GOOD FEELINGS / PLEASURE CENTERS [ NERVOUS SYSTEM ]

GOOD FEELINGS

Pleasure also has its centers In the brain. A Tulane University neurologist stumbled across one such center in the 1950s when he tried to electrically stimulate the brains of schizophrenics to break them out of their passivity. His patients told him their implanted electrodes created pleasant sensations. The neurologist, Robert G. Heath, seized upon the results, focused his attention on the brain’s pleasure centers, and published the 1964 book The Role of Pleasure in Behavior.

Together with the discovery of pain centers in the brain, research on the physical causes of the sense of pleasure seemed to prove the ancient wisdom that humans seek to act in ways that bring them pleasure and reduce or avoid pain. New paths of investigation have led to innovative treatments for addiction, which is a form of behavior based on compulsive forms of pleasure seeking. PET scans reveal how drugs such as cocaine and heroin activate the brain’s pleasure centers. Cocaine, for example, blocks a neuron’s reuptake mechanism, which causes dopamine to linger in the synaptic cleft.

PLEASURE CENTERS

Joy, happiness, pleasure-what-ever you want to call the positive feelings that bring rewarding sensations and make life worth living-arise from the sensations of security, warmth, and social well-being combined with an awareness of the rightness of such feelings. A healthy brain recognizes the conditions that give rise to pleasure and responds to them appropriately. An unhealthy brain, or one that has learned negative behaviors such as addiction, can miss out on experiencing life’s joys. Both are primarily a matter of chemistry.

The sensation of pleasure registers in several brain regions, including significant centers in the hypothalamus and nucleus accumbens , which lies below a portion of the basal ganglia linked to movement. All such pleasure centers rely on the chemical work performed by endorphins and neurotransmitters, particularly dopamine, to create and sustain a happy mood. Experiments with rats have demonstrated the key role of dopamine. In the 1950s, scientists wired rats’ brains so that when they pressed a bar, they received a mild electric shock to the hypothalamus. This stimulation registered as pleasure; the rats would rather press the bar than eat. However, in later experiments, rats wired for self-stimulation first received injections of drugs that block the receptors where dopamine normally binds, denying its pleasure-giving action. The rats no longer felt a pleasant reward from pressing a lever to stimulate their brain, and they stopped doing so. When humans take a similar dopamine-lowering medication, often in order to ward off hallucinations and other psychotic behavior, the drug’s success comes at a price. Delusions may leave, but so do joy and motivation. Conversely, drugs like amphetamines that increase the activity of dopamine in the brain lower the threshold for the perception of pleasure. Too much of a drug-induced pleasant sensation, however, can lead to addiction and manic moods.

When the skin warms, the sympathetic division of the autonomic nervous system dilates blood vessels near the surface and activates the sweat glands. When body temperature cools, the autonomic nervous system narrows surface vessels to send blood to deeper, more vital organs.

“The greatest pleasure of life is love,” said the Greek playwright Euripides nearly 2,500 years ago. Like other forms of pleasure, love is processed by brain chemistry, specifically by heightened levels of neurotransmitters in the pleasure centers. MRI scans of the brain relate the feeling of lust to estrogen and androgens; attraction-more emotional than physical-appears to be associated with serotonin and dopamine. The brain chemistry that supports long-term relationships such as lifelong commitment has been harder to pin down.

Playing key roles in the sensation of pleasure are oxytocin, endorphins, and phenylethylamine , or PEA, sometimes called the love drug. These chemicals help foster the “high” felt in the first stages of love, as well as the euphoria some-times reported by long-distance runners. Even a small pleasure, such as finding your lost car keys, begins with a tiny rise of these and similar neurotransmitters in the brain’s pleasure centers.