Psychobiology of feeding behaviour
Adequate nutrition is essential for survival and therefore is ensured by a complex brain system regulating the levels of various nutrients in the blood and in the body stores. This system includes two distinct mechanisms of control on food intake, i.e. the homeostatic and the hedonic control. Over the last two decades our knowledge of neural circuits and molecules involved in these mechanisms has improved substantially, in large part due to the findings of research in experimental animals and functional neuroimaging in humans. These findings also provide insight into the mechanisms underlying obesity and abnormal feeding behaviour in neuropsychiatric disorders. The hypothalamic network that regulates food intake and energy balance consists of interconnected neurons located in the arcuate (infundibular in humans) nucleus, ventromedial nucleus, paraventricular nucleus, dorsomedial nucleus, and lateral hypothalamic area. Central regulation is mediated by α- and β- melanocyte-stimulating hormone, neuropeptide Y, Agouti-related protein, γ-aminobutyric acid, brain-derived neurotrophic factor, and melanin-concentrating hormone. Peripheral signals that stimulate (orexigenic) or inhibit (anorexigenic) food intake are received by neurons in the medial zones of the hypothalamus, including signals from circulating nutrients (glucose, fatty acids), hormones (insulin, leptin, ghrelin), and gastrointestinal peptides (cholecystokinin and peptide YY3-36). The pleasure of palatable food is associated with activation of the brain reward system, including the ventral tegmental area, dopaminergic system, nucleus accumbens, ventral pallidum, and amygdala. Dopamine release in the nucleus accumbens mediates the motivational aspects of food intake, especially the drive to eat food that is hedonically desirable (“wanting”). Orexin, cocaine- and amphetamine- regulated transcript, and galanin play significant role in hedonic regulation of feeding. The hedonic reaction per se to the pleasure of food reward (“liking”) is regulated by endogenous opioids and endocannabinoids. There are homeostatic – hedonic control interactions via functional connections of nucleus accumbens with the prefrontal cortex, amygdala, and lateral hypothalamus, as well as between hypothalamic, cortical, and mesolimbic circuits. There is also a “top-down” control of human feeding behavior: interactions between cognitive and emotional processes could lead to different responses to food cues and changes in food intake.