INTERPRETATIONS CONCERNING NEURAL CODING DERIVED FROM EXPERIMENTS ON SMELL (AND TASTE)

Sensory coding taking place at the level of receptor cells, and the adjacent neuronal circuitry is a conditio sine qua non for processing of olfactory (and taste) stimuli. However, those sensory events do not represent the whole coding process. Different features concerning the stimuli in question are being “ascribed” to the corresponding neural message processed by the brain, probably. The added parts of the code are derived from two sources, apparently: from information concerning the proper stimulus (feature coding), and those generated from interactions between the stimulus and the brain (interaction coding). The results discussed in the present paper have been acquired (with a single exception) in psychophysical experiments. The aim was to draw inferences on the underlying coding processes. Candidates for feature codes could be considered (i.a.): the presence/absence of the stimulus, its quality, intensity, spatial localization (laterality), discriminability from other stimuli, mutual timing with respect to other stimuli, adherence to a stimulus sequence of increasing intensity. Interaction coding concerns (i.a.): the conscious nature of the stimulus, its hedonic interpretation, the signalling features added by Pavlovian (associative) conditioning, and its dependence of the actual state of the brain.