The Representation of Information About Taste and Odor in the Orbitofrontal Cortex

Complementary neurophysiological recordings in macaques and functional neuroimaging in humans show that the primary taste cortex in the rostral insula and adjoining frontal operculum provides separate and combined representations of the taste, temperature, and texture (including viscosity and fat texture) of food in the mouth independently of hunger and thus of reward value and pleasantness. One synapse on, in the orbitofrontal cortex, these sensory inputs are for some neurons combined by learning with olfactory and visual inputs, and these neurons encode food reward in that they only respond to food when hungry and in that activations here correlate with subjective pleasantness and with individual differences in and cognitive modulation of the hedonic value of food. Information theory analysis shows a robust representation of taste in the orbitofrontal cortex, with an average mutual information of 0.45 bits for each neuron about which of six tastants (glucose, NaCl, HCl, quinine-HCl, monosodium glutamate, and water) was present, averaged across 135 gustatory neurons. The information increased with the number of neurons in the ensemble, but less than linearly, reflecting some redundancy. There was less information per neuron about which of six odors was present from orbitofrontal olfactory neurons, but the code was robust in that the information increased linearly with the number of neurons, reflecting independent information encoded by different neurons. Although some neurons were sharply tuned to individual tastants, the average encoding was quite distributed.