This is the 2007 version. Click here for the 2017 chapter 09 table of contents.

Pleasure Centers in the Brain

You may recall from Chapter 2 that so-called "pleasure centers in the brain" were discovered accidentally by James Olds. He implanted an electrode in a rat's septum, part of the limbic system. He was preparing to do avoidance conditioning with the rat, but instead he observed the rat "coming back for more," lingering in the area of the cage where it received the brain stimulation. Olds realized he had stumbled on an area of the brain that produced pleasure.

How did Olds discover "pleasure centers" in the brain?

Olds set up an apparatus in which the rat could self-administer rewarding stimulation. Each time it hit the bar that stuck out from the side of the chamber, an electrical stimulus would be delivered to the pleasure centers.

Olds and colleagues showed that a rat would press a bar up to 3000 times an hour for rewarding brain stimulation. In another experiment, a rat pressed a bar every two seconds for 20 days, a total of 850,000 self-stimulations. If the intensity of pleasure is measured by the amount of work animals will perform to get a stimulus, then stimulation of the pleasure centers must be pleasurable indeed in a rat.

However, as noted in the Chapter 2 discussion, stimulation of the pleasure centers in humans is not so powerful. It feels great to people who are depressed or in pain, but it is "nothing special" to people who are already in a good mood. Cocaine acts the same way, which suggests both cocaine and stimulation of the pleasure centers may involve the same mechanism: release of dopamine in the midbrain.

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