State-of-the-art imaging techniques such as magnetic resonance imaging (MRI) allow changes within the brain to be visualised at a structural level. Gross morphological changes are likely to be permanent, and could be the result of insults of varying severity early in life during a critical developmental period. However, in the case of human congenital leptin deficiency, a mutation which results in morbid obesity, MRI investigation has demonstrated that leptin therapy in adult life not only induces a significant reduction in body weight but also changes brain tissue composition. Grey matter tissue was increased in a number of brain areas. Interestingly, analogous outcomes are observed in ob/ob mice, which also have a mutation in the leptin gene. Untreated ob/ob mice have smaller brains than their wild type littermates but show increased brain weight following leptin treatment. More subtle changes within the brain, such as those induced by nutritional challenges, may be short-term and reversible following an appropriate dietary intervention. In such cases, functional MRI (fMRI) may reveal differences in brain metabolism and activity following a visual, olfactory or taste stimulus, or during computerised trials.