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1 Can other animals feel pleasure?

When your pet dog yelps excitedly as you throw a favourite toy, or your cat purrs contentedly as you scratch its head, you can’t help but wonder if they’re “enjoying” themselves. But are you just being anthropomorphic to suggest your pet has feelings?

Once a taboo subject, many researchers are now starting to consider the possibility that animals have an inner world of emotions. They experience fear, pain, joy and anger as well as more complex emotions such as embarrassment, love and grief, according to Marc Bekoff from the University of Colorado, Boulder, author of The Smile of a Dolphin (Weidenfeld & Nicolson, 2000). As for pleasure, Bekoff is in no doubt that animals experience it. Animals at play, for example, appear to be having fun.

Bekoff points to work by Jaak Panksepp, a neuroscientist from Bowling Green State University in Ohio, who discovered some years back that infant rats, when they play or when they’re tickled, make regular high-pitched noises just as if they were laughing. Their behaviour suggests that they’re experiencing pleasure, says Panksepp. When accused of anthropomorphism himself, he points out that animals at play produce opioids, the brain chemicals that are increasingly being seen as the main mediators of pleasure in humans. And the brain systems and genes that control the rats’ behaviour are equivalent to those in people. Although we can never prove they feel pleasure, he says, “there is overwhelming evidence for the conclusion that they do.”

Physiologist Michel Cabanac of Laval University in Montreal, Canada, is similarly convinced that there is feeling associated with animal emotions. “We have good reasons to accept that reptiles experience pleasure,” he says.

If you place a lizard in an enclosure with a warm lamp in one corner and food in the opposite, cold corner, when it really needs to eat, it will venture quickly into the cold. It deals with the conflict of motivations by trading off different needs. So where does pleasure come into it? By slightly changing the conditions, Cabanac believes he has shown that the lizard’s choices are guided by relative pleasure and displeasure. “Pleasure shows what is useful to an animal,” he says.

This time he placed normal food in the warm corner and the lizard equivalent of gourmet food in the cold corner. The lizards ventured out to eat the gourmet food as long as this part of the enclosure was above a certain temperature, but when it got too cold they stayed in the warm and just ate the nearby food. The better the food in the cold corner, the lower temperature the lizards will tolerate. They trade off food quality and warmth. It cannot be a reflexive behaviour, such as simply ceasing to move because of the cold, Cabanac claims. The lizard makes a decision based on palatability. “This means they must experience palatability, or pleasure,” he says.

In another experiment he showed that lizards can learn to avoid food with a particular taste that once made them sick. Mammals do this easily, and people stop liking food that made them sick. In other words the process is driven by experiencing pleasant and unpleasant sensations. “So if it takes place in lizards, it seems likely that they also know sensory pleasure,” says Cabanac. When he carried out the same experiment on frogs and toads they did not learn to avoid foods that made them sick, suggesting that pleasure evolved around the time reptiles branched off from amphibians. “Frogs and toads, I believe, are just robots,” says Cabanac, “whereas reptiles have a mind.”

Neuroscientist Antonio Damasio from the University of Iowa also thinks animals have pleasure, though he’s not sure they’re aware of it. He believes emotions and feelings are two distinct things – emotions are physiological processes that help guide behaviour, whereas feelings come from experiencing and reflecting on those physiological processes. Animals, he says, definitely have emotions – even a fly can be happy or angry. But do they feel them?

In Damasio’s model, feelings require a complex brain capable of representing the animal’s body. We know that humans have sophisticated sensory maps of the body in cortical regions of the brain, in which emotions trigger different patterns of neural activity. These patterns are what produce feelings, thinks Damasio. Other primates certainly have sensory maps, though it’s not known exactly what kind of body maps other animals have, nor what level of sophistication would be needed for feelings to emerge.

2 Is there a limit to pleasure?

Yes, says George Koob, neuroscientist and addiction expert from the Scripps Research Institute in La Jolla, California. The pleasure system, he reckons, is like a bank. Take out too much money too quickly and you’ll simply run out, or worse, you could go bankrupt – the route to addiction. So why can’t we have it all, all the time?

You have to consider what pleasure is for, says Koob – a reward system that guides our behaviour, giving us a simple way to decide what to do next. Pleasure acts as a kind of common currency, allowing us to compare the relative values of behaviours such as feeding, drinking, mating or relaxing, according to what our body needs at the time.

But for pleasure to work in this way, it must have built-in limits, thinks Koob. If an animal gets too carried away with the pleasure of eating something, it is likely to fall prey to the next predator that comes along. Pleasure has to be transient enough to let us focus on the next task. “I think there’s a reason for the brain being created to limit pleasure,” says Koob. “If it wasn’t, then the species would be compromised in some way.”

Koob believes the brain puts a limit on pleasure in two ways. The first is the simple depletion of dopamine, opioids and other mood chemicals such as serotonin. You can see this happening in a cocaine binge, he says. Once dopamine levels drop, for example, so too does the motivation to continue taking the drug.

The second way is through the brain’s stress system. According to his model, pleasurable experiences stimulate the stress system, with stress chemicals being released and feeding back to limit the amount of pleasure we feel. The combination of dopamine depletion and stress build-up is a powerful limit to pleasure, he says.

This tight regulation creates what he calls a “hedonic set point” – your baseline level of pleasure. Get a pay rise and you may feel good for a while. But you don’t stay pleased for long. If you win the lottery, move to an idyllic home and give up work, in the long term you won’t necessarily be much happier. Pleasure seems to be superimposed on a baseline you always return to.

But if you misuse your pleasure system, you may start to have trouble rising above this baseline. That’s part of the process of addiction, says Koob. At first a drug may be intensely pleasurable, but the pleasure resources are quickly frittered away. Now the same amount of drug produces a smaller pleasure response. And because the brain’s reward system is depleted, you get no pleasure from anything but drugs. Addicts spend most of their time not trying to experience bliss but just trying to feel normal, says Koob. Eventually even drugs won’t do it. It’s as if they’ve bankrupted the system. The changes in the brain can be incredibly long-lasting, perhaps explaining why addicts can relapse after many years of abstinence.

Koob sees people using up their pleasure resources in all kinds of addiction-like behaviours. Whether you’re a workaholic or binge eater, or experience an unhealthy compulsion to have sex, go shopping or gamble, the limited resources of your pleasure system are being expended too rapidly.

Take compulsive running, says Koob. At first people run for pleasure, but once they have crossed a certain threshold, being unable to go running makes them miserable, irritable, depressed and withdrawn until they can run again. They are no longer running for pleasure, but to avoid the pain of not running.

You could attain pleasure all the time, but it’s not going to be intense pleasure all the time, says Koob. There’ll never be designer drugs to give “free” highs or hour-long orgasms without somehow having to pay the costs later. Evolution has made the eternal high impossible – too much pleasure would simply distract us from the nitty-gritty of surviving.

The other bad news is that there’s no limit to displeasure. “Displeasure indicates what is harmful or dangerous,” says Michel Cabanac of Laval University in Montreal, Canada. And unlike pleasurable stimuli, the unpleasant stimulus may be ever-present. If the source of danger or pain is not removed, the displeasure remains. Only joy is transient.

3 Can pleasure be unconscious?

If you’re happy and you know it, clap your hands. So goes the children’s song. But can you be happy and not know it? Can you have pleasure without being aware of it? Surely, by definition, you experience pleasure and so must be conscious of it?

Not necessarily, says neuroscientist Kent Berridge of the University of Michigan. He reckons pleasure can sometimes be an “implicit emotion” – a state that can alter how we behave or think, but that we can have no awareness of, even upon introspection.

He points to experiments that show how pleasure-inducing drugs can alter people’s behaviour without their experiencing any conscious pleasure. In one example, the late Marian Fischman of Columbia University and the New York State Psychiatric Institute gave cocaine addicts the choice of pressing two levers. One delivered a high dose of cocaine, the other a lower dose. The addicts were free to give themselves a series of shots and, after experimenting, they repeatedly chose the higher dose. The researchers gradually lowered both doses, to the point where the addicts’ heart rates and adrenaline levels no longer respond to the drug. By now the subjects insist there is no drug. But given the choice, they still choose the undetectable cocaine more frequently than an empty shot. They say they are picking at random, and are unaware that they favour one over the other. Without their knowing it, the tiny dose is guiding their behaviour.

Berridge and his colleague Piotr Winkielman, a psychologist now at the University of California, San Diego, found that if they showed people subliminal images of happy or angry faces they could induce pleasure without their subjects being aware of it. They flashed images of happy or angry faces onto the screen for just 16 milliseconds before showing a neutral face for much longer, so the subjects were only conscious of having seen the neutral image. Immediate questioning showed they experienced no obvious mood changes and didn’t feel any different. But if they were thirsty, they would drink more after subliminally viewing a happy face than an angry one, and rated the drink as more pleasant-tasting, more attractive and worth more money, even though all the drinks were identical. This, says Berridge, is implicit emotion – liking without feeling.

4 Why is music pleasurable?

It’s easy to see how pleasure might have evolved to help us choose between vital behaviours. But why do we find pleasure in more abstract things such as art, music or winning money? Emotionally charged music clearly taps into the same brain regions as other pleasurable stimuli. Anne Blood and Robert Zatorre from the Department of Neuropsychology at McGill University in Montreal, Canada, used PET scans to show that emotional “chills” induced by music activate the same brain regions as euphoria-inducing stimuli, such as food, sex and recreational drugs. But how?

We can learn by association that a particular stimulus predicts we’re about to receive another that we naturally find pleasurable. For example we can use money to buy food, and we enjoy food, so by association we learn to find pleasure in money. But how could that work with a piece of music?

Neuroscientist Jaak Panksepp from Bowling Green State University in Ohio believes something different is happening. He suggests that music taps directly into the innate pleasure systems. “Music makes baby birds respond, it makes cows give more milk,” he says. Rats, mice and chickens all get the musical chills too. Music must be affecting our emotions at a very basic level.

He believes it triggers brain mechanisms that originally evolved to make mammals and other animals respond to their crying offspring. “Separation” calls can induce a slight drop in temperature in the parents, perhaps the origin of the musical chill. And when parent and child are reunited, chemical changes occur in the brain that look very like other pleasure responses, releasing opioids and other neurochemicals.

5 Why do we feel high after something stressful?

Why do people go bungee-jumping, throw themselves over steep cliffs on snowboards, or jump out of aeroplanes? How can something dangerous or stressful give a buzz of pleasure afterwards? Thrill-seeking, according to researchers, is simply a by-product of how our brains work.

Our pleasure system is there to reward us and guide our behaviour, making sure we are doing things that will help us survive. But some types of beneficial behaviour naturally involve risk-taking, points out neuroscientist George Koob of the Scripps Research Institute in La Jolla, California. Foraging, hunting, competing for a mate – these can be incredibly risky. Being safe and finding what we need are often in conflict. If pleasure guides our behaviour, so taking risks sometimes ought to be pleasurable too. “Something can be both stressful and pleasurable,” he says. “Stress can be rewarding in itself.” Stress hormones – cortisol in humans, corticosterone in rats – produce a transient “high”, says Koob. Corticosterone is a modest stimulant and activates the dopamine system.

But to be useful in guiding behaviour, pleasure shouldn’t last too long. An animal that becomes too distracted by the pleasure of eating is very likely to get eaten itself, which could partly explain why if you eat too much, what tasted pleasant begins to become unpleasant and may even make you feel sick. Koob thinks the counter-response to bring us back down after a buzz of pleasure is also mediated by stress. Stress activates a brain system as well as a hormonal one, inducing release of corticotropin releasing factor and noradrenaline and depletion of neuropeptide Y, all of which help to restrain our feelings of pleasure.

In effect, the stress and pleasure systems are antagonistic, making our feelings swing back and forth like a pendulum. This means every emotional high has to be followed by a low – but also that every low has to be followed by a high.