Decision Making

Dateline: 07/22/99

Decisions, decisions, decisions. How do humans and animals make decisions? New research suggests that decision theory, a branch of the social sciences, has been right all along. Humans make decisions based on the value of the outcome of the event.

For most of the century, biological explanations of this phenomena were based on the theories of Descartes - a type of reflex reaction theory. Similar to the jerking of the elbow or knee when hit by a doctor's hammer, a single reflex is associated with a single action. Social scientists, on the other hand, have promoted the idea that decisions are based on a complex set of circumstances. Humans and animals assess a particular situation and make a decision based on the outcome that will provide the most value for the individual.

In a recent set of experiments, researchers at New York University uncovered evidence for a biological decision making mechanism. In the study, the researchers found a set of neurons in the parietal cortex of macaque monkeys that carry outcome information. The expectation of what reward will be received based on a specific action is stored by these neurons.

In the first part of the experiment, the monkeys were shown two lights against a dark background. The animal could look at either light but received a fruit juice reward for looking at a certain light. Over time the researchers varied the amount of the reward received. By studying the activity of the parietal neurons, they found that the neurons "kept track" of the amount of reward received for a particular movement.

In the second part of the experiment, the monkeys were rewarded for looking at either light. However, the reward for one light was always more than the reward for the other. As expected the behavior of the monkeys was more unpredictable yet there was a high correlation between the frequency of choosing a certain target and the neuronal activity of the associated movement.

In addition, the neuronal activity levels were not predicted simply by what the monkeys saw. The "value" placed on a specific reward also came into play.

This research may have positive ramifications for parietal stroke victims. The inability of a patient to move a muscle for instance, may result from the inability to make a decision rather than the inability to perform the movement as was previously thought. Better understanding of what is happening could lead to treatment advances.

The Cartesian reflex has held an important place in the field of neurobiology. From the very descriptions and divisions of the nervous system to explanations of various behaviors, this motif has permeated the field. Unpredictable value-based decision making is not predicted in a reflex paradigm and increasing evidence about a biological basis for decision making may shatter the Cartesian concept.

Based on the research, the scientists believe that the often unpredictable behavior of humans and animals can one day be explained solely by biological mechanisms.

What do you think? Does this research seem plausible to you? If so, why? If not, why not? Come over to the Biology Forum and share your thoughts, opinions, and feelings.

For other information see:

• Neurobiology of Decision Making
  Press release from New York University.