Friday, September 16, 2016

PLEASURE AND REWARD: WANTING, LIKING, AND HEDONIC HOTSPOTS

Vincent P. de Luise MD


What is pleasure?   

Pleasure can mean different things to each of us. Eating ice cream, love-making, meditating, sailing, having a religious experience, or simply lying on a beach, can all engender feelings of pleasure. The ancient Greeks talked of happiness as being a combination of two concepts: hedonia (pleasure) and eudaimonia ("well-being" or "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 dark 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. 

Axial section of brain. From Hartley.com

These four brain areas are part of what cognitive neuroscientists term the Reward/Pleasure system. What we feel as desire and pleasure occurs in this system, also referred to as the Wanting/Liking system.

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 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 at the molecular level by chemicals, called neurotransmitters, specifically dopamine, serotonin and oxytocin. Evolutionarily, the Reward/Pleasure system is ancient; dopamine neurons that interconnect behavioral responses to natural rewards have been observed in various species of worms and flies, whose ancestors were around five hundred million years ago.

Pleasure, Reward and the "Happiness Trifecta"

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.” Dr. Ritvo asserts that "giving is a powerful pathway for creating more personal joy and improving health. Any activity that increased the production of these neurotransmitters will cause a boost in mood and cause happiness." Dopamine is connected to motivation, reward and arousal. Serotonin is connected  to memory, learning, sleep and appetite. Oxytocin, nicknamed "the cuddle hormone," has a powerful effect on the brain and the body. "When oxytocin begins to flow, blood pressure decreases, bonding increases, social fears are reduced, and trust and empathy are enhanced” Dr. Ritvo explains. 

Giving to others triggers a release of oxytocin, which boosts mood and counteracts the stress hormone, cortisol. The higher the level of oxytocin, the more one wants to help 
others, Interestingly, when oxytocin is boosted, so are dopamine and serotonin. According to Dr. Ritvo, "even small repeated boosts of the Happiness Trifecta will produce a benefit. Donating money or time... are wonderful waus to give. When we step outside of ourselves long enough to help someone else, something wonderful is waiting for us in return: the Happiness Trifecta neurochemicals are all boosted." 

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.  Pleasure has a lot 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, Anandamides 

However, 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 are specific area in the brain which have dense populations of these neurotransmitters. These areas serve as waystations for "Liking." Berridge calls these loci "hedonic hotspots" ("hedonic" means "pleasant (recall the ancient Greek concept of hedonia and our present-day notions of hedonism).

The enkephalins bind mostly to what are known as opioid (mu-opiod) receptors. The anandamides, in contrast, bind to cannabinoid rceptors. They are termed "cannabinoid" receptors because they are similar to the cannabinoid receptors (molecules which are contained in marijuana). Yes, interestingly, we humans make our own endogenous opiods and cannabinoids (inwe  much smaller concentrations than if they are taken externally). The anadamide (cannabinoid) receptors are more densely located in the cerebral cortex ("thinking brain") than in the mid-brain limbic system ("subconscious brain").

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.

Two key hedonic hotspots are a specific region in the nucleus accumbens called the medial shell, and another area nearby, the ventral pallidum (different from the ventral tegmentum discussed earlier). What does this mean? It means that when we desire or seek pleasure, we release dopamine to get what we want. When we finally get it (sec, drugs, rock and roll, choclate), we really like it, through the release of enkephalins and anandamides.It turns out that, among these stimuli, it is music that is particularly exciting to humans, especially music that causes those "chills" down one's spine, the musical frissons. Music is a powerful stimulus of the brain's pleasure center, activating the same neural network receptors as do addictive drugs, sexual climax and dark chocolate. Why would that be? 

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 a future A Musical Vision essay.

@ 2015,2017 Vincent P. de Luise MD 


Ritvo, E. Psychology Today April 20, 2014.
https://www.psychologytoday.com/blog/vitality/201404/the-neuroscience-giving


Kringelbach, M., and Berridge, K., The Joyful Mind, Scientific American, August 2012





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