Feeding behavior is a complex phenomenon involving homeostatic signals, and non-homeostatic inputs such as visual cues. In primates, exposure to food-related sensory cues has been shown to elicit cephalic phase responses as well as trigger central appetitive processing, in a motivationally-dependent manner. Neural structures consistently implicated in such responses and/or in the regulation of ingestive behavior in general, in both monkeys and in humans, include the amygdala, insula, striatum, hypothalamus, and frontal and occipital cortices. In humans however, the cerebral response to visual food stimulation remains minimally explored. / Functional Magnetic Resonance Imaging (fMRI) provides information about state-dependent changes in local neuronal activity in vivo. Using fMRI, the present dissertation examined changes in human brain activity to food and nonfood pictures following the pharmacological induction of hunger with the orexigenic hormone ghrelin (Study 1), and following manipulation of the cognitive state of food expectation (Study 2). / Our data reinforce the involvement of a distributed frontal-limbic-paralimbic circuit in the central processing of food imagery, under both experimental conditions. The first study revealed that intravenous ghrelin administration potently modulated food-associated neural responses III areas involved in reward, motivation, memory, and attention (amygdala, insula, orbitofrontal cortex, striatum, hippocampus, midbrain, visual areas). This suggests that metabolic signals such as ghrelin may promote food consumption by enhancing the appetitive response to food cues via engagement of the hedonic network. / The second study revealed that brain regions activated in the 'expectant' state (i.e. when subjects were anticipating food reward) were at least partially dissociable from those in the 'not expectant' state. In particular, recruitment of the dorsolateral prefrontal cortex, a principal component in the cognitive control network, exclusively in the 'not expectant' condition, may signal an attempt to suppress appetite in the absence of food expectation. Areas of convergence were observed in the amygdala and insula. / Obesity is rapidly becoming the major cause of excess mortality worldwide; therefore, understanding how the central nervous system controls appetite and nutrient consumption is of considerable interest. The projects in this thesis offer significant insights regarding the effects two select factors (one intrinsic and the other extrinsic) on the neural reaction to visual food stimuli, in healthy male participants.

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