Many human behaviors—perhaps more than we would like to think—are, in essence, reflexes programmed into our brains when we are rewarded or punished for taking a particular action. New research is showing how the basal ganglia, deep inside the brain below the cortex, are important in learning from feedback, in the formation of good and bad habits, and even in brain disorders as diverse as Parkinson’s disease, ADHD, and addiction. Reflexes deserve respect, writes the author, and understanding how people differ in learning from positive or negative feedback may have implications for education as well as for treating diseases in which the basal ganglia’s systems go awry.
Before you read any further, grab a glass of your favorite beverage and set it down (no drinking yet). Done? Now, reach both hands around your back and touch your pinkies together. Then quickly take a sip of your drink. Go on.
Did you do it? If so, the next time you find yourself in a similar environment you will have a greater chance of spontaneously repeating this round-the-back pinkie act. Although that possibility may sound strange, your brain is actually programmed to reinforce actions that are immediately followed by rewards. This is especially true when the reward is unexpected (you probably did not expect to have a treat when you began to read this article).
Although most of us feel like we are in control of our actions, many of those actions can also be explained by principles of learning that are embedded in our neural machinery. Of course, this machinery is inordinately intricate and complex, The more a behavior is ingrained, the more its neural representations in the basal ganglia are strengthened and honed. involving several interacting systems, each with millions of neurons, billions of connections, and multiple neurotransmitters, all evolving dynamically as a function of genes, time, past experience, and current environment. But neuroscience is shedding light on how circuits linking two parts of the brain, the basal ganglia and the frontal cortex, contribute to learning both productive and counterproductive behaviors, and even to some neurological disorders. Those circuits can, for example, help account for genetically driven individual differences in whether we learn best from positive or negative reinforcement, and understanding them provides insights into decision making in people with Parkinson’s disease, attention-deficit hyperactivity disorder, and addictions.
Basal Ganglia Basics
The basal ganglia are a collection of interconnected areas deep below the cerebral cortex. They receive information from the frontal cortex about behavior that is being planned for a particular situation. In turn, the basal ganglia affect activity in the frontal cortex through a series of neural projections that ultimately go back up to the same cortical areas from which they received the initial input. This circuit enables the basal ganglia to transform and amplify the pattern of neural firing in the frontal cortex that is associated with adaptive, or appropriate, behaviors, while suppressing those that are less adaptive. The neurotransmitter dopamine plays a critical role in the basal ganglia in determining, as a result of experience, which plans are adaptive and which are not.
Evidence from several lines of research supports this understanding of the role of basal ganglia and dopamine as major players in learning and selecting adaptive behaviors. In rats, the more a behavior is ingrained, the more its neural representations in the basal ganglia are strengthened and honed.1 Rats depleted of basal ganglia dopamine show profound deficits in acquiring new behaviors that lead to a reward. Experiments pioneered by Wolfram Schultz, M.D., Ph.D., at the University of Cambridge have shown that dopamine neurons fire in bursts when a monkey receives an unexpected juice reward.2 Conversely, when an expected reward is not delivered, these dopamine cells actually cease firing altogether, that is, their firing rates “dip” below what is normal. These dopamine bursts and dips are thought to drive changes in the strength of synaptic connections—the neural mechanism for learning—in the basal ganglia so that actions are reinforced (in the case of dopamine bursts) or punished (in the case of dopamine dips).