The brain has pathways of nerve fibers that run between cell groups, to carry information in a code, since the signal itself is simply the firing pattern of individual nerve fibers. Two major kinds of coding have been proposed. One proposes that each fiber from a sensory organ carries a certain kind of information alone, so that for example a class of fibers from the tongue are active only when there is a sweet substance but not when there is a sour one; this coding is called a "labelled line." The other proposes that the brain takes in the varied pattern of activity from a whole group of fibers, where each one has a somewhat different response to a whole range of stimuli, and determines from the overall pattern that one taste, for example, is "more sweet" while another is "more sour"; this coding is called the "across-unit pattern." This proposal uses a novel exploratory approach of artificial stimulation in the taste pathway to try to mimic the sensory activity. Stimulation to mimic the neural responses to sugar taste will be paired to licking of plain water by the animal, and the animal will be conditioned to avoid that experience. If the behavioral taste aversion is transferred to cause avoidance of naturally licking other sweet substances, then this technique will be validated as an important way to study what features of spatially and temporally distributed patterns of input are important for the brain to act on in producing relevant behavior. Results will be important to virtually all sensory systems, and to bioengineering/computational models as well, because of the active interest in how labelled lines or parallel processing work in distributed systems.
