Mechanisms involved in the control of feeding behavior in relation to food flavor
Résumé
Introduction
Intake is one of the most essential behaviors, since human beings, like any living organism, require adequate nutrients for their survival. Ingestive behavior is controlled to maintain energy balance by peripheral and central mechanisms. When physiological needs are not being met, they will lead to motivation. Thus, being hungry will motivate us to find food, and the motivation will cease when needs are met. Ingestive behavior is thus initially due to a need related to internal signals (Fig. 10.1), in this case, hunger (physiological need) and appetite (urge to eat a food from which we expect pleasure and satisfaction). Sensory (visual, olfactory and, to a lesser extent, auditory) processing begins when a motivated animal searches for and detects a desired food. Once this food is found or prepared, the decision to start and maintain consumption involves active oral exploration. The sensory perception resulting from taste, odor, texture, and temperature of the food, that is, its flavor, allow us to analyze, identify, and eventually recognize the food, and will then be a central contributor in the decision to ingest or reject the food (Booth and Thibault, 2000; Small and Prescott, 2005). Flavors-related functions, that is, external signals, are a key prerequisite that allow us to judge the quality of the food. The multisensory properties of intraoral and ingested stimuli are conveyed to the brain through specialized taste, somatosensory, olfactory, and visceral sensory neurons that converge on several central nervous system (CNS) centers. Thus, once beyond the periphery, single neurons responding to gustatory stimuli are often found to be broadly tuned to diverse combinations of chemosensory, somatosensory, olfactory, and even visual information (Rolls and Baylis, 1994; Rolls, 2015). Furthermore, the CNS detects humoral signals that cross the blood–brain barrier, and transmit information not only about the properties of ingested stimuli, but also about physiological states, such as satiety (Zheng and Berthoud, 2008), thus providing additional modulatory influences for central gustatory neurons (Nakano et al., 1986). Neurons with these multimodal response properties, distributed through several CNS areas, integrate sensory and homeostatic information, participating together with neural circuits of affective, cognitive, and motor processing to organize ingestive behavior (Booth and Thibault, 2000; Kelley et al., 2005; Olivera-Maia et al., 2011). The treatment of the sensory information (perception) is a complex multimodal process. Food seeking and ingestion are also influenced by (1) memories of the orosensory, olfactory, and postingestive effects of previous encounters with a similar substance (Sclafani, 2004); and (2) emotional, cognitive, and social factors such as culture and context (Wilson, 2002; Olivera-Maia et al., 2011; Smeets et al., 2012). In summary, ingestive behavior is a complex phenomenon under the influence of three main mechanisms: homeostatic, hedonic, and cognitive (Fig. 10.1). The aim of this chapter is to describe some of these mechanisms, as well as their time course through the alimentary sequences.