The taste system is one of our fundamental senses, responsible for detecting and responding to sweet, bitter, umami, salty and sour stimuli. In the tongue, the five basic tastes are mediated by separate classes of taste receptor cells each finely tuned to a single taste quality. Here, we explored the logic of taste coding in the brain by examining how sweet, bitter, umami and saltiness are represented in the primary taste cortex. Using in vivo two-photon calcium-imaging we demonstrated striking topographic segregation in the functional architecture of the gustatory cortex. Each taste quality is represented in its own separate cortical field, revealing the existence of a gustotopic map in the brain. These results expose the basic logic for the central representation of taste.

Summary Perception of the thermal environment begins with the activation of peripheral thermosensory neurons innervating the body surface. To understand how temperature is represented in vivo, we used genetically-encoded calcium indicators to measure temperature-evoked responses in hundreds of neurons across the trigeminal ganglion. Our results show how warm, hot and cold stimuli are represented by distinct population responses, uncover unique functional classes of thermosensory neurons mediating warm and cold sensing, and reveal the molecular logic for peripheral warmth sensing. Next, we examined how the peripheral somatosensory system is functionally reorganized to produce altered perception of the thermal environment after injury. We identify fundamental transformations in sensory coding, including the silencing and recruitment of large ensembles of neurons, providing a cellular basis for perceptual changes in temperature sensing, including heat hypersensitivity, persistence of heat perception, cold hyperalgesia, and cold analgesia.

The ability of the taste system to identify a tastant (what does it taste like?) enables animals to recognize and discriminate between the different basic taste qualities1,2. The valence of a tastant (is it appetitive or aversive?) specifies its hedonic value, and the execution of selective behaviors. Here we examine how sweet and bitter are afforded valence versus identity. We show that sweet and bitter cortex project to topographically distinct areas of the amygdala, with strong segregation of neural projections conveying appetitive versus aversive taste signals. By manipulating selective taste inputs to the amygdala, we show that it is possible to impose positive or negative valence to a neutral water stimulus, and even to reverse the hedonic value of a sweet or bitter tastant. Remarkably, animals with silenced amygdala no longer exhibit behavior that reflects the valence associated with direct stimulation of taste cortex, or with delivery of sweet and bitter chemicals. Nonetheless, these animals can still identify and discriminate between tastants, just as wildtype controls do. These results help explain how the taste system generates stereotypic and predetermined attractive and aversive taste behaviors, and substantiate distinct neural substrates for the discrimination of taste identity and the assignment of valence.