The Representation of Taste Quality in the Mammalian Nervous System

Abstract

The process by which the mammalian nervous system represents the features of a sapid stimulus that lead to a perception of taste quality has long been controversial. The labeled-line (sparse coding) view differs from the across-neuron pattern (ensemble) counterpoint in proposing that activity in a given class of neurons is necessary and sufficient to generate a specific taste perception. This article critically reviews molecular, electro-physiological, and behavioral findings that bear on the issue. In the peripheral gustatory system, the authors conclude that most qualities appear to be signaled by labeled lines; however, elements of both types of coding characterize signaling of sodium salts. Given the heterogeneity of neuronal tuning functions in the brain, the central coding mechanism is less clear. Both sparse coding and neuronal ensemble models remain viable possibilities. Furthermore, temporal patterns of discharge could contribute additional information. Ultimately, until specific classes of neurons can be selectively manipulated and perceptual consequences assessed, it will be difficult to go beyond mere correlation and conclusively discern the validity of these coding models.

Breadth of Tuning and Taste Coding in Mammalian Taste Buds

“…This communication comprises the first level of information processing in the gustatory system. These results support the notion that the taste bud likely serves a more complex role than simply transmitting signals from molecular receptor to afferent nerve (Spector and Travers, 2005;Roper, 2006). Huang et al, 2007).…”

“…Vallate taste buds are innervated by the glossopharyngeal nerve (GL). Previous studies have examined responses of individual afferent fibers in the GL and classified the fibers according to their responses to taste stimulation (for review, see Spector and Travers, 2005). Although there are species-specific differences, several classes of afferents are typically encountered in the GL: N fibers (salt-best), S fibers (sweet-best), Q fibers (quinine/bitterbest), and H fibers/A fibers (broadly tuned acid-and electrolytesensitive fibers).…”

Caffeine induces gastric acid secretion via bitter taste signaling in gastric parietal cells

“…Based on our results, we hypothesize that bitter perception of caffeine in the mouth generates a signal of aversion, which leads, via vagal withdrawal, to inhibition of GAS (41). However, when bitter compounds reach the stomach, increased GAS could aid degradation or removal of the potential toxins.…”

Behavioral Discrimination between Sucrose and Other Natural Sweeteners in Mice: Implications for the Neural Coding of T1R Ligands

“…The putative bitter taste evoked by L-serine could provide a plausible explanation for the apparent difference in the affective potency of L-serine and sucrose (Dotson and Spector, 2004). Another possibility is that, compared with sucrose, the L-amino acids may have a different temporal profile of interacting with their receptors that may lead to distinguishable differences in the rise and decay of the sensation (for more discussion, see Spector and Travers, 2005). Last, it should be pointed out that some of the concentrations of the amino acids tested, although within the range of those commonly used to assess the behavioral responsiveness of rodents in other experiments (Pritchard and Scott, 1982;Iwasaki et al, 1985;Zhang et al, 2003;Zhao et al, 2003), were relatively high.…”