Functional Ultrasound (fUS) Imaging Sniffs Out How Mice Smell

On these images, the cerebral activation detected by ultrasound imaging is shown in red. During odor presentation, specific areas are activated in the olfactory bulb but not in the piriform cortex. Credit: © Mickael Tanter / Hirac Gurden

Ever wondered how our brain processes the information coming from the nose? A waft of bacon in the morning or the smell of a guilty dog’s deeds on a fresh white carpet are both uniquely unmistakeable in our world of billions of smells. For a while, scientists have understood the organizational structure of the olfactory system, but have struggled to understand its function.

Now, researchers from Institut Langevin and Laboratoire Imagerie et Modélisation en Neurobiologie et Cancérologie (CNRS, Université Paris Diderot, Paris, France) have found a technique to use ultrasonic plane waves to image the functional brain at a high spatial and temporal resolution to see the blood volume changes in 100 micrometers at a 500 Hz frame rate.

When mice were stimulated with certain smells, the blood flow to specific parts of their main olfactory bulbs increased, indicating that neurons within the bulbs were activated in a spatial distribution (thus pulling in more blood flow due to higher cellular activity). This verified the results found by teams using optical imaging and fMRI techniques. The researchers also probed deeper into the brain with ultrasonic waves and found that the piriform cortex, a structure downstream of the olfactory bulb, did not have a spatial distribution response. The scientists speculate that the piriform cortex could have a more global role in integrating and storing smells into memory.

Functional ultrasound offers the advantages of low cost, ease of use, and high resolution. The team plans to continue the research to study the effects of learning on cortical activity in order to elucidate its role and understand the specificities of the olfactory system.

Press release: Ultrasound tracks odor representation in the brain…

Study in NeuroImage: Functional ultrasound imaging reveals different odor-evoked patterns of vascular activity in the main olfactory bulb and the anterior piriform cortex…