Olfactory Implants to Restore Smell: Where to Stimulate?

OBJECTIVES: To evaluate the viability of different anatomical targets within the olfactory system for electrical stimulation by an olfactory implant aimed at restoring smell. DESIGN: Narrative review of research relevant to olfactory implant development, with emphasis on stimulation feasibility and elicitation of olfactory percepts. MAIN OUTCOME MEASURES: Surgical accessibility, functional specificity, interindividual structural variability and olfactory perception responses to electrical stimulation across different sites within the olfactory system. RESULTS: The olfactory epithelium is the most surgically accessible target but is limited by factors including age-related degeneration and interindividual variability. The olfactory bulb, a major site of convergence in olfactory processing, has shown spatially specific percepts in animal models and reproducible percepts in early human studies. Recent studies have explored multiple surgical approaches varying in invasiveness and safety. Stimulation of structures in the central olfactory system, such as the piriform complex and orbitofrontal cortex, has produced occasional and non-specific olfactory or chemosensory percepts in epilepsy monitoring and deep brain stimulation. Non-invasive and extracranial stimulation strategies remain experimental with minimal validation in living humans. CONCLUSION: Current evidence suggests that the olfactory bulb is the best-suited target for future olfactory implant development. Its role in early olfactory processing, emerging surgical approaches, and early human feasibility make it the most viable candidate for restoring olfactory percepts.