Sensory networks in the body generally have corresponding areas in the brain dedicated to them. The olfactory cortex is the area responsible, in many animals, for receiving and processing smell-related, or olfactory, input. Located near the limbic system, just below the cerebrum, this region is the site where the majority of signals related to smell are processed. Its purpose and location contribute to some of the symptoms that are seen in disease states affecting the cerebrum, which is the largest area of the brain.
With other senses, signals are first processed in the thalamus, but the olfactory cortex receives information directly from receptors. Olfactory receptors in the nose send signals to the nearby olfactory bulbs, just beneath the frontal lobes of the cerebrum, and these transmissions are then relayed to the olfactory cortex, or lobe. Information may then be processed, and projections send this data to the thalamus, where it can be integrated with information from other senses like vision. Many of the projections from this cortex go to another lobe, called the insular cortex, where neurons integrate olfactory signals with those pertaining to the sense of taste. This area accounts for the close relationship between the two senses.
Other neuronal connections link the olfactory cortex to the amygdala, a part of the limbic system involved in the perception of emotions, as well as memory. Strong associations between smell and memories can result from this particular network. Additionally, emotional and behavioral reactions to smell are linked to the projections that allow this cortex to interact with the amygdala and the thalamus. When an unpleasant smell is detected, brain scans have revealed that blood flow increases to these areas, showing that they are actively processing information.
At times, medical conditions can arise that are closely linked to the actions and unique position of the olfactory cortex. Certain chemical compounds, as well as electrical signals, are capable of causing seizures due to the presence of a trigger zone, called the uncus, that is located in this region. Often, seizure activity that begins in this area can begin with an individual hallucinating an aversive smell. Tumors that put pressure on the uncus can also cause this region to press against certain cranial nerves; this can lead to a variety of consequences for sensory input and movement, in a condition called uncal herniation.
