Function of the Olfactory Cortex

A disorder named 'Anosmia' or the absence of the sense of smell, is said to have affected about 2 million people in the US. A major cause for this disorder could be a serious injury to the head, leading to damage to the olfactory nerves as they enter the olfactory bulb. Another possible cause is damage to the frontal lobes resulting from a tumor or surgery.

Olfaction is the sense of smell. It includes the detection and perception of chemicals suspended in air. It is possible to perceive a smell or odor, with the help of your nose (when these chemicals enter) and your brain (to which the signals are transmitted). The sensory system used for sensing smell is the olfactory system.

It is known that sensory networks have corresponding areas in the brain for receiving and processing information, and for smell and odor input or signal, it is the olfactory cortex that is responsible. In other words, it is responsible for receiving and processing the signals for the identification and awareness of specific smells and odors.

Usually, signals from the other senses are initially processed in the thalamus. However, information from the receptors is directly received by the olfactory cortex.

Close to the limbic system, the olfactory cortex is situated at the base of the frontal lobe and medial aspect of the temporal lobe.

The olfactory cortex plays an important role in the receiving and processing of sensory information for the identification and awareness of odors.

Once the smell or odor is detected by the olfactory receptors, the signals are transmitted to the olfactory bulbs (located on the bottom side of the brain). These transmissions are further passed on to the olfactory cortex. Here the information is processed and further transferred to the thalamus by projections.

In the thalamus, the processed information is incorporated with the information coming from the other senses (vision). Most of the projections from this cortex move to a lobe named insular cortex, where the olfactory and the sense of taste signals are combined for additional levels of processing like taste and flavor.

The olfactory cortex is linked to the amygdala (a part of the limbic system that perceives emotional behavior and memory) by other neuronal connections. It is this connection with the limbic system that causes a smell or odor to trigger intense feelings and memories in a person. This happens even before the smell or odor is identified.

It is said that in cases of unpleasant odors, an increase of blood flow to these areas has been detected on brain scans, thus, depicting the active processing of information in the olfactory cortex.

In some cases, problems may arise due to the position and action of the olfactory cortex. The portion of the olfactory cortex on the temporal lobe that covers the area of the uncus may cause two conditions; uncinate fits and uncal herniation. Seizures that may originate in the uncus, often commence with an individual hallucinating a disagreeable odor.

Conditions such as tumor, hemorrhage, or edema tend to put pressure on the uncus, causing it to push against certain cranial nerves which may result in problems related to sensory input and movement.