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Q&A: Predicting the Future by Smelling

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We all know certain smells can bring memories back to life. A christmas tree,  your grandma’s baking scents or your first brand of deodorant can take your mind straight back to other times. But these smells can also help us to predict the future, science shows. Marijn van Wingerden has found the part of the brain that makes this possible.

Marijn van Wingerden (1978) started studying cognitive neuroscience at the University of Amsterdam in 1997. Since then he (co-)authored 8 different neuroscientific publications. The last one, just published in Neuron, is about smells and learning in the rat’s brain. Van Wingerden currently works in Düsseldorf, as a postdoctoral researcher at the Heinrich-Heine University.

You found out how we can predict the future with smells, how did you do that?
We introduced rats to a variety of scents and let them decide whether or not to perform a certain behavior. The outcome of the behavior depended on the scent. Scent A for example meant a rewarding outcome, while scent B predicted a punishment. Then we turned these outcomes around and looked at the activity in the rat’s brain.

Rats are quite smart, so they adjusted to these new rules pretty quickly. This was also visible in their brain. The pattern of electrical signals, sent out by neurons, was very different when the presented odor was associated with a reward, than when it was associated with punishment. The neural activity patterns thus predicted what would happen after the behavior.

Does this say something about how we use smells to predict the future?
Humans don’t really use smell that much. Vision or audition is more important for us. But whether it’s a smell, a vision or a sound, these are just vehicles for information. We found out how this information is picked up and turned into unique neural patterns to predict outcomes of behavior: it’s done by neurons in the orbitofrontal cortex, just behind the eyeballs.

But there’s more. We also found out we could interfere with this predicting function of electrical patterns. When we blocked the so-called NMDA-receptors, that you can find everywhere in the brain, the rats did not adjust their behavior (completely) to new rules. We could also see that in this condition the patterns of different scents didn’t differ much.

So what can humans do with this new insight?
It opens doors for more research on some mental diseases. We for example know that people suffering from major depression or obsessive compulsive disorder have an impaired orbitofrontal cortex and have problems adjusting to changing rules like the ones in the rat experiment. We also know that ketamine, a drug that blocks the NMDA-receptor, causes schizophrenic experiences, including memory loss. It now seems these phenomena may be linked.

And can we now do something about smells that bring up bad memories?
The effect of the blocked NMDA-receptor only works just before, during or right after the actual association of a scent with an experience is made. With problematic bad memories, like those of people with post traumatic stress syndrome, it’s of course too late for that. But other researchers have shown that with exposure therapy we can relive the memory to change associations. Maybe blocking the NMDA-receptor can help with this.

But don’t forget that a lot of negative associations with smells are actually useful. We are for example born with a dislike for the scent of rotten eggs or unhealthy chemicals. We wouldn’t want to change that.

van Wingerden, M., Vinck, M., Tijms, V., Ferreira, I., Jonker, A., & Pennartz, C. (2012). NMDA Receptors Control Cue-Outcome Selectivity and Plasticity of Orbitofrontal Firing Patterns during Associative Stimulus-Reward Learning Neuron, 76 (4), 813-825 DOI: 10.1016/j.neuron.2012.09.039

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