Functional brain imaging and its application to uncover mechanisms driving food intake in humans

The control of food intake involves complex and powerful neural mechanisms whose functioning has critical repercussions for alimentary behaviours and the regulation of energy balance. Recent research also from cognitive neurosciences indicates that homeostatic (repletion-driven) and hedonic (reward-driven) systems in the brain concur in achieving an integrated regulation of human alimentary activity. Modern societal changes, related to unrestricted availability of energy-dense palatable foods at low costs and widespread presence of compelling alimentary cues, are considered to contribute to a food consumption driven mainly by hedonic properties rather than energy requirements, and result among the causes of worldwide obesity epidemics. Functional neuroimaging permits the exploration of the human brain systems involved under the different conditions of alimentary relevance, through the quantitative evaluation of regional blood flow, metabolic activation of defined cerebral networks or molecular bioavailability of brain receptors specifically traced. Such a framework of different imaging techniques appears uniquely suited to investigate the functional integration of the neural processes which underpin the interplay between homeostatic drive for feeding and the conscious experience of pleasure and reward concurring to the control of food intake. Therefore, these techniques provide an invaluable tool in gaining a detailed comprehension of physiology underlying alimentary behaviours and their derangements, and in detecting new strategies against obesity which interact also on brain mechanisms involved in the control of food intake and energy balance. In the present short review, basic principles of the most used functional neuroimaging techniques will be examined and the commonest acquisition protocols and processing methods will be briefly presented, along with a short overview of the brain systems involved in food intake regulation and a concise report of the main findings obtained with these techniques.