While distinct, the senses of smell and taste collaborate to shape our perception of what we eat. This partnership creates the rich and complex sensations we identify as “flavor.”
How Smell Works
The sense of smell, or olfaction, begins with airborne chemical molecules called odorants. These odorants enter the nasal cavity and interact with specialized olfactory receptor neurons located in the olfactory epithelium, a patch of tissue at the top of the nasal cavity. Each olfactory neuron expresses a specific type of receptor that binds to particular odorant molecules.
When odorants bind to these receptors, they trigger electrical signals. These signals travel from the olfactory receptor neurons through the cribriform plate to the olfactory bulb at the base of the brain. The olfactory bulb then relays this information to various brain regions, including the piriform cortex for odor identification and the thalamus, which acts as a relay station for sensory information.
How Taste Works
Taste, mediated by the gustatory system, involves detecting chemical compounds called tastants that are dissolved in saliva. These tastants interact with taste buds, which are small sensory organs primarily located on the tongue, but also found in other parts of the mouth like the throat and epiglottis. Each taste bud contains numerous taste receptor cells that have microvilli extending into a taste pore.
There are five universally recognized basic tastes: sweet, sour, salty, bitter, and umami (savory). When tastants bind to receptors on these cells, they trigger signals in nerve cells that send along cranial nerves to the brainstem, then to the thalamus, and finally to the gustatory cortex, where taste perception occurs.
The Creation of Flavor
Flavor is a multisensory perception. It is primarily the brain’s integration of signals from both taste and smell, alongside other sensory inputs like texture, temperature, and sound. The most significant contribution from smell to flavor comes from retro-nasal olfaction.
During chewing and swallowing, volatile odor molecules travel up the back of the throat into the nasal cavity, stimulating the olfactory receptors. This retro-nasal pathway allows the brain to combine these aromas with the taste signals from the tongue. For example, a strawberry’s “taste” includes its sweetness and the volatile compounds detected by retro-nasal olfaction. This integration happens in higher-order brain regions such as the orbitofrontal cortex, insula, and anterior cingulate cortex, creating the unified perception of flavor.
What Happens When the Connection Weakens
When the connection between smell and taste is disrupted, flavor perception is altered. When one has a cold or a stuffy nose, food often seems bland. This occurs because congestion blocks the retro-nasal pathway, preventing odor molecules from reaching the olfactory receptors, even though the taste buds are still functional.
Aging can also diminish both the sense of smell and taste, leading to a reduced perception of flavor. As people age, there can be a decrease in taste buds and olfactory nerve endings. Conditions like anosmia (complete loss of smell) or dysgeusia (altered or distorted sense of taste) demonstrate this reliance. Individuals with anosmia may perceive basic tastes but lose nuanced flavor profiles. Dysgeusia can cause everything to taste metallic, bitter, or sour, severely impacting food enjoyment.