How The Brain Makes Decision

Scientists reported that they may have come close to understanding a biochemical process in the brain that influences the ability to make the right decisions -- to predict what behavioral choices may be most useful for survival or in helping themselves. It seems that this may explain why upwards of 50% of people with schizophrenia have no insight into their illness and therefore can't make the decision to help themselves by taking medication. The experiments on monkeys reported in the journal Science indicate that brain cells which secrete the neurotransmitter dopamine play a key role in this process, signaling the best course of action for a given situation. The new explanation for how people come to read sensory clues around them and choose from a number of behaviors for maximum benefit are based on more than 15 years of primate experiments in Switzerland, said Dr. P. Read Montague, professor of neuroscience at Baylor College of Medicine in Houston, Texas. In these experiments by Montague's co-author Dr. Wolfram Schultz of the University of Fribourg, electrodes were attached to the brains of monkeys to record electrical activity in dopamine-secreting brain cells (neurons). The monkeys were trained to press a level in response to a certain pattern of light to receive a reward (a squirt of juice). "And the electrical activity in these neurons is known to reflect the delivery of this chemical, dopamine, to the frontal cortex. Dopamine is one of several neurotransmitters thought to regulate emotional response, and is suspected of playing a central role in schizophrenia, Parkinson's disease, and drug abuse," Montague says. "We think these dopamine neurons are making guesses at likely future rewards. The neuron is constantly making a guess at the time and magnitude of the reward." "If what it expects doesn't arrive, it doesn't change its firing. If it expects a certain amount of reward at a particular time and the reward is actually higher, it's surprised by that and increases its delivery of dopamine," he explains. "And if it expects a certain level (of reward) and it actually gets less, it decreases its level of dopamine delivery." Thus, says Montague, "what we see is that the dopamine neurons change the way they make electrical impulses in exactly the same way the animal changes his behavior. The way the neurons change their predictions correlates with the behavioral changes of the monkey almost exactly." Montague and MIT co-author Dr. Peter Dayan pulled together Schultz's findings and created a mathematical theory based on the idea of those neuronal guesses and then compared it to what was actually recorded in primates. "It dead-on predicts the way those cells are going to fire," Montague says. The researcher notes further evidence supporting the theory comes from recent brain-scan studies of people who are missing parts of their frontal cortex. "They're missing the part of their frontal cortex that provides input to these dopamine neurons in their midbrain," says Montague. "And interestingly enough, these people lack the ability to make correct decisions about the future when you give them psychological tasks asking them that -- which is exactly what you'd predict from the way we construe these neurons." Montague says the findings in primates may also increase our understanding of the brain mechanisms affected by drug abuse. "This is an important piece of the puzzle because we know dopamine is involved in the same systems that are usurped by drugs of abuse, like cocaine."