Fig. 2

Taste pathways in the macaque and rat. In the macaque, gustatory information reaches the nucleus of the solitary tract (NTS), which projects directly to the taste thalamus (parvicellular division of the ventroposteromedial nucleus, VPMpc) which then projects to the taste cortex in the anterior insula (Insula). The insular taste cortex then projects to the orbitofrontal cortex (OFC) and amygdala (Amy). The OFC projects taste information to the anterior cingulate cortex (ACC). The OFC, ACC, and Amy project to the hypothalamus (HT). In macaques, feeding to normal self-induced satiety does not decrease the responses of taste neurons in the NTS or taste insula (and by inference not VPMpc). In the rat, in contrast, the NTS projects to a pontine taste area, the parabrachial nucleus (PBN). The PBN then has projections directly to a number of subcortical structures, including the HT and Amy, thus bypassing thalamo-cortical processing. The PBN in the rat then projects to the taste thalamus (VPMpc), which projects to the rat taste insula. The taste insula in the rat then projects to an agranular orbitofrontal cortex (AgOFC), which probably corresponds to the most posterior part of the primate OFC, which is agranular. (In primates, most of the OFC is granular cortex, and the rat may have no equivalent to this [210, 211] Fig. 2.1, see also 87 Fig. 1.1). In the rat, satiety signals such as gastric distension and satiety-related hormones decrease neuronal responses in the NTS (see text) and by inference therefore in the other brain areas with taste-related responses, as indicated in the figure. Adapted from ref. [89]