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The Brain Reinforces Its Preferences


  • Repeating a behavior reinforces it.
  • Cancelling a behavior makes the desire to do it go away.

Emotional Behavior Is Largely Learned

Conditioned learning: the learning depends on repeating conditions in which events are closely associated, in time and meaning. In Pavlov's original experiments: 1) Dog naturally likes food, salivates at the thought of eating (no learning required -- called "unconditioned" stimulus. 2) Sound from tuning fork is heard by dog, but has no meaning related to food. 3) When sound given immediately before food, when repeated many times, dog learns to associate the two. 4)  Upon hearing the sound, dog anticipates food, even though none is present. Both sound and the response are now conditioned.

Another Kind of Conditioning: Operant Conditioning

Another kind of learning is called "operant conditioning."  This is how animal trainers teach circus animals and show animals to do tricks. They "shape" a new behavior for an animal in a series of small steps, giving a reward when the animal accidentally performs the desired behavior. At each step, the animal learns an association between the behavior and the reward. 

You can perform this experiment on a "cyber bird." Click here. In this simulation, the bird occasionally pecks at a spot on the wall of its cage.  If you give him a food pellet each time he pecks, he will start pecking much more. If you stop rewarding, he will slow down or stop pecking. See also Activity #3 for an experiment on conditioning.

Positive Reinforcement

When a stimulus activates the "reward system" in the brain, repeating the stimulus can produce compulsive behavior to seek that stimulus. This can lead to additions,  such as drug addiction, compulsive gambling, or over-eating. In other words, the brain learns to become addicted.

The brain's "reward system" is driven partly by the neurotransmitter, dopamine and norepinephrine. If neurons in the reward system are getting bathed in these transmitters, you feel good. Note the structural similarity of these two transmitters.





People with Behavioral Disorders May Have Low Dopamine

Brain scans, averaged over 5 obese people and 5 people of normal weight, with the scan tuned to detected receptor molecules for dopamine. The bright areas are where the dopamine receptors are. The obese people had fewer dopamine receptors. That is, their reward system was not getting the normal amount of stimulation. Similar dopamine-receptor deficiencies have been seen in drug addicts. Source: National Institute of Drug Abuse.

The obvious interpretation is that obese people don't get enough "reward" from life, and that they over-eat to compensate. Another possibility is that their over-eating over-stimulates the dopamine system and causes the dopamine-receptor system to "down-regulate." That is, the brain quits making as many receptors because there is a super-abundance of dopamine. Receptor down-regulation from over-stimulation has been well documented in numerous other kinds of situations. Can you think how to test that possibility?

Drug addictions

Craving for any sort of drug (alcohol, tobacco, cocaine, etc.) seems to involve this same dopamine reward system found in obesity. Normal rewarding things, like eating ice cream or a good steak, trigger the release of dopamine in the reward system. This dopamine is soon destroyed or taken back up. But taking addictive drugs tend to promote sustained high levels of dopamine - a chemical  "flood." 

This creates a problem. The neurons that make dopamine shut down for a while ("down regulate" as we mentioned above). To get the same happy, feel-good experience, ordinary rewards, like ice cream or steak, no longer make us happy. The addict has to take the drug to experience that same intense feeling of reward. The addict is also driven by the desire to avoid the suffering experience the he feels without the drug.

Practical Preventive Measures

  1. Don't do things that can cause you harm, even if they "feel good" at the time.
  2. Don't repeat behaviors that are bad for you.
  3. Substitute "good" reinforcers for "bad" ones.

  Brain Controls Movement

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