Gustatory neural coding in the pons

Third-order neurons from the pontine taste area (PTA) were analyzed in accordance with the across-fiber pattern theory of gustatory neural coding. Single neuron responses, evoked by chemical stimulation of the tongue, were recorded from the PTA of acute Nembutalized rats. They reveal that PTA neurons are broadly sensitive to stimuli representing the 4 putative basic taste qualities. Of 35 neurons, 33 responded to at least 3 of the 4 quality classes. Time course analyses indicate that stimuli which are shown to be alike in behavioral studies exhibit similar temporal response sequences. Correlations between all possible pairs of response patterns indicate that like-tasting chemicals elicit similar profiles of activity across the neural population. A multidimensional analysis indicates that three underlying physico-chemical dimensions (as yet undefined) bear upon the neural responses. In certain of their response properties, PTA neurons are like those of the (second-order) solitary nucleus; in other respects they auger the characteristics seen in the (fourth-order) thalamic neurons. It is concluded that the PTA is functionally as well as anatomically intermediate between the solitary nucleus and thalamus in the taste processing chain.