by Aditi Mishra – In an annoying mystery, my lab mate Cheyenne’s coffee always smells better than mine. I tried emulating her coffee ritual – the same ingredients, the same cup and the same barista.
I even resorted to keeping my coffee where she usually does. All in the hopes of catching the right ‘microfluidic air current mumbo-jumbo’, so that the same ethereal smell would waft up my nose.
But to no avail! Her coffee still smells divine, while my coffee, well, smells like ‘coffee’. Every working day starts with a delicious aroma emanating from my neighbor’s cup – just out of my reach. What an agony!
Several iterations later I realized that the only difference was our timings. She was always a couple of minutes ahead of me, but the effect couldn’t be due to sensory adaptation either. We spaced our coffee apart and the annoyance remained.
Time to gulp down some bitter truth with some equally bitter coffee. For me the perceptual value of coffee was inversely proportional to its attainability. In other words, I was craving coffee but not really enjoying it. That was perplexing, why would you want something you don’t enjoy.
Only one way to find out – rapid hunched backed googling with fingers jabbing away at the keyboard. So google, what makes us crave thing we know we don’t enjoy?
Contrary to expectations, google shows this question is not trivial at all.
What is craving?
The dictionary defines craving as an intense desire, but there is more to it. Understanding craving requires a tiny bit of Zen. Take a deep breath and analyze your last craving. What makes something rewarding?
An object of desire should be at least one of these things – wanted, pleasurable or associated with pleasure.
Understanding reward via pleasurable associations is pretty intuitive. After all our lives are spent running after money – worthless bits of paper exchangeable for things of desire.
The difference between wanting and enjoying is bit more subtle.
Puzzle solving illuminates this difference. Most people hate solving the same Sudoku again but we hate unsolved mysteries too. This is because we ‘want’ to solve puzzles but it is the solutions that render them ‘pleasurable’. So we look out for new puzzles but an unsolved remains a heartache.
Wanting is motivating and energizing. It piques our interest. This is what drives us to try new things, a novel band for example.
Enjoying, on the other hand, is a satisfying continued indulgence. This is what drives us to keep the same song on a repeat.
If there existed a mythical land of rewards, wanting would be the force that propels individuals into its boundaries while enjoying would keep individuals from leaving. Wanting is the push to enjoyment’s pull.
Robinson and Berridge were the first to describe this difference in their incentive-sensitization theory. They coined the terms Incentive salience for wanting and Hedonic value for enjoying.
Objects are usually wanted and enjoyed. The difference becomes imperceptible because animals are good at forming associations therefore anything enjoyable becomes wanted.
However, there is a difference and it is more evident in the brain.
Neural pathways of desire
The brain computes wanting and enjoying using different circuits and different currencies.
Studies show that wanting a reward arises from a large, distributed brain network involving multiple regions of the brain while enjoyment is due to activity in a smaller set of specific hotspots in the limbic system. Some of these regions are ventral palladium (VP) and shell of nucleus accumbens (NAc).
In an elegant analogy, Berridge describes these enjoyment enhancing hotspots as “smaller Opioid Island” contained in “a large sea of ‘wanting’ opioid systems” in his 2009 review on brain substrates and eating disorders.
The differences extend well beyond the neural circuits. Even the neurotransmitters driving these reward systems differ.
Wanting increases when the neurotransmitter dopamine acts on the NAc, keeping enjoyment unchanged. While enjoyment increases when activators of opioid receptors act on NAc hotspots instead.
These nuances of pleasure have been elucidated by rats.
Rats that have lost almost all their dopaminergic neurons lose all motivation to eat, but as they are starving themselves to death they still enjoy the sweetness of sucrose.
In a sad parallel, patients suffering from severe Parkinson’s disorder, people who have lost most of their dopamine containing neurons exhibit the same thing.
Experiments on mice models have shown that the link holds true not just in deficiencies but in excess as well. Mice genetically engineered to have higher levels of dopamine show more “wanting” without any increase in signs of enjoyment. Now, how do we know if mice are enjoying themselves?
It turns out that enjoyment looks pretty much the same on mice and men. Among other things, human babies and mice lick their lips sideways while enjoying themselves. This constitutes “orofacial liking expression” or the readout for joy.
However these studies are only correlative. The only causative association unfortunately comes from an account of persecution.
In the 1950-60s, a young man was being treated for a slew of illnesses, his sexual orientation being one of them. As a patient of the psychiatrist Robert Heath, he was implanted with self-stimulating electrodes in the regions containing the nucleus accubens, or NAc. The electrodes certainly made him feel pleasured, alert and warm but all also made him intensely crave sex. They were never a substitute for sex.
This negates years of misconception. The idea of dopamine as the gateway to pleasure is flawed.
Higher dopamine levels in the shell of the NAc accomplishes just one thing – severe cravings. Enjoyment, it turns out is a different beast all together, one that requires activation of opioid receptor hotspots in NAc.
But the NAc does not work alone. The neighbor of the NAc – the ventral palladium (VP) – is instrumental for joy as well. Lesions in the anterior or lateral VP lead to an abolition of liking while infusing the same spot with opioids makes sugar sweeter. Rats lick their lips twice as fast and neurons of VP fire twice as fast when rats lick sucrose.
Interestingly, in rats with salt deficiency, the neurons of the VP spike twice as hard for a triple-seawater taste. Rats normally find salty solutions unpleasant, except in periods of salt deficiency. In times when rats find salt water appetizing, the VP finds it exciting too, the neurons respond to salt water like they normally would for sucrose.
So the ventral palladium seems to be the apparatus for liking. While the Nucleus accumbens seems to puppeteer our cravings.
What can incessant craving drive a person to?
In the Grecian mythologies, Tantalus, the gluttonous son of Zeus, is damned to eternal tormentation with delicious food and drinks held just out of his reach – much like my coffee.
But unlike me, his life was gravely miserable. Soon incessant cravings gave way to crippling anxiety in Tantalus.
A life of cravings does not come easy.
Innumerable Tantaluses walk amongst us – people fighting addiction – each day reminiscent of Tantalus’ misery. Food, alcohol, or prescription drugs – whatever their addictions may be, these battles are real.
Neural processes sometimes go awry. Within the brain of an addict one system might increase wanting due to increased sensitivity while tolerance in another reduces enjoyment. This forces addicts to do drugs they cannot enjoy.
This also explains why so many detoxes fail. While the circuits for hedonic value resets earlier, the circuits for craving drugs persist longer.
Understanding these circuits may someday alleviate the pangs of addiction, but today they might enable us to be just a little more human and empathize.
We often think of addicts as failures. We deem them selfish and blinded by pleasure. But these circuits tell us otherwise. Recovering addicts are normal people fighting cravings with a broken impulse control. Perhaps a little compassion could help them heal what is broken.
Berridge, Kent C., and Morten L. Kringelbach. “Pleasure systems in the brain.” Neuron 86.3 (2015): 646-664.
Pecina, Susana, et al. “Hyperdopaminergic mutant mice have higher “wanting” but not “liking” for sweet rewards.” Journal of Neuroscience 23.28 (2003): 9395-9402.
Smith, Kyle S., Kent C. Berridge, and J. Wayne Aldridge. “Disentangling pleasure from incentive salience and learning signals in brain reward circuitry.” Proceedings of the National Academy of Sciences 108.27 (2011): E255-E264.
Berridge, Kent C. “‘Liking’ and ‘wanting’ food rewards: brain substrates and roles in eating disorders.” Physiology & behavior97.5 (2009): 537-550.