27 September 2007 by jesni

By Morten Kringelbach (quarterly@dpu.dk)

We are all to some extent committed to the pursuit of happiness, but most of us only experience it fairly rarely. Even when happiness is present in a situation, we usually only discover it after the fact. This is because the human mind is quite often a regular 'troublemaker', as Dalai Lama recently said in a speech to a group of brain researchers. He admitted to feeling anger and fear himself from time to time, and suggested meditation as a remedy, but he was quite willing to discuss other paths to insight, such as neuroscience.

The research conducted by the TrygFoundation's Research Group at Oxford and Aarhus Universities is aimed to provide us some insight into pleasure and desire's functional neuranatomy in humans. The primary aim is to help people who lack happiness in their lives. Typical examples of this would be people who suffer from depression or eating disorders, where things that normally afford us pleasure suddenly lose their attraction; neither food, sex or other people's company gives a depressed person the same pleasure it would a healthy person - which unfortunately tends to drive the depressed even further into depression.

Neuroscientific research into well-being and happiness is still, however, a field in its infancy, partly because these states are very difficult to induce, unlike the closely related feelings of pleasure and desire, which are both easier to achieve.

Pleasurable patterns of behaviour
Pleasure has long been considered very difficult to examine scientifically, since it in many ways could be considered the epitome of subjectivity. However, pleasure is often accompanied by behaviour that signals our experience of something pleasurable: From smile and laughter in the company of happy friends to hoarse grunting in the throes of sexual pleasure. Many people would no doubt find that our pleasure would not be the same without these patterns of behaviour that are caused by pleasure.

It is even possible to enhance the feeling by using these pleasure-related patterns of behaviour consciously. This was demonstrated by an experiment where test subjects walked around for an entire day with a ball-point pen in their mouths. Half the test subjects held the pen sideways, so that they activated the muscles usually associated with smiling, while the others held it in such a way that it pointed straight ahead, like a cigar. The first group reported a heightened happiness and pleasure, most likely due to having been smiling the whole day, but perhaps also because the reactions they got from other people were genuinely funny.

These pleasure-induced patterns of behaviour are well-known from newborn babies, who lick their lips when they are fed sugar, and if you feed them something sour, they look angry. In time, these reflexes are dulled, and we gradually learn to hide our immediate responses to the food we get, even though it can be difficult at times. Rats and mice show similar pleasure-induced patterns of behaviour, but unlike humans, the rodents preserve these patterns throughout their lives. The higher a concentration of sugar you feed a rat, the more it will wet its lips. This makes lip-licking a useful measure of the degree of pleasure a rat experiences.

Pleasure and desire
The American neuroscientist Kent Berridge from the University of Michigan applied this knowledge in the design of a series of experiments that have provided us valuable insight into where in the brain pleasure is registered. While previous research has indicated that dopamine is released as 'reward' for something pleasurable, Berridge's research has shown something else. If dopamine really was the drug that gives us a sensation of pleasure, higher levels of dopamine should lead to an increase in our pleasure-related behaviour, but this turned out not to be the case. In fact, Berridge demonstrated that if the amount of dopamine in the brain is increased, rats and mice no longer lick their lips when the concentration of sugar in their drinking water is increased.

Rather, it turned out that the rats attempt to obtain the reward much faster than rats and mice that have not been tampered with. This would seem to indicate that dopamine plays a larger role for desire and need than for pleasure. If, on the other hand, rats are stimulated by opiates in a certain area of their brains, the frequency of lip-licking increases. It turns out that this part of the brain can best be described as a pleasure-map. Stimulating one sector of this map leads to a higher rate of lip-licking in response to the same amount of sugar in their water, while the response can be dampened by stimulating another part of the map. While the rat would normally lick its lips a few times, it will do it either much more or much less frequently, depending on which part of the map we stimulate.

Based on these findings, we can conclude that different parts of the brain and different neurotransmitters are involved in pleasure and desire, respectively. The dopamine system seems closer related to desire, while the opiate system is more likely to be connected to pleasure. All this of course while remembering the vast differences between humans, rats and mice. Rat brains are no bigger than a thumb, so the difference in scale alone is an important factor.

Pleasure and desire in humans are very complex emotions, and we are just scratching the surface so far. One part of the brain that is definitely of great significance is the orbiofrontal cortex, which is highly developed in humans, and which can control both the opiate and the dopamine systems in the brain.  This means that the orbiofrontal cortex plays a key role, but there are other important parts of the brain, a fact which makes the emotional brain something of a patchwork.

Room for dessert?
We examined the subjective pleasure of test subjects by means of the principle of 'selective full stomach'. Most of us are familiar with the feeling of having eaten a full meal, and yet we have room for dessert. We conducted a brain scan experiment, where we gave hungry test subjects tiny samples of chocolate milk and tomato juice. Then we removed them from the scanner and gave half of them tomato juice until they absolutely did not want any more (we stopped before they felt sick!), while the other half got chocolate milk. In other words, we induced a feeling of sensory fullness for either tomato juice or chocolate milk. We could measure this by observing that the first group of test subjects no longer felt any pleasure in drinking tomato juice, but it turned out that they still felt the same pleasure from drinking chocolate milk as they did at the beginning of the experiment.

The test subjects were then taken back into the scanner, and the experiment was repeated. The difference between the two runs was limited to the subjective experience of completely identical stimulation, and this enabled us to identify the areas of the brain connected to subjective pleasure. The experiment allowed us to correlate the test subjects' subjective assessments with the scannings of their brains throughout the experiment. In other words, we were able to pinpoint the areas in the brain where the brain activity corresponded to the subjective evaluations, and therefore probably represent the subjective experience of pleasure. We identified this type of activity in a region in the frontal part of the orbiofrontal cortex. This and later findings points to a series of interesting new potential treatments that may have a profound impact on our comfort and health. Right now it gives us a way to measure the lack of pleasure connected to depression and eating disorders, for example.

Pleasure without desire
The neuro-anatomy of pleasure is, in other words, still very much a mystery we have only just begun to unravel, but an understanding may perhaps be found by looking at the various components. What is the connection between desire, pleasure and happiness? Could it be that happiness is best described as pleasure without desire, as a stable feeling of satisfaction? Such a state is perhaps very similar to the blissful state that Buddhists attempt to achieve through meditation. If this is the case, neuroscientists may one day identify some means to induce this state. We could then have the choice whether to introduce a genuinely utilitarian society where the sum of happiness can truly be maximised, as suggested by the British philosopher Jeremy Bentham in the eighteenth century. It is, however, still an open question whether such a society would be desirable, or even comfortable.

In the final analysis, it is beyond doubt that we are very interested in the state of happiness, often much more in how to actually achieve that state. This was also the case for Dalai Lama, who spoke about how people have "many conflicting emotions, bad feelings, jealousy, anger, fear. These are our greatest troublemakers". He reminded the assembled scientists about the "fundamental value of mercy and love," which are "important for the development of both mind and body". When we meddle with the very core of that which makes us human, we must not forget this compassionate plea for human dignity.

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About Morten Kringelbach
Professor Morten L. Kringelbach, Dr.Phil., is an award-winning neuroscientist and author at the universities in Oxford and Aarhus, as well as the head of the TrygFoundation's Research Group, which conducts research into the human brain, pleasure, desire, emotion, learning and consciousness. Visit Morten Kringelbach's website

 

Morten L. Kringelbach

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