Amy Fleming in More Intelligent Life:
The reward system exists to ensure we seek out what we need. If having sex, eating nutritious food or being smiled at brings us pleasure, we will strive to obtain more of these stimuli and go on to procreate, grow bigger and find strength in numbers. Only it’s not as simple in the modern world, where people can also watch porn, camp out in the street for the latest iPhone or binge on KitKats, and become addicted, indebted or overweight. As Aristotle once wrote: “It is of the nature of desire not to be satisfied, and most men live only for the gratification of it.” Buddhists, meanwhile, have endeavoured for 2,500 years to overcome the suffering caused by our propensity for longing. Now, it seems, Berridge has found the neuro-anatomical basis for this facet of the human condition – that we are hardwired to be insatiable wanting machines.
If you had opened a textbook on brain rewards in the late 1980s, it would have told you that the dopamine and opioids that swished and flickered around the reward pathway were the blissful brain chemicals responsible for pleasure. The reward system was about pleasure and somehow learning what yields it, and little more. So when Berridge, a dedicated young scientist who was more David than Goliath, stumbled upon evidence in 1986 that dopamine did not produce pleasure, but in fact desire, he kept quiet. It wasn’t until the early 1990s, after rigorous research, that he felt bold enough to go public with his new thesis. The reward system, he then asserted, has two distinct elements: wanting and liking (or desire and pleasure). While dopamine makes us want, the liking part comes from opioids and also endocannabinoids (a version of marijuana produced in the brain), which paint a “gloss of pleasure”, as Berridge puts it, on good experiences. For years, his thesis was contested, and only now is it gaining mainstream acceptance. Meanwhile, Berridge has marched on, unearthing more and more detail about what makes us tick. His most telling discovery was that, whereas the dopamine/wanting system is vast and powerful, the pleasure circuit is anatomically tiny, has a far more fragile structure and is harder to trigger.