In May of 2008, the ScienCentral Blog published a posting regarding studies from the journal Cell Metabolism which suggests a relationship between hunger and a hormone, ghrelin. The study uses MRIs to explore whether the presence of ghrelin makes food look more appetizing which in turn makes the person feel hungry.
The posting gives a complete explanation of the study and a short (1:19) YouTube video clip. The site includes links to clips on other websites for those not having access to YouTube. The blog entry can be found at http://www.sciencentral.com/video/2008/05/22/seeing-hungry/