Cortical population coding of consumption decisions

The moment that a tasty substance enters an animal’s mouth, the clock starts ticking. Taste information transduced on the tongue signals whether a potential food will nourish or poison, and the animal must therefore use this information quickly if it is to decide whether the food should be swallowed or expelled. The system tasked with computing this important decision is rife with cross-talk and feedback—circuitry that all but ensures dynamics and between-neuron coupling in neural responses to tastes. In fact, cortical taste responses, rather than simply reporting individual taste identities, do contain characterizable dynamics: taste-driven firing first reflects the substance’s presence on the tongue, and then broadly codes taste quality, and then shifts again to correlate with the taste’s current palatability—the basis of consumption decisions—all across the 1-1.5 seconds after taste administration. Ensemble analyses reveal the onset of palatability-related firing to be a sudden, nonlinear transition happening in many neurons simultaneously, such that it can be reliably detected in single trials. This transition faithfully predicts both the nature and timing of consumption behaviours, despite the huge trial-to-trial variability in both; furthermore, perturbations of this transition interfere with production of the behaviours. These results demonstrate the specific importance of ensemble dynamics in the generation of behaviour, and reveal the taste system to be akin to a range of other integrated sensorimotor systems.