Olfaction - Olfactory Coding and Perception

Olfactory Coding and Perception

How olfactory information is coded in the brain to allow for proper perception is still being researched and the process is not completely understood. However, what is known is that the chemical nature of the odorant is particularly important, as there may be a chemotopic map in the brain; this map would show specific activation patterns for specific odorants. When an odorant is detected by receptors, the receptors in a sense break the odorant down and then the brain puts the odorant back together for identification and perception. The odorant binds to receptors which only recognize a specific functional group, or feature, of the odorant, which is why the chemical nature of the odorant is important.

After binding the odorant, the receptor is activated and will send a signal to the glomeruli. Each glomerulus receives signals from multiple receptors that detect similar odorant features. Because multiple receptor types are activated due to the different chemical features of the odorant, multiple glomeruli will be activated as well. All of the signals from the glomeruli will then be sent to the brain, where the combination of glomeruli activation will encode the different chemical features of the odorant. The brain will then essentially put the pieces of the activation pattern back together in order to identify and perceive the odorant.

Odorants that are similar in structure activate similar patterns of glomeruli, which lead to a similar perception in the brain. Data from animal models, suggest that the brain may have a chemotopic map. A chemotopic map is an area in the brain, to be specific the olfactory bulb, in which glomeruli project their signals onto the brain in a specific pattern. The idea of the chemotopic map has been supported by the observation that chemicals containing similar functional groups have similar responses with overlapped areas in the brain. This is important because it allows the possibility to predict the neural activation pattern from an odorant and vice versa.