ABSTRACT
Stimulus intensity is encoded by the mean frequency with which a sensory neuron fires. This is called frequency modulated (FM) coding. The relationship between stimulus intensity and response for static cells may be a simple linear one, as for example in skin thermoreceptor afferents. Often, however, the relationship is more complicated. Many skin mechanoreceptors and photoreceptors fall into this category. This type of relationship allows a very wide range of stimulus intensities to be encoded by quite small differences in firing frequency. It has the disadvantage, however, that for high intensities the ability to discriminate between differences in intensity is compromised. With frequency modulation coding, obtaining accurate information about stimulus intensity requires that enough time elapses for a neuron to fire several action potentials. Hence, FM coding is not well suited to conveying information about the precise timing of events.
