“very absent-minded persons in going in their bedroom to dress for dinner have been known to take off one garment after another and finally to get into bed, merely because that was the habitual issue of the first few movements when performed at a late hour”

It is difficult to kick a habit. Like riding a bike – once automated, some behaviors can stay with us for a lifetime. Life-long memories are a familiar trait. After all, they define who we are. We can recall important events in our lives in sometimes astounding clarity and detail. In the last 40 years, neuroscience has made great progress in understanding how the brain accomplishes this amazing feat. Sometimes after a single exposure to a salient stimulus, synapses in the brain can permanently alter their properties to encode complex, vivid memories. If synaptic plasticity is so fast, why does it take practice to learn how to ride a bike, why repetition to form a habit?

The ultimate, evolutionary causes for the need to practice our skills are obvious. Skills and habits convey an enormous benefit as they free up processing power and allow us to efficiently carry out often-used behaviors with little effort. The repetition required to automate these behavior buys us time to pick the best sequence of movements to do the task. Without the need for practice, we may be stuck with whatever movements we used when we first tried to master the skill, often unsuccessfully. There must have been strong selection pressure on the neurobiological mechanisms (the proximate causes) which would allow for rehearsal time before behavioral memory was actually consolidated. One could think of any number of mechanisms which would slow down memory formation, from inefficiencies or delays in the intracellular processes altering synaptic transmission to initially weak reinforcement signals, scaling with the increasing success of the behavior. Yet, evidence from our ow experiments with the fruit fly Drosophila points to a different mechanism, namely dynamic interactions between multiple memory systems. We founsd that the memory system responsible for habit formation is temporarily blocked by the memory system dealing with learning about our environment. Interestingly,  switching off a part of the fly brain called the mushroom-bodies halved the amount of practice required to form habits, suggesting that the mushroom-bodies are involved in this blockage (as they are not directly involved in memory storage, they most likely mediate the interaction coming from the environment-memory storage system).

Now, almost simultaneously, two groups have published research that another treatment, stress, can lead to rapid habit formation in rats and humans as well. In almost identical experiments, the subjects were either stressed or not during operant conditioning experiments. In these experiments, the subjects had to perform two actions for two different kinds of food. After training, one of the two kinds of food was given to the subjects until they were sated. This feeding to satiation is the critical part of the experiment. Imagine you would like to eat a treat and a machine would make you work for salty or sweet treats. Obviously, when you've had as much sweets as you wanted, you'd work harder to get the salty treat than the sweet treat. What research into habit formation has shown, is that this specific reduction after devaluation no longer occurs when the training has taken place long enough to form a habit. Both animals and humans then just keep working the machine to get noth treats in equal number. Just placing the animals/people in front of the machine makes them follow their habit, similarly to the absent-minded people in former times who got undressed and went to bed, just because they were in their bedroom at a late hour. These two studies now showed that the two groups (stressed and unstressed) differed in their specific reduction after devaluation: the stressed groups behaved as if they had been trained for much longer and habitually worked the machine equally hard for both treats, even after relatively short training.

One of the authors of the study is my esteemed colleague Rui Costa, who I'm currently writing a grant for organizing a conference on actions and habits with. In a recent article in The Scientist he said: Thus, Rui also emphasizes the adaptive value of habits, to reduce cognitive load and allow the brain to focus on the more pressing issues and not how to best execute a behavior. The amount of training required to form a habit is flexible and reflects the trade-off between behaving flexible and behaving efficiently. If need be, we can form habits just as fast as we can learn facts, faces or events. (see also PhysOrg)

In a more colloquial formulation of the flexibility/efficiency (or exploration/exploitation) dilemma, one could say that habit is the enemy of creativity. It was German ethologist Konrad Lorenz who postulated that creativity requires a so-called "relaxed field" in which no stressors apply. Now, about three decades later, the biological experiments are being initiated to find out how the brain operates to give rise to this requirement.
Creativity is also a necessary prerequisite for doing innovative science. This means that stress is the enemy of good science. In our publish-or-perish culture with it limited contracts and constant fear of joblessness and failure, I wonder how many excellent scientists fall by the wayside, because they were never able to fulfill their full potential? Does this research argue for small, managable research groups in which there is a lot of time for interaction, free-thinking and relaxed brain-storming, rather than large, high-throuput labs in which everybody is just a cog in a large machinery producing scientific data, rather than doing science? Could this sort of research help us design the environment which maximizes on the brain capital of the individual scientists? Or will it just eventually lead to a treatment which enhances the blockade of habit formation, extending it indefinitely, no matter how stressful your life is, such that you will become for ever creative?

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• Schwabe, L., & Wolf, O. (2009). Stress Prompts Habit Behavior in Humans Journal of Neuroscience, 29 (22), 7191-7198 DOI: 10.1523/JNEUROSCI.0979-09.2009
• Dias-Ferreira, E., Sousa, J., Melo, I., Morgado, P., Mesquita, A., Cerqueira, J., Costa, R., & Sousa, N. (2009). Chronic Stress Causes Frontostriatal Reorganization and Affects Decision-Making Science, 325 (5940), 621-625 DOI: 10.1126/science.1171203
• Brembs, B. (2009). Mushroom Bodies Regulate Habit Formation in Drosophila Current Biology DOI: 10.1016/j.cub.2009.06.014