Adaptation and sensory coding

Abstract

Adrian’s seminal work of 1926 (Adrian and Zotterman, 1926a, b) demonstrated three fundamental principles of neural coding. First, the elementary symbol of the neural code is the all-or-none ste-reotypical action potential. Second, there is a quantitative relationship between stimulus parameters and the magnitude of the neural response: for example, a more intense load on a muscle stretch receptor elicits more action potentials. Third, the response to a given stimulus parameter changes over time, such that responses do not depend only on the current stimulus parameter value but also on the history of stimulation. That is, responses adapt. The first two principles indicate the existence of neural dictionaries-sets of quantitative, systematic rules for representing aspects of the outside world in terms of neural responses. The third principle implies that those rules change over time: the same stimulus parameter value can evoke different responses depending on its context. This is a key aspect of neural coding, repeatedly confirmed over the decades in many experimental situations.