Now, using brain imaging and a simple experiment, researchers from Baylor College of Medicine in Houston have shown that a small midbrain region called the habenula activates when expectations are not met. In short, this tiny brain region helps you recognize when rewards fall short of what you expected to happen.
The report appears online in the journal Frontiers in Human Neuroscience.
"In healthy people, mistakes play a dominant role in the choices we make," said Dr. P. Read Montague, professor of neuroscience and director of the Computational Psychiatry Unit at BCM. "The brain computes signals that evaluate how close the obtained reward is to the expectation. When the reward is smaller than expected, the brain needs to learn to avoid actions that led to this outcome. In our study, we found that the habenula, a very small midbrain region responsible for learning, reproduction and stress response, could signal negative events."
Disappointment and withdrawal
The study began, in part, with earlier work by Dr. Ramiro Salas, instructor of neuroscience, and Dr. Mariella De Biasi, associate professor of neuroscience, both at BCM. Their previous work with mice showed that the habenula controls nicotine-withdrawal symptoms in addicted laboratory mice.
"In mice that have been treated with nicotine for two weeks, blocking nicotine receptors in the habenula only, but not in other parts of the brain, precipitates withdrawal symptoms," said Salas. "We believe that the habenula may be a critical target to develop improved anti-tobacco drugs. Since the habenula is important for signaling disappointment in the brain, we think that tobacco withdrawal is a form of continuing disappointment, which can only be tempered by another cigarette."
The first step in the current human study was to demonstrate that the habenula does respond to disappointment. The experiment used juice as a reward for an action given at different delayed times. Researchers were able to see how this affected the habenula by using fMRI images.
In order to analyze such an unusually small region of the brain, Dr. Philip Baldwin, instructor at the Human Neuroimaging Laboratory at BCM, developed novel fMRI (functional magnetic resonance imaging) computational processes. They used special computations based on prior knowledge of similar areas of the brain. The researchers hope to repeat this technique in order to study other small regions of the brain.
"These results expose the feasibility of human studies of habenula function under conditions modulated by the habenula, such as tobacco withdrawal, alcohol abuse, depression, or schizophrenia," The researchers wrote in their paper. "Ultimately we hope that our human studies, combined with genetic studies that are currently being initiated, will lead to targeted therapies based on any given individuals genetic makeup."
Funding for this research came from the Kane Family Foundation, the National Institute on Drug Abuse, the National Institute of Neurological Disorders and Stroke, and the Angel Williamson Imaging Center.