Ultrasound Smell: Exploring the Possibilities and Limitations

Craig: imagine watching a cooking stream and actually smelling the garlic sizzling in the pan. that's the dream of digital smell. but a massive new deep dive into ultrasound technology suggests that while we can trick your eyes and ears, your nose might be impossible to hack. tech companies are racing to create ultrasound smell devices that blast sound waves at your brain to make you smell things that aren't there. it sounds like sci fi, but the science is hitting a brick wall. it turns out your face is filled with air pockets that block the signal, and your brain needs actual chemicals, not just vibrations, to smell like a rose. what's going on here, john?

Jon: yeah. this one, i'm super excited about. this is cool and also super scary. so, all they do is think of it like a smell remote control. so instead of releasing actual chemicals in the air, they use focused sound waves to directly stimulate the brain region smell, the olfactory bulb. so the research team, they developed a specialized ultrasound system operating at 300 kilohertz frequency, and that provides sufficient skull penetration. so the focal depth was set to approximately 39 millimeters with the ultrasound energy converging below the forehead. and they used a beam angle of about 50 to 55 degrees to limit the focal area specifically to the olfactory bulb. now, the system itself, they required mri guided placement. so it used scans of the subject's skull to precisely align the focal region with the olfactory bulb target. so this technical precision was crucial because the olfactory bulb measures only six to 14 millimeters in length while the ultrasound wavelength is five millimeters. so that creates challenges for spatial specificity. now, this is really cool. obviously, the the pinpoint accuracy that's needed for this, as it is right now, might not make it scalable. but what are your thoughts on this? are you scared about this? because it it can make you smell, clean oxygen air, like, oxygen rich air or, ozone or burning wood or things like that. so this is this the four d sensory thing that we're looking at that, that we've been waiting for, or what do you think?

Craig: well, they definitely want it to be because this is something they could easily hook up to your vr goggles and off you go, right, an ultrasonic device, versus actually having something else in the room that sprays, smells, and stuff. however, call me, you know, an old fashioned guy, but i don't want anybody shooting ultrasound at my head. specifically at my brain or areas of my brain. yeah. i don't know the long term effects of this, but let me put my skepticism aside. maybe we'll talk about it later. it's a really cool concept. they are hoping this works, this sensory brain hacking. i think of it as, yeah, sensory brain hacking. instead of sniffing a real flower, machine shoots a focus sound waves at the smell center of your brain to trick it into thinking you're smelling a flower. it's a final frontier in immersion. we have four k tvs for eyes, surround sound for ears. if this worked, we could revolutionize, be our gaming, even in movies and whatnot at home. you could even help cure, smell loss in patients, which would be interesting. fully immersive environments in the metaverse, which would be interesting walking through digital forest and actually smelling the pine, helping, patients recover, smell after illness or injury. digital perfume, sending a scent as a text message as an example. just thinking outside the box here. i'm a little concerned about it, but the application seem really, really cool. what about, for example this is another way where technology can go bad. you know? i don't wanna smell the kitty litter box. so i put on my, you know, no smell hat, and off i go. yeah. or it changes my smell that i'm not smelling what i'm working on. and i think, that might become an addiction. you know, a teenager goes into the room and they don't wanna clean up and it stinks. they just put on their ultrasonic thing and it smells like roses and

Jon: well, even worse is, like, the like, if you're like, trying to gather my thoughts here. so this could be used as far as so, like, where there's lots of smog and lots of air pollution and, but the problem is with any of this, with this, you're still inhaling those nasty particles regardless of what your brain thinks it's smelling. so that's what scares me.

Craig: yeah. and so that's just one, you know, negative situation. i mean, i understand, for example, i wouldn't mind having something. like, when i go to clean the kitty litter box, i'll flip this thing on, and, hopefully, it would, you know, smell like something else so i know i'm breathing it in. i still gotta do this job. yeah. but maybe i can take some of the unpleasantness away, while i'm doing it. that's all i do. that's that's just one example because i have cats, and other people probably have an example where they yeah. hey. if i go into the situation, maybe i go i gotta go clean the toilet or something after a situation and, you know, i do something like this of, you know, trying to put on a gas mask or something. yeah. so there are go ahead.

Jon: instead of messing with your brain, you could wear that dyson, that headphones with the air filter built in that, that goes right into your mouth. so, i don't get me wrong. i'm excited for the applications for this. i'm excited for where it's gonna go. i'm just worried about how it'll mess up your or if it'll mess up your brain.

Craig: so there are concerns about research and lack of evidence supporting some of this and some safety parameters around the ultrasound neuromodulation. so we'll have to see how that goes, and they're still having difficult targeting, different simulation part of the olfactory, bulb to create, unique senses and stuff. but, to me, that sounds like something they will, get over.

Jon: yeah. and to ensure safety, the team adjusted the ultrasound output to an order of magnitude lower than the intensity of transcranial focused ultrasound or tfas, used in medical applications while carefully angling the beam to avoid the optic nerve, which kinda scares me. so simulate the stimulation protocol involved five short high speed cycles at a frequency of 1,200 hertz. the researchers implemented auditory masking with music through airpods, and that was to eliminate placebo effects, ensuring subjects wouldn't distinguish different focal spots through sound alone, which is interesting as well. so i thought and there yeah. no. go ahead.

Craig: there's some skepticism. scientists say, you know, beyond just ultrasound delivery, the complex olfactory processing involves multiple brain regions working together in intricate patterns. simply stimulating olfactory bulb cannot recreate sophisticated neural networks required for meaningful scent experiences. not really sure what meaningful scent experiences mean, but it sounds like, you know, they have some scientific challenges to overcome to get, us smelling a rose, for example. maybe a meaningful is to identify that as, you know, oh, that's chocolate or that's, you know, a forest in the rain, what have you.

Jon: yeah. yeah.

Craig: so we'll have to see because, it says ultrasound stimulation cannot replicate these complex temporal patterns that are essential for a realistic scent perception, but we'll have to see. you know, the brain, computer interface, smell applications could extend beyond simple scent vision. virtual reality experience might benefit olfactory environments, creating more immersive environmental applications could include treating smell disorders or providing sensory substitution for individuals with olfactory impairments. we talked about a bunch of these things. so we'll have to wait and see whether this actually comes through or whether, you know, it's not gonna do anywhere near what we want it to do and it's gonna fail like all the other smell illusion stuffs in the past. what do you think, john?

Jon: yeah. this is interesting. i think, so here's my thought on this, and just to kinda put it into perspective. so the the nose has, i think, so there's two four hun 400, dimension let's call them receptors, like, so for your nostrils. right? so if you think about that as in the when it comes to neurotechnology. so that's a 400 dimensional information channel, right, which is potentially offered by olfactory stimulation. think of it like this. it matches the complexity of modern ai language models, which suggests that, bci could, could take the place of this, ultrasonic, ultrasound kind of stuff. so there's a lot of future potential here. i just wanted to bring it back because we cover a lot of brain computer interfaces. so there's a lot of potential there.

Craig: definitely a lot of potential. and just to maybe, elaborate on the problem so people understand it a little bit better, smell is a chemical, not mechanical. a scent happens when a specific module, which work i'm gonna call the key because this is a lock and key problem. when a specific module called the key hits a specific receptor called the lock, that's when a scent happens. so it's a combination of those things. ultrasound is just a vibration, and it can't replicate this complex chemical code needed to distinguish between coffee and wet dog. so my advice is if you see a kickstarter for digital smell, keep your wallet closed until you see peer reviewed proof that this is actually going to do what they say it's gonna do, but i am super interested in this.

Jon: yeah. me too.

Craig: so the verdict in biology is currently winning the war against technology on this one. but until we can figure out how to teleport chemicals into your nose, smell o vision, it might remain a gimmick. let me know what you think in the comments below. would you even want to smell the internet? we'll keep watching this story closely. let us know.