A hearing aid for … your nose?

(Press-News.org) Kaboom! The first time most of us hear the sound of an explosion is in the movies. Encountering the sound in the real world—even at a distance—has a profoundly different effect. Why? It’s all about context. How we react to sounds and other sensory stimuli depends on how they’re presented. We often don’t know how we’ll respond to something until we experience it. And the sensation is sometimes quite different from what we expected. So, the brain has to adjust quickly.

Cold Spring Harbor Laboratory (CSHL) Professor Florin Albeanu explains: “In nature, animals are faced with different rules of engagement. Sometimes, the same stimuli mean different things depending on context. Therefore, it’s not so unusual that you have to act on these different rules and assess what action you have to take. What are the associations that the stimulus has with certain outcomes?”

New research from Albeanu and postdoc Diego Hernandez Trejo helps explain how this works. Their findings point to never-before-seen fast-updating signals in a feedback loop between the brain’s olfactory cortex and olfactory bulb. These signals may help put odors and sounds into new contexts. The feedback loop may enable an animal’s brain to immediately adapt to changes and help the animal fine-tune its motor responses accordingly.

Hernandez Trejo and colleagues ran a series of behavioral tests to measure mice’s reactions to different smells and sounds. The mice were trained to associate rewards with one stimulus but not the other—and only for a while. Importantly, the researchers switched the rules once the mice seemed to learn them. That presented little trouble for expert mice, Albeanu says. “The animal is able to extract this change. Within a few seconds, it’s going to act in a way that is consistent with understanding. Interestingly, we observed that top-down signals, which originate in the olfactory cortex, convey information about the reward value of the stimulus to the olfactory bulb—irrespective of them being sound or odor.”

The olfactory cortex is the part of the brain that processes smell, yet it seems to take sound into account. This result tracks with another CSHL discovery, which shows how sensory cues become integrated with each other in the brain. It also raises some exciting questions.

How do reward signals emerge? Does this feedback loop also integrate sight and touch? “There’s a universe of possibilities,” Albeanu says. He’s eager to continue exploring that universe along with collaborators Andrei Ciuparu and Raul Muresan from TINS in Romania, knowing that each answer tells us more about the world we share and the perceptions that shape our understanding of it.

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