown to be equal to the geometric mean of the spontaneous and peak activities. This remarkably simple equation holds across different sensory modalities and in different animal species. It is obeyed in both modern measurements of neural adaptation as well as the original recordings of Lord Adrian in his seminal work on the discovery of the all-or-nothing principle of nerves. It is likely a universal relationship governing the peripheral response of sensory neurons.