• Ghrelin
• brain imaging
• peptide hormones
• satiety
• obesity and anorexia
• gastro-oesophageal reflux disease
• gastrointestinal physiology
• nerve—gut interactions
• brain/gut interaction
• gastrointestinal motility

Since the US army surgeon, William Beaumont, first described the effects of emotion on the gastric function of Alexis St Martin, a Canadian voyager who developed a gastrocutaneous fistula after a gunshot wound,1 considerable progress has been made in our understanding of the human brain–gut axis. Animal studies show that this axis, which comprises neural, hormonal and immune pathways, modulates all aspects of gut function and, perhaps most importantly, also modulates feeding behaviour. Our understanding of the human brain–gut axis has been greatly facilitated by functional brain imaging techniques, which have been used extensively to study visceral pain in health and disease. This work has led to important insights into the visceral pain neuromatrix, and its modulation by psychological and pharmacological factors.2 With advanced brain imaging methods, it has now become possible to study brain–gut communication that occurs through gut peptide hormones, affording an opportunity to understand the central mechanisms of satiety in health and conditions such as obesity and anorexia.

Eating behaviour is not just dictated by metabolic requirements but also by hedonic, psychological, social and environmental influences. Indeed, extremes of eating behaviours leading to obesity and anorexia in the Western world have occurred in the setting of abundance but also a more demanding and stressful environment. While animal studies have improved our basic understanding of the homoeostatic mechanisms of energy balance, translation to humans is limited by the inability to investigate the influence of hedonic and psychological influences on eating behaviour. This limitation is now being overcome through exciting recent brain imaging studies in humans, which are demonstrating a network of brain areas that are activated in response to nutrient ingestion, food cues and orexigenic and anorexigenic gut peptides. …