We Induced Smells With Ultrasound

Summary

We pointed an ultrasound probe at the scent-processing region of the brain to obtain different sensations. Different focal spots corresponded to different smells, which we’ve replicated first-try on two people and validated with a blind trial. The sensations we obtained are: The sensation of fresh air, with a lot of oxygenThe smell of garbage, like few-day-old fruit peelsAn ozone-like sensation, like you're next to an air ionizerA campfire smell of burning wood Here is a video from our blind tasting: Your browser does not support the video tag. The Setup Smells are processed in the olfactory bulb. We decided to try to stimulate it with focused ultrasound through the skull. As far as we know, no one seems to have done this kind of olfactory stimulation before - even in animals. However, after being able to induce sensations of motion the previous week, it seemed promising to try the same for olfactory. The Anatomy The olfactory bulb, our target, is tucked behind the top of the nose. That turns out to be a pretty inconvenient location for a couple of reasons: The nose doesn’t provide a flat surface for mounting a transducer for stimulation. It's mostly filled with air, which interferes with ultrasound. Ultrasound needs a continuous medium to travel through, and filling the nose with gel seemed rather unappealing. Instead, we found that you can place the transducer on the forehead and aim the ultrasound downward towards the olfactory bulb. While this isn’t a perfect solution because the frontal sinuses can weaken the signal, careful device positioning above the sinuses still allows us to reach our general target region. The ultrasound We got our first effects using just a handheld probe and some gel, but it quickly became obvious that holding a probe steady by hand makes it nearly impossible to keep the focal spot in the same place. To improve stability, we improvised a makeshift headset, allowing for more reliable positioning. We switched from gel to a solid, jello-li...