I think we can all agree that a basic goal in life is the attainment of happiness, that mind state characterized by positive and pleasant thoughts and emotions. But how do we become happy? By definition, happiness requires some type of pleasure to be present. We need good feelings and good physical sensations. Furthermore, the pleasure must come first, before the happiness. Something, and I don’t care what it is, has to make you feel good before you can truly call yourself happy. As such, our behaviors and our motivations are shaped by that pleasure-seeking tendency. And that pleasure-seeking is mediated through the reward system, which has several different but interrelated components: liking, which describes the sensation of pleasure; wanting, which describes the desire to obtain the thing; and learning, the Pavlovian-esque conditioning. Basically, if we do something or expose ourselves to something (a fun social situation, a healthy food, the sun) that confers a survival and/or health benefit (improved social standing, some vital nutrient that our body needs, vitamin D production), our reward center “activates.” We like it, we want it, and we learn that having it is in our best interest.
Today, I’m interested in the “liking” part of reward – both the subjective experience of pleasure (“that hand massage feels good”) and the objective hedonic response (the neurochemistry that controls the hand massage feeling good). Ultimately, it’s the “liking” that we, well, like. It’s the sensation of pleasure we experience before anything else. We have to know that something feels good before we can want it, before a behavior can be reinforced or learned.
We like things for a reason that extends beyond the “liking.” There’s a biochemical component to pleasure, couched in the evolutionary drive to survive and reproduce and prosper. Thus, if hitting a squat PR, having great sex with your partner, and eating the bag of fat and protein and collagen known as a grass-fed beef rib make you feel warm and tingly, that’s probably a sign that those things are good for you, because our pleasure system was likely developed with those stimuli (lifting heavy things, sexual contact, animal fat and protein) in mind. Conversely, a gram of cocaine on a Saturday night, a hard drive full of every porn permutation imaginable, and a McRib might make you feel even warmer and tinglier, and they’ll certainly keep you coming back for more, but they are supraphysiological triggers of those same reward pathways and thus deserving of suspicion. Our reward systems likely weren’t developed to handle stimuli of that magnitude, because stimuli of that magnitude simply did not exist. Our reward systems developed for a reason: to reinforce behaviors that conferred a survival benefit.
How does it all work?
As neuroscientists are learning new things about the brain’s pleasure systems every day, it’s still a work in progress, but this is the basic gist:
Sensory data from touch, smell, taste, and sound travel to the sensory cortex, where they are interpreted in terms of magnitude. Was it a soft or a hard touch, a strong or a faint smell, a powerful or a mild flavor – that sort of thing. Strong sensations elicit lots of sensory cortex activity as seen in MRIs, while sensations of less magnitude elicit less activity. From the sensory cortex, the data is sent to various parts of the brain, including the orbitofrontal cortex (OFC) and a host of others. These are the “hedonic hotspots,” areas of the brain rich in opioid-and-cannabinoid-producing and opioid-and-cannabinoid-receptive neurons (PDF). The more a person reports liking a particular sensation, the greater these areas light up with activity when presented with data from said sensation. The OFC, it seems, is a hotspot where a lot of the initial liking happens. The ventral pallidum is another, perhaps the major, hedonic hotspot that has been shown to respond to “diverse human rewards from food to money.” (PDF) The VP receives data from a host of other brain reward areas, including the OFC, to which it applies “liking.” It is in this particularly hedonic hotspot that researchers think opioids and endocannabinoids effectively “paint” sensations with “hedonic gloss” to make them pleasurable to us. “Sweet” isn’t delicious if the hedonic hotspots don’t get their say in the matter.
Pleasure is also mediated and modified by context. Hunger is the best spice, after all, and there’s nothing quite so pleasurable as an ice cold glass of water when you’re parched on a summer’s day. If a sodium-replete rat is given a super-salty food to taste, there is no pleasure response in the brain. If a sodium-depleted rat is given the same super-salty food, it’s suddenly pleasurable (PDF). Thus, it’s not just the properties of the stimulus that determine the pleasure response, but also the physiological needs of the person responding.
What about dopamine?
Although it used to be viewed as the pleasure neurotransmitter, neuroscientists generally agree that dopamine is the driver of reward. It’s the neurotransmitter that creates “wanting,” not “liking.” Dopamine does not mediate sensory pleasure. Dopamine doesn’t make sex feel good. It just makes you want the sex. Or, with something like amphetamine, which increases dopamine, you “want” the drug even if you don’t “like” the feeling.
Now that we have a rudimentary understanding of how pleasure works in the brain, let’s look at some specific examples of how this neurochemistry plays out when we’re exposed to a pleasurable stimulus.
Food is perhaps the most fundamental trigger of pleasure circuits (and the most easily abused). Stephan from Whole Health Source and J. Stanton from Gnolls.org both have excellent takes on the food-reward system that pretty much cover it all. Go read them.
I probably don’t have to tell anyone this, but orgasm feels good. It’s an overpowering pleasure, an intense culmination that somehow marries anticipation with sensation. Sure enough, during male ejaculation, the (male’s) brain apparently lights up like a heroin user’s right after shooting up, indicating a major role for opioids. Neuroimaging studies on women during orgasm also reveal significant activation of the brain’s pleasure centers. I also don’t have to tell anyone why sex feeling good helps the survival of the species, nor why our brains would insist on making sex pleasurable.
You’ve all heard about the runner’s high, right, that euphoric, pleasant state of mind you can reach through intense exercise? It used to be assumed that elevated serum levels of beta-endorphins (an endogenous opioid) were responsible, until scientists realized that beta-endorphins are too large to cross the blood-brain barrier into the brain, where the “pleasant state of mind” generally resides. In order for endorphins to be responsible, it would have to be the endorphins that the brain itself secretes. Only problem? Doing a spinal tap to check the opioid content of brain fluid is highly unpleasant and not very practical for human subjects. Luckily, a team of German scientists figured out a non-invasive way to track the activity of endorphins in the brain. They used this method on runners who’d just completed an intense bout of endurance training and found that endorphins do increase in the brain after exercise, particularly in the runners who reported the most euphoria. These brain endorphins aren’t just there to make you feel good, either. They’re also necessary for the exercise-induced creation of new brain cells. Furthermore, it appears that voluntary exercise is key. Plodding on the treadmill with the trainer’s proverbial whip at your back might not have quite the same pleasurable (and brain-boosting) effect as going for a trail run through your favorite piece of wilderness.
Endocannabinoids play a role, too. They’re small enough to pass through the blood-brain barrier, and mice with a cannabinoid receptor deficiency in the brain run 30-40% less than control mice. In humans and dogs, exercise increases anandamide (an endocannabinoid) signaling throughout the body and brain. They say we’re “wired to run,” but really, we’re “wired to do things that make us happy.”
Touch is both utilitarian and pleasing. You use it to grasp the handle of the shovel, to tell you that you’ve just bumped into something, to differentiate between sharp and dull objects, and to shake hands, among other activities. But touch can also be sensual and pleasurable, and research shows the large myelinated nerve fibers that pick up on “rapid skin movement” (hard labor, grasping door handles, shaking hands, utilitarian stuff) are separate from the nerve fibers that pick up on “innocuous skin deformation” (stroking, caressing). In fact, the sensual fibers, known as c-tactile nerve fibers, activate the orbitofrontal cortex, the same place that responds to pleasant tastes and smells, as well as other areas of the brain known to be activated by opioids. The large myelinated fibers activate and inform the tactile discrimination function (the ability to differentiate sensory data received through touch), which is mediated through another area of the brain.
Touch also releases oxytocin, a hormone that helps lower stress, increase relaxation, and promote bonding. Oxytocin probably isn’t directly related to hedonic pleasure, but the attenuation of stress and the feeling of bonding with another person are a kind of pleasure – and certainly improve one’s survival fitness.
Lying in the sun, particularly when you haven’t seen any for awhile, is an intensely pleasurable experience. You’re warm, you’re relaxed, you can almost feel the vitamin D synthesizing. For all intents and purposes, reasonable sun exposure is a healthy endeavor the pursuit of which should be mediated by the brain’s reward system. And yet study after study indicate that sun exposure does not increase circulating serum opioids. What’s the deal here? Well, seeing as how opioids in the blood can’t really cross into the brain, all these studies tell us very little about what’s going on in the brain and thus triggering (or not) our pleasure centers. I was unable to find any studies that looked at brain opioid activity, but seeing as how the addictive nature of tanning is being seriously explored, and getting sun is subjectively pleasurable, I’m confident it too triggers the pleasure network in the brain.
After all, even when you try to fool experienced tanners with fake UV, they know the difference and prefer real UV. Something is making the sun rewarding. If I had to place a wager, I’d bet that it has to do with the proopiomelanocortin (POMC) gene, whose expression triggers the secretion of melanocyte-stimulating hormone (MSH, a hormone that darkens the skin and protects it from UV damage) in the pituitary and beta-endorphins in the brain. If sunlight can trigger the release of MSH via the POMC gene, perhaps it’s also releasing beta-endorphins in the brain to make you feel good and get more sun (and thus vitamin D). This hasn’t been explicitly tested, but it wouldn’t be a surprising result.
Studies indicate that opioid action in the brain precipitates the “chills” or “shivers down the spine” you get when listening to a particularly good song. Indeed, as the intensity of the chills increased, cerebral blood flow to the areas of the brain involved with reward and pleasure also increased. Wait, wait, wait – but music isn’t “natural.” Why do we respond so strongly to it? Well, music takes advantage of pleasure centers that evolved to respond to the babbling brook that promises fresh water, the cry of gulls that means the coast is near, the crashing waves that accompany the gathering of shellfish. You generally don’t get chills from listening to the sound of nature, but rather a warm, relaxed, soothing feeling. Those pleasant feelings are happening in the same brain that produces music-induced chills, probably through similar avenues.
You’ve probably noticed that the neurochemistry of all this pleasure stuff isn’t quite as ironclad as, say, the Kreb’s cycle. We can recreate the latter on a poster using arrows and legends and symbols and know that it’s an accurate representation of what’s going on in your body. We can’t yet make a neat picture of what happens in the brain to make sensations pleasurable, because the brain is plastic and the pleasure “center” is actually spread out over many different regions. It’s not a linear path. Heck, the guys who study this stuff for a living admit that many questions remain unanswered. However, what we do know is this: the actual physical manifestions of happiness and pleasure are not learned, but innate.
Or, as Kent Berridge (PDF), neuroscientist of pleasure (sounds like a great male stripper name, eh?), puts it, “Evidence so far available suggests that brain mechanisms involved in fundamental pleasures (food and sexual pleasures) overlap with those for higher-order pleasures (e.g. monetary, artistic, musical, altruistic and transcendent pleasures). From sensory pleasures and drugs of abuse to monetary, aesthetic and musical delights, all pleasures seem to involve the same hedonic brain systems, even when linked to anticipation and memory.”
In other words, we come equipped with a robust and complex reward and pleasure system(s) whose primary job is to keep us healthy, strong, fit, and above all, happy. Sure, as I mentioned last week, those systems can be hijacked by processed food, drugs, alcohol, tanning beds, and other hyper-stimuli to wreak havoc on our health and happiness, but the systems are not our enemies. If we use our better judgment, if we stop to think about why whatever we’re doing feels good and makes us happy, if we trust our intuition that things like bird songs, sunshine, the smell of dirt, and a babbling brook are good stimuli, I think we can actually use the reward/pleasure system for its intended purpose – to guide us toward smart choices that benefit our health, happiness and wellness.
Sorry, for the length on this one, folks, but the subject matter itself is a little dense. I hope you enjoyed it. Most importantly, I hope you learned a little something about why you like the things that you like, and why liking them isn’t just understandable, but absolutely necessary for health and happiness.
I’ll be covering how we can align our lifestyle behaviors with what our genes “expect” of us to live not only healthy and fit lives, but also happy, fulfilling, content and peaceful existences in the modern world, here on Mark’s Daily Apple and in my upcoming book The Primal Connection (due out first quarter 2013). Stay tuned and thanks for reading!