Phantosmia is the term that describes olfactory hallucinations. People often report smelling a burnt, oily, or metallic odor that is not there and is usually a very early symptom of Superficial Siderosis. Olfactory receptors in your brain transform the chemical signatures of scents into electrical signals (as opposed to physical nerve signals). An odor molecule binds to the olfactory receptors in the nasal mucosa that line your nostrils. This binding action triggers neurons to send messages to your brain. Your olfactory nerve(first cranial nerve) carries these signals directly to the frontal lobe.
Our brain categorizes odors into two categories: good and bad. Pleasant smells activate serotonergic systems to release oxytocin allowing us to feel good, happy, and satisfied. Foul smells activate the dopaminergic system, norepinergic system, and epinergic system. These systems kick in a fight-or-flight reaction causing a person to feel repulsed, bad, or upset.
Updated: October 31, 2020