What is pleasure?
Pleasure can mean different things to each of us. For some it might be doing a sport, while for others it could be practicing yoga, eating ice cream, meditating, sailing a boat, love-making, having a religious experience, or simply lying on a beach. The ancient Greeks talked of happiness as being a combination of hedonia (pleasure) and eudaimonia (well-being and human flourishing by doing "good work" for others).
Certain pleasures have been studied neurologically, using a non-invasive brain scan called functional magnetic resonance imaging, or fMRI. An fMRI scan tracks changes in blood flow (hemoglobin) to various brain regions as a result of a specific stimulus. The more hemoglobin (therefore, the more oxygen) to a specific brain site, the more activity.
A significant body of scientific research has been published evaluating brain responses to four specific pleasurable stimuli: eating chocolate, listening to music that causes “frissons" (those thrilling “goosebumps” and “chills up or down the spine” that one gets to particularly pleasurable music), sexual climax, and, for those who unfortunately have a need for them, taking addictive drugs, i.e., drugs like cocaine and heroin, which stimulate the brain’s so-called mu-opioid and cannabinoid systems.
All four of these distinct, pleasure-inducing stimuli (chocolate, music, orgasm, addictive drugs) activate the same brain areas, anatomically adjacent to each other in a region called the medial forebrain (MFB). These areas are: 1) the ventral tegmental area (VTA) ( specifically a little blob of neurons in the VTA called the nucleus accumbens); 2) the prefrontal cortex; 3) the anterior cingulate cortex (especially its subgenual area, above the nucelus accumbens (not shown)); and 4) the amygdala.
These four brain areas are part of what cognitive neuroscientists describe as the Reward-Pleasure System. What we feel as desire and pleasure occurs in this system, which is also sometimes referred to as the Wanting/Liking System. This system tells the memory centers in the brain to pay attention to everything associated with that experience, so it can be repeated in the future. The Reward-Pleasure System is activated and controlled by molecular neurochemicals called neurotransmitters, specifically dopamine, serotonin, and oxytocin.
Evolutionarily, the Reward System is an ancient pathway: the use of dopamine neurons to interconnect behavioral responses to natural rewards has been observed in various species of worms and flies, whose ancestors were around two billion years ago!
These three neurotransmitters - dopamine, serotonin and oxytocin - mediate every pleasurable moment, including the “giving experience,” so much so that Eva Ritvo M.D., vice-chair of psychiatry at the University of Miami School of Medicine, has termed them the “Happiness Trifecta.”
Nerve-nerve cables, called neural networks, interconnect the pleasure centers. These neural networks work electrically, as well as chemically through the neurotransmitters. When we experience pleasure, we are, in essence, getting a reward.
Much of pleasure has to do with what cognitive neuroscientists call the "Wanting/Liking" system in the brain, which is part of the "Reward-Pleasure" circuit.
Hedonic Hotspots, Enkephalins and Anandamides
Things are actually a little more complicated than the Happiness Trifecta of dopmaine, serotonin and oxytocin. University of Michigan researchers Morton Kringelbach, Terry Robinson and Kent Berridge have discovered that there are neurochemical differences in our brains between “wanting” something and “liking” it.
The “Wanting” or "Desire" part of the system is largely mediated by dopamine, the same neurotransmitter that is involved in drug addiction with cocaine and heroin. Dopamine, according to Berridge, contributes more to motivation ("Wanting") than to the actual sensation of pleasure ("Liking") itself.
The “Liking" (or "Pleasure") system” in the brain is mediated by neurotransmitters called enkephalins and anandamides. There specific areas in the brain which have dense populations of these neurotransmitters. These areas serve as waystations for "Liking." Berridge calls these “Liking" system brain areas “hedonic hotspots.” ("hedonic” means "pleasant" (recall the ancient Greeks, hedonia, and our modern-day notions of hedonism).
The enkephalins bind mostly to what are known as opioid (mu-opioid) receptors in the brain. The anandamides, in contrast, bind to cannabinoid receptors. They are termed cannabinoid because they are similar to receptors which bind the cannabinoids (molecules which are also contained in marijuana). Yes, we humans make our own opioids and cannabinoids in our brains, in much smaller concentrations than if they are taken externally. Nonetheless, isn't it fascinating that opioids and cannabinoids are endogenously manufactured in our brains !?
A bite of chocolate, for example, prompts neurons in these hedonic hotspot areas to release neurotransmitters in the encephalin family, which are endogenous opioids that are made in our brains. According to Berridge, these enkephalins then interact with receptor proteins that cause the release of anandamide, our brain’s own home-made version of a marijuana cannabinoid. The anandamide, in turn, can interact with other neuronal receptors, producing more enkephalin and intensifying the pleasurable experience.
Interestingly, these anandamide (cannabinoid) receptors are located much more densely in the cerebral cortex ("the "thinking brain") than in the limbic system of the mid-brain (the "subconscious brain").
What does this mean? It means that when we desire, seek, or are motivated for pleasure, we release lots of dopamine to get what we want. When we get what we want ("sex, drugs, rock and roll," and chocolate), we really like it, through the release of enkephalins and anandamides.
What is the role of music in human evolution? Are humans hard-wired for music? Music may have a foundational and evolutionarily adaptive role in our brains.
That is the topic for the next A Musical Vision essay.
@ Vincent P. de Luise MD 2015