Pleasure and pain can be felt simultaneously. Think of a marathon runner, women in child birth, or the classic example of sadomasochistic sex. Although they may seem to be opposites, pleasure and pain, surprisingly, are similar biochemical events and engage the same brain circuit.
In his book The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning, and Gambling Feel So Good, David Linden tells of an experiment conducted at The University of Michigan in 2006 in which the researchers utilized brain scanning and a carefully controlled way of inducing muscle pain to show that the brain’s dopamine system is highly activated when someone experiences pain. The dopamine pathway has traditionally been best known for being the core of the pleasure/reward circuit. As a matter of fact, the greatest dopamine release was seen in the subjects who reported the greatest pain.
Now, what in the heck does that mean?
The interpretation is not really clear. First of all, we have to consider that even the most sophisticated brain scanning equipment in humans is crude when compared to the precise information that can be gathered from electrodes actually inserted into the brains of rats. When a similar experiment was conducted at the Imperial College London with rats, two different patterns of responses were recorded to painful stimulus – one in which dopamine neurons were inhibited by pain and one in which dopamine neurons were activated by pain.
This finding suggests that there are two parallel circuits. One is the well-known pleasure circuit activated by rewards, such as food or sex, and inhibited by pain. The second is a “salience circuit” that is activated by both pleasure and pain and closely tied to the emotional meaning given to the stimuli. Other experiments indicate that, in terms of brain activation, emotional pain overlaps the physical pain pathway. Linden writes:
In the lexicon of cognitive neuroscience, both pleasure and pain indicate salience, that is, experience that is potentially important and thereby deserving of attention. Emotion is the currency of salience, and both positive emotions like euphoria and love and negative emotions like fear, anger, and disgust signal events that we must not ignore.
This suggests that dopamine acts as an interface between physical and emotional events and that dopamine is released with both positive and negative stimuli. The determining mechanism here is the salience of the stimuli — the importance of it and the meaning given to it by the person experiencing it. This may be why meditation and other thought therapies are proving so effective in treating pain.