People come to prefer particular foods by learning to associate that food with a predictive representation, and the scientists found that those predictive associations could be with something as arbitrary as a name brand.
John O'Doherty from the University of London and his colleagues also managed to trace where in the reward-processing regions of the brain such associations are developed, offering insights into the process of food preference.
The scientists described their findings in an article in the 5 January 2006 issue of Neuron.
In their experiments with human volunteers, the group first determined the subjects' rank-order preference of four juices - blackcurrant, melon, grapefruit, and carrot - and a tasteless, odourless control solution.
They then scanned the subjects' brains using functional magnetic resonance imaging (fMRI) as they established a Pavlovian conditioning association in the subjects. Such conditioning is the same type that Pavlov used to condition dogs to associate an otherwise irrelevant stimulus such as a bell with food.
In analysing the brain scans, the researchers detected significant responses reflecting learning of behavioural preferences in a region called the ventral midbrain, as well as an area of the ventral striatum. In the former region, the researchers found that the response increased with increasing preference for the juice.
And in the latter area, the researchers found a "bivalent" response, with the highest responses for the most and least preferred juices.
"It has long been known that associating brand items with other rewarding or appetitive stimuli, through the process of classical conditioning, makes it possible to modulate subjects' preferences," wrote the researchers. "This process may account in large part for the efficacy and power of advertising.
"The principal implication of the present study is that it provides an account of how predictive representations, learned through classical conditioning, come to elicit activity in the human brain that relate directly to subsequent behavioural preference. We suggest that such representations play an important role in the guidance of action based upon future reward, a form of elementary behavioural decision making."
The research was supported by a programme grant from the Wellcome Trust.