Sensory Systems/Neurosensory Implants/Olfactory Implants

Olfactory Implants

Transversal cut of the head showing the olfactory bulbs.

Anosmia (Loss of Smell) appears in about 5% of the general population. An intact olfactory system is a core part of the perception of flavor with drinking and eating. Most problems presenting with taste loss come from an olfactory disorder. Additionally, the reception of smell is also central to our quality of life. Many experiences, such as a spring showers, fresh flowers or the scent of home add to any event, even if they are difficult to describe. While inflammatory causes of smell loss can be solved with the use of topical and systemic steroids, many treatments for other common causes of anosmia, including upper respiratory infection (URI), head trauma, and aging have not proven effective.

Inflammation of nasal mucosa can lead to anosmia.

Feasibility study

A Study by Eric H. Holbrook, Sidharth V. Puram and others was done to determine the feasibility of inducing smell through artificial electrical stimulation of the olfactory bulbs in humans. Five subjects (age, 43–72 years) were enrolled. Three subjects reported a perception of smell with electrical stimulation. All subjects tolerated the study with minimal discomfort. The test subjects were all able to perceive smell, which was confirmed with a commercially available, 40-item, scratch-and-sniff identification test. Under endoscopic guidance and without topical anesthetic, a monopolar or bipolar electrode was positioned at 3 areas along the lateral lamella of the cribriform plate at the junction with the skull base: (1) the anterior ethmoid posterior to the frontal sinus opening; (2) the posterior ethmoid anterior to the sphenoid face; and (3) the middle ethmoid approximated by half the distance between the anterior and posterior points. During 0.2-0.3ms, the implants were stimulated with an intensity range from 1 to 20 mA. 3 of the 5 subjects reported an experience of smell yet could not clearly state what that smell resembles and had differences among each other. The perception of smell did not change majorly with different intensities or electrode location, but small deviations described as “sweet,” “sour,” or “bad” were reported. There were no differences between monopolar or bipolar electrodes. The perceived smell was described as “onion-like,” “antiseptic like” or “sour,” and “fruity” or ”bad.” When asked to rank the perceived intensities of the smell on a scale from 1 to 10, the result ranged from 2 to 4. All subjects also experienced some discomfort with the devices, which presented as a throbbing, tingling, or pulsing sensation located at the ground electrode, the inner canthus of the eye or bridge of the nose, nasal tip, or in one case deep behind the eye. Electrodes that were positioned in the olfactory cleft caused sneezing or discomfort in four of the subjects and in the only one that tolerated it resulted in no perception of smell. In conclusion, the study achieved the perception of smell with electrical stimulation of the olfactory bulb for the first time. The authors plan to further explore the use of such implants, stating “Future work will extend the trials to include subjects without a sense of smell and develop more consistent objective measurements of olfactory perception.” This study was only intended as a proof of concept for future research into the possibility of restoring the olfaction from smell loss with electrical stimulation technology.