Smell and Taste

Smell and taste are chemosenses, that is, they are sensory systems that respond to chemical stimulation and whose chemical stimuli bind to receptors to create a sensation. Both are two of the most neglected and unusual in the sensory panoply in that each exhibits features that uniquely and dramatically separate it from the dominant senses of vision and audition, and even somatosensation. For example:

Olfaction is the only sense with receptors directly exposed to the environment;

Humans have an ability to detect hundreds, if not thousands, of different odours but only five or so tastes. However, the same humans are notoriously poor at identifying such odours;

There is no agreed classification system for odour; there is more agreement for taste;

Unlike vision, hearing and touch there is no olfactory dimension that relates stimuli to sensation; it has no predictable frequencies nor limited spectra (Mackay-Sim and Royet, 2006);

Also unlike vision and audition, the olfactory system requires a third of the genome; vision requires three genes; audition requires a structure that develops from genes coding for other aspects of development (Mackay-Sim and Royet, 2006);

The olfactory cortex has three layers, unlike most other sensory cortices;

Taste and smell receptors regenerate every sixty days – thus, our current chemoreceptors did not exist two months ago;

Smell is probably the most manipulable and confusable of the senses: people can be convinced that an odourless substance is odorous or that they are smelling something they are not;

Taste is invariably confused with smell although smell provides the greatest contribution to food flavour;

Olfactory dysfunction may be a better marker of risk of degenerative disease (e.g. Alzheimer’s Disease (AD)) than more conventional neurophysiological or clinical measures.