ABOVE: Distribution of the neurons responding to five gustatory stimuli (S: sucrose, N: NaCl, CA: citric acid, Q: quinine, W: water)


The paper
K. Chen et al., “Spatially distributed representation of taste quality in the gustatory insular cortex of behaving mice,” Curr Biol, 31:247–256.e4, 2020. 

Sensory information is often mapped onto the brain in a physical sense. The most famous case is that of the cortical homunculus, which depicts how representations of sensations of touch in the somatosensory cortex are spatially distributed according to where on the body touch was felt. Similar patterns of neurological organization can be found in the visual and auditory cortices, which map to locations in the visual field and in the cochlea, respectively. Smell does not follow any such organizational rules, however, and according to a new study of mice,...

While a 2011 study from the lab of Charles Zuker at Columbia University suggested that different taste sensations are clustered in the gustatory cortex of anesthetized mice, subsequent work has challenged this idea. Sure enough, when neuroscientist Alfredo Fontanini of Stony Brook University and his colleagues recently imaged the brains of awake mice tasting one of five different flavors, the team found no evidence of clustering. “The representation of taste is distributed,” says Fontanini. The five tastes tested, sugar, salt, citric acid, quinine, and water, were “equally distributed and sparse on the cortex. . . . There’s not really any specific position in the cortex where one is represented more strongly than others.”

Activated neurons (green) in the gustatory cortex of a mouse. (Thalamic fibers labeled in magenta.)

To coauthor Ke Chen, a former graduate student of Fontanini’s and now a postdoc at Harvard Medical School, this representation of taste makes sense, as there is no physical map on the body for the neural activity to correspond to—receptors for all tastes are distributed across the tongue. With both taste and smell, “there’s no map, basically,” says Chen—"the anatomy doesn’t allow that kind of [organization] to appear in [the] cortex.” 

Zuker, who has continued to publish evidence supporting the idea that taste representations are clustered, declined to comment on the new work. However, Jason Avery, a cognitive neuroscientist at National Institute of Mental Health’s Laboratory of Brain and Cognition who was also not involved in the study, says he hopes the research will help put to bed the uncertainty about the way tastes are mapped in the brain. 

The study from Fontanini’s group took previous work “one step further in awake, behaving animals, and showed you don’t see spatial clustering. . . . It all seems to be very broadly spatially distributed,” says Avery, who has found similar results in humans. This is “very, very strong evidence” for the distributed nature of taste representations in the gustatory cortex, he notes. 

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