Physicians at Massachusetts Eye and Ear have induced a sense of smell in humans by using electrodes in the nose to stimulate nerves in the olfactory bulb. The researchers say that their efforts, published in the International Forum of Allergy & Rhinology, provide a proof of concept for efforts to develop implant technology to return the sense of smell to those who have lost it.
“Our work shows that smell restoration technology is an idea worth studying further,” said corresponding author Eric Holbrook, MD, director of the division of rhinology at Massachusetts Eye and Ear and associate professor of otolaryngology at Harvard Medical School in Boston. “The development of cochlear implants, for example, didn’t really accelerate until someone placed an electrode in the cochlea of a patient and found that the patient heard a frequency of some type.”
Five patients (aged 43 to 72 years) with a history of sinus surgery, including total ethmoidectomy, with intact ability to smell were enrolled in the study. The ability to smell was confirmed with a 40-item smell identification test. Awake patients underwent nasal endoscopy and either a monopolar or bipolar electrode was positioned at three areas along the lateral lamella of the cribriform plate within the ethmoid sinus cavity. A graded stimulation current of 1–20 mA at 3.17 Hz was administered while cortical evoked potential recordings were collected. Subjective responses of perceived smell along with reports of discomfort were recorded. Participants with artificially induced smell underwent repeat stimulation after medically induced anosmia.
Three patients described sensations of smell (including reports of onion, antiseptic, sour, and fruity aromas) as a result of the stimulation.This was reproducible after inducing anosmia, but cortical evoked potential recordings could not provide objective support. All subjects tolerated the study with minimal discomfort.
The study authors say that the report opens the door to the development of what they call a “cochlear implant for the nose”—though they caution that the concept of an olfactory stimulator is more challenging than existing technologies.
“There’s currently so little that we can do for these patients, and we hope to eventually be able to reestablish smell in people who don’t have a sense of smell,” Dr. Holbrook said. “Now we know that electrical impulses to the olfactory bulb can provide a sense of smell—and that’s encouraging.”