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Serge Ahmed

Last update Friday 05 July 2019

It takes two to reward

Serge H. Ahmed1,2

1 Université de Bordeaux, Institut des Maladies Neurodégénératives, UMR 5293, 146 rue Léo-Saignat, F-33000 Bordeaux, France

2 CNRS, Institut des Maladies Neurodégénératives, UMR 5293, 146 rue Léo-Saignat, F-33000 Bordeaux, France

The word “reward” has the same etymological roots as the French word “regard” from the verb “regarder” which meant “to ward against, guard.” Today, “reward” means recompense – récompense in modern French – as opposed to “punishment.” A reward is something used by someone (the rewarder) with the intent to reinforce a desirable behavior in someone else (the rewardee). “To reward” is also a transitive verb that describes the action of using a reward. One can also try to reward someone for not behaving in some undesirable way, but this typically does not work well which explains why one prefers in such case to resort to punishment. Thus, fundamentally, the concept of reward defines a specific relationship between at least two individuals (or groups of individuals). It takes two to reward: a rewarder and a rewardee. Examples abound. Parents reward their child. PIs reward their post-docs. Funding agencies reward scientists and academies do the same too. And, of course, we neuroscientists reward our lab animals, notably with the hope to decipher the brain mechanisms of reward. In each case, however, a different kind of reward is used: love; first-author position in a scientific publication; grant money; peer recognition; or palatable food. Clearly, what works well with some rewardees may not work with others. For instance, it is relatively easy to reward all kinds of behaviors in a mouse with a high-fat food pellet, but try using a high-fat food pellet to reward a post-doc. Differences in reward also exist across the sexes. And, of course, a same rewardee is differently sensitive to a given reward at different stages of her life and even at different times of the day, depending on fluctuating internal states. Thus, a reward is not inherently rewarding. How come?

Recent neuroscientific advances have revealed that a reward is rewarding in virtue of its ability to change activity in some specific structures of the rewardee brain, called variously since the 1950s “reward centers”, “reward pathways”, “reward systems”, “reward networks” and, more recently, “reward circuits” or even “reward circuitries.” What compose these brain structures at the molecular and cellular levels, how they develop and age through time, how they normally function or dysfunction in certain pathologies, how they compute and broadcast so-called reward signals in the brain, will be among the important questions that will be covered during the Conference. During my introductory talk, I will also emphasize another dimension that is often overlooked, but that is the elephant in the room. As already mentioned, it takes two to reward: a rewarder and a rewardee. Relatively recently in human history, this relationship has evolved into a novel variant in which a few rewarders get rewarded by rewarding frequently and potently a mass of rewardees, even if this generates addiction-related disorders and diseases in many. Some historians have aptly called our age “the Age of Addiction.” In this context, our increased knowledge and control of reward mechanisms in the rewardee brain, not only bring the promise of immense benefits to society, but also important risks, notably if this knowledge and control are exploited for the benefit of few at the peril of many. I will try to explain what these risks are and why we should ward us against them. Perhaps one way to resolve this issue would be to complement our sophisticated neurobiology of the rewardee brain with a neurobiology of the rewarder brain which remains to be invented.