Sight, sound, and touch are the senses we are the most aware of. Yet, the more primitive senses of taste and smell are in many ways equally essential to survival. Now, if you spend a few minutes observing dogs meeting in the park or a pet mouse wandering around the living room, you may be reminded of the importance of smell – recognizing food that is palatable, nutritional, and safe.
While olfaction may have evolved as a mechanism for evaluating whether a potential food is edible, it also has come to serve important social and marketing functions. Just think of the endless display of perfumes and colognes that line the first floor of every department store – a coincidence ? I think not.
Anatomical and lesion studies indicate that the primary olfactory cortex is located in the ventral region of anterior temporal lobe. After compiling the results of imaging studies, it seems that an intimate relationship between smelling and sniffing exists. Indeed, subjects were scanned while they were exposed to either nonodorized, clean air or one of two chemicals, vanillin or decanoix acid. You can all guess that the first smell is of vanilla, but any idea what the latter one is ? Well it’s a chemical that smell like crayons.
The odor-absent and odor-present conditions alternated every forty seconds and, throughout the entire scanning session, the instruction – “Sniff and respond, is there an odor ?” – was presented every eight seconds. In doing so, the researchers sought to identify the brain areas associated with sniffing or smelling.
Surprisingly, the results of this study suggest that the primary olfactory cortex might be more part of motor system for olfaction. Yet, upon further study of the primary olfactory cortex in the rat, this phenomena became clear. The studies with the rat have shown that these neurons habituate quickly. Which means that each sniff represents an active sample of the olfactory environment, and that the primary olfactory cortex plays a critical role in determining if a new smell is present.
The importance of sniffing for olfactory perception is explained by the fact that our ability to smell is continually being modified by changes in the size of the nasal passages. In fact, our nostrils switch back and forth, with one larger that the other for a few hours and then the reverse. Why would our nostril behave this way ?
Well, one hypothesis is that olfactory perception depends not only on the intensity of the odor but also on the efficiency with which we sample the odor. As a result, the brain is provided with slightly different images of the olfactory environment. Also, asymmetrical representations are the rule in human cognition, perhaps providing a more efficient manner of processing complex information.
Want to see where I got some of my information ?
Cognitive Neuroscience, The Biology Of The Mind, Second Editon, Michael Gazzaniga
The Sniff Is Part of the Olfactory Percept, Joel Mainland – click here