Conceptually well-being or happiness has long been viewed as requiring at least two crucial elements: positive affect or pleasure (hedonia) and a sense of meaningfulness and engagement in life (eudaimonia). The pleasure aspect is most tractable, and can be inspected against a growing background of understanding of the neural foundations for specific pleasures. However most would probably agree that eudaimonic happiness poses harder challenges to psychology and neuroscience. It is difficult even to define life meaningfulness in a way as to avoid dispute, let alone to tie a happy sense of meaningfulness to any specific brain patterns of activation*.

In studies conducted during the 1950s, Canadian psychologists James Olds and Peter Milner found that rats would repeatedly press levers to receive tiny jolts of current through electrodes implanted deep within their brains. When this brain stimulation was targeted at certain areas of the brain, the rats would repeatedly press the lever – even up to 2,000 times per hour. In fact, they would stop almost all other normal behaviors including feeding, drinking and having sex. Eventually the levers had to be removed to prevent the rats from starving themselves to death. The findings seemed to suggest that Olds and Milner had discovered the pleasure center in the brain. One of the main chemicals aiding neural signaling in these regions is dopamine, and so it was quickly dubbed the brain’s “pleasure chemical.”**

Similar studies in humans followed in 1960s. American psychiatrist Robert Heath conducted the ethically questionable experiments of implementing electrodes in the brain of mentally ill patients and his team even tried to find a cure for homosexuality. Although the researchers also found compulsive lever pressing in some patients (Patient B-19 in particular), it is not clear from these patients’ subjective reports that the electrodes did indeed cause real pleasure.

Recent work by Kent Berridge indicates that the electrodes may have activated the structural regions that are involved in desire rather than pleasure. When Berridge manipulated rodents’ dopamine levels, he found that although they did try to get to the reward much more quickly than normal rodents, their facial expression (an indication of hedonic pleasure) remained unchanged. From his earlier work, Berridge knew this is not what would be expected if dopamine really elicits pleasure**.

Berridge therefore proposed a distinction between the dual aspects of reward: hedonic impact and incentive salience. Hedonic impact is the liking or pleasure related to the reward. Incentive salience is the wanting or motivation for the reward. Finally learning is the associations, representations, and predictions about future rewards based on past experiences.

Extensive research has demonstrated that these different psychological components (wanting, liking and learning) are mediated by partly dissociable brain substrates as well as different types of neural transmitters. Dopamine is actually more closely linked with “wanting” than with “liking”, which instead appears to depend on the opiate system.

Whenever I can’t make it to the gym for a couple of days, I am just dying to get back to my workout routine.  That’s ‘wanting’.  As I exercise my body, my spirit is lifted, my mind gets sharper and I feel good about myself and life in general.  That’s ‘liking’.  Regular workout  enables  me to sleep much better and look more fit.  So I know it’s good for me, which provides the determination and motivation to incorporate it as a permanent part of my lifestyle.  That’s ‘learning’.  However  when ‘wanting’ grows over time independently of “liking” and “learning”, it becomes an addiction, such as the lab mice and alcoholics.

Some insight into pleasure-causing circuitry of human brains has been gained by affective neuroscience studies in rodents in which the hedonic hotspots are neurochemically stimulated to magnify a sensory pleasure, and so reveal the location and neurotransmitter identity of the generating mechanism for intense ‘liking’. The results of such studies reveal a network of several brain hedonic hotspots, distributed as a chain of ‘liking’ enhancing islands of brain tissue across several deep structures of the brain. One major hotspot has been found in the nucleus accumbens, a brain structure at the bottom front of the brain. The network of separate but interconnected hedonic hotspots acts together as a coordinated whole to amplify core pleasure reactions. At the highest levels, the hotspot network may function as a more democratic heterarchy, in which unanimity of positive votes across hotspots is required in order to generate a greater pleasure*.

Even though human brain possesses capabilities far beyond that of the animals, the recognition that hedonic brain mechanisms are largely shared between humans and animals allows application of conclusions from animal studies to a better understanding of human pleasure. The empirical evidence that both hedonia and eudaimonia co-occur in the same happy people opens a potential window of opportunity to the neuroscientific study of both aspects of well-being.

In the past few years, evidence has also grown to indicate that for humans, brain mechanisms of higher abstract pleasures strongly overlap with more basic sensory pleasures*. Does this mean that hedonia (e.g. shopping, playing computer games) and eudainomia (e.g. meditation, doing charitable work) essentially evoke neural signal that converge on the same brain circuits activated in Olds and Milner’s rats and in Patient B-19? And does it also imply that the pathways to higher pleasure may evoke more positive votes across the hotspots to generate greater sense of well-being and more meaningful learning?

It’s likely that in the coming years, more scientific evidence will emerge to support or amend the above preliminary conclusion. I think it’d be worthwhile designing an experiment to compare the brain activities of the people who laugh hysterically through tickling vs. through hearing funny jokes (substantial research has been done on how the brain processes jokes). The former is mainly direct sensory pleasure while the latter presents a much more complex task for the brain and therefore generates higher reward when one gets the joke or pun. If the above conclusion holds true, the same pleasure areas in the brain should light up to a much greater degree in both cases. But I am more interested in discovering how differently these areas are stimulated to spring into action.

When we are happy, either hedonically or eudaimonically, our brain learns and the circuits between neurons change when the brain learns. Desire and understanding are very closely linked. Desires make us smart, and without it, learning can be difficult.

*Building a neuroscience of pleasure and well-being by Kent C Berridge and Morten L Kringelbach
** The Pleasure Center by Morten L. Kringelbach