Single and population coding of taste in the gustatory cortex of awake mice
Electrophysiological analysis has reveals much about the broad coding and neural ensemble dynamics that characterize gustatory cortical (GC) taste processing in awake rats, and about how these dynamics relate to behavior. With regard to mice, meanwhile, data concerning cortical taste coding have largely been restricted to imaging--a technique that reveals average levels of neural responsiveness, but that (currently) lacks the temporal sensitivity necessary for evaluation of fast response dynamics; furthermore, the few extant studies have thus far failed to provide consensus on basic features of coding. We have recorded the spiking activity of ensembles of GC neurons while presenting representatives of the basic taste modalities (sweet, salty, sour and bitter) to awake mice. Our first central result is the identification of similarities between rat and mouse taste processing: most mouse GC neurons (~66%) responded distinctly to multiple (3-4) tastes; temporal coding analyses further reveal, for the first time, that single mouse GC neurons sequentially code taste identity and palatability--the latter responses emerging ~0.5s after the former--with whole GC ensembles transitioning suddenly and coherently from coding taste identity to coding taste palatability. The second finding is that spatial location plays very little role in any aspect of taste responses--neither between- (anterior-posterior) nor within-mouse (dorsal-ventral) mapping revealed anatomical regions with narrow or temporally simple taste responses. These data confirm recent results showing that mouse cortical taste responses are not \"gustatopic,\" but also go beyond these imaging results to show that mice process tastes through time.