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CHAPTER 3
The Pleasure-Pain Balance
euroscientific advances in the last fifty to one hundred years, including
advances in biochemistry, new imaging techniques, and the emergence
of computational biology, shed light on fundamental reward processes. By
better understanding the mechanisms that govern pain and pleasure, we can
gain new insight into why and how too much pleasure leads to pain.
Dopamine
The main functional cells of the brain are called neurons. They communicate
with each other at synapses via electrical signals and neurotransmitters.
Neurotransmitters are like baseballs. The pitcher is the presynaptic neuron.
The catcher is the postsynaptic neuron. The space between pitcher and
catcher is the synaptic cleft. Just as the ball is thrown between pitcher and
catcher, neurotransmitters bridge the distance between neurons: chemical
messengers regulating electrical signals in the brain. There are many
important neurotransmitters, but let’s focus on dopamine.
NEUROTRANSMITTER
Dopamine was first identified as a neurotransmitter in the human brain in
1957 by two scientists working independently: Arvid Carlsson and his team
in Lund, Sweden, and Kathleen Montagu, based outside of London. Carlsson
went on to win the Nobel Prize in Physiology or Medicine.
Dopamine is not the only neurotransmitter involved in reward processing,
but most neuroscientists agree it is among the most important. Dopamine may
play a bigger role in the motivation to get a reward than the pleasure of the
reward itself. Wanting more than liking. Genetically engineered mice unable
to make dopamine will not seek out food, and will starve to death even when
food is placed just inches from their mouth. Yet if food is put directly into
their mouth, they will chew and eat the food, and seem to enjoy it.
Debates about differences between motivation and pleasure
notwithstanding, dopamine is used to measure the addictive potential of any
behavior or drug. The more dopamine a drug releases in the brain’s reward
pathway (a brain circuit that links the ventral tegmental area, the nucleus
accumbens, and the prefrontal cortex), and the faster it releases dopamine,
the more addictive the drug.
DOPAMINE REWARD PATHWAYS IN THE BRAIN
This is not to say that high-dopamine substances literally contain
dopamine. Rather, they trigger the release of dopamine in our brain’s reward
pathway.
For a rat in a box, chocolate increases the basal output of dopamine in the
brain by 55 percent, sex by 100 percent, nicotine by 150 percent, and cocaine
by 225 percent. Amphetamine, the active ingredient in the street drugs
“speed,” “ice,” and “shabu” as well as in medications like Adderall that are
used to treat attention deficit disorder, increases the release of dopamine by
1,000 percent. By this accounting, one hit off a meth pipe is equal to ten
orgasms.
REWARDS AND DOPAMINE RELEASE
Pleasure and Pain Are Co-Located
In addition to the discovery of dopamine, neuroscientists have determined
that pleasure and pain are processed in overlapping brain regions and work
via an opponent-process mechanism. Another way to say this is that pleasure
and pain work like a balance.
Imagine our brains contain a balance—a scale with a fulcrum in the center.
When nothing is on the balance, it’s level with the ground. When we
experience pleasure, dopamine is released in our reward pathway and the
balance tips to the side of pleasure. The more our balance tips, and the faster
it tips, the more pleasure we feel.
But here’s the important thing about the balance: It wants to remain level,
that is, in equilibrium. It does not want to be tipped for very long to one side
or another. Hence, every time the balance tips toward pleasure, powerful
self-regulating mechanisms kick into action to bring it level again. These
self-regulating mechanisms do not require conscious thought or an act of
will. They just happen, like a reflex.
I tend to imagine this self-regulating system as little gremlins hopping on
the pain side of the balance to counteract the weight on the pleasure side. The
gremlins represent the work of homeostasis: the tendency of any living
system to maintain physiologic equilibrium.
Once the balance is level, it keeps going, tipping an equal and opposite
amount to the side of pain.
In the 1970s, social scientists Richard Solomon and John Corbit called this
reciprocal relationship between pleasure and pain the opponent-process
theory: “Any prolonged or repeated departures from hedonic or affective
neutrality . . . have a cost.” That cost is an “after-reaction” that is opposite in
value to the stimulus. Or as the old saying goes, What goes up must come
down.
As it turns out, many physiologic processes in the body are governed by
similar self-regulating systems. For example, Johann Wolfgang von Goethe,
Ewald Hering, and others have demonstrated how color perception is
governed by an opponent-process system. Looking closely at one color for a
sustained period spontaneously produces an image of its “opposing” color in
the viewer’s eye. Stare at a green image against a white background for a
period of time, and then look away at a blank white page, and you will see
how your brain creates a red afterimage. The perception of green gives way
in succession to the perception of red. When green is turned on, red can’t be,
and vice versa.
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