This is the 2007 version. Click here for the 2017 chapter 02 table of contents.

The Pleasure Centers

The discovery of "pleasure centers" in the brain is one of the more famous findings from brain stimulation research. It occurred by accident. James Olds, working with Peter Milner, inserted an electrode into a rat's brain, aiming for the reticular system. The electrode curved off its intended course and landed in a different area, probably near the hypothalamus.

A rat with an electrode in the "pleasure center" presses a bar to get brain stimulation

Olds put the rat in a box and stimulated its brain whenever the rat approached a certain corner. He expected the rat to stay out of that corner, but instead Olds observed the rat was "coming back for more," acting as though the brain stimulation was pleasurable (Olds & Milner, 1954).

How do humans react when electrically stimulated in the "pleasure centers"?

Further research showed that stimulation of areas in the limbic system produced pleasure in humans, too. Humans who receive electrical stimulation of the brain in the so-called pleasure areas usually reported mild sensations. Sometimes these resembled sensations leading up to sexual orgasm, sometimes they were harder to describe. Individuals in pain or depressed were most likely to find electrical stimulation of the brain very pleasurable. Others rated the stimulation as neutral or mildly pleasurable.

What chemical is associated with brain areas activated during pleasure?

In the decades since Olds and Milner reported the existence of pleasure centers, scientists have identified several regions that are activated by feelings of triumph, euphoria, sexual pleasure, and addictive behavior of all types, including non-drug addictions such as gambling. These brain pathways typically involve dopamine, an important brain chemical we will discuss later in the chapter. The fact that dopaminergic (dopamine-using) pathways seem to be activated by many different processes, all experienced as pleasurable, points to a hedonic (pleasure/pain) control system in mammalian animals, used to motivate a wide range of behaviors.

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