A model for regulation of appetitive state and behavioral choice by satiation via serotonin.

<p>A. The model builds on the relation that the default turn response to somatotopically mapped stimuli from the oral veil is avoidance, and that corollary outputs of the feeding network can change this response to orienting. The resting excitation state of the feeding motor network is set by endogenous 5-HT level, which is an inverse function of satiation state. Thus, network excitation state sums effects of satiation and appetitive sensory inputs (including effects of learned values of different prey odors). At increasing levels of feeding network excitation the turn response is switched from avoidance to approach. B. Increasing levels of 5-HT, through decline of satiation or by exogenous addition, increase feeding CPG excitation and thereby reduce the sensory thresholds for orienting and active feeding.