FIG. 1.

Cluster tree (top) and scree plot (bottom) for 87 parabrachial nucleus (PBN) neurons. The arrows (scree plot) indicate 2 major breakpoints in the clustering process, corresponding to the division of the population into 3 “superclusters” then further into clusters (also denoted by a dashed line extending to the cluster tree): the 6 clusters included bitter-best (B-best), acid/bitter (AB), acid/salt (AN), salt-best (N-best), umami/salt/sweet (UNS), and sweet/umami (SU). The taste qualities that elicited a significant response ≥25% of the maximum response are listed for each neuron; capital letters denote a response ≥50% of the maximum. With the exception of umami, a quality is listed if any stimulus of that quality elicited a response, but for umami, both monosodium glutamate (MSG) and monopotassium glutatmate (MPG) responses were required because most N-best cells responded to MSG but not MPG, implying that the sodium ion was the effective stimulus. A = sour [HCl or citric acid], B = bitter [quinine, cycloheximide, PROP, denatonium, or quinine], N = salty (NaCl or sodium gluconate), S = sweet (sucrose or glycine), U = umami (MSG and MPG).