Findings By Glimcher and Platt Challenge Paradigm First Proposed 300 Years Ago by Descartes
How do the brains of humans and animals make decisions - what direction to move, what food to eat, where to sleep? Decision theory, a branch of the social sciences developed by economists and psychologists to explain behavior, has long proposed that humans and animals decide what to do in a given situation by first assessing the relative value of each possible option and then selecting the option which is of greatest value. In contrast, biological studies of the mind have relied upon Descartes' conception of the 'reflex', which, like the knee-jerk response to a physician's hammer, simply connects a single sensation and a single action. While this discrepancy between complex social scientific theories of behavior and simple biological reflexes has troubled neurobiologists for much of this century, until now no researchers have been able to identify specific neurobiological mechanisms for decision-making.
In the July 15th issue of Nature, NYU neuroscientists Michael L. Platt and Paul W. Glimcher have provided evidence of a true decision-making mechanism, of the type advocated by social scientists, within the brains of macaque monkeys. These findings raise the possibility that biological mechanisms which can account for the complex and often upredictable behavior of living animals have been identified. Platt and Glimcher have found neurons in the parietal cortex of monkeys that, although previously thought to transform visual signals into eye movements in a reflexive way, actually carry information about the amount of reward a monkey expects to receive for making the movement. They found that the activity of these neurons was, like the behavior of the monkey, not predictable simply from the appearance of the visual world, but reflected the value the monkey placed on the movement.