What is the Uncus?

L.K. Blackburn

The uncus, also called the uncinate gyrus, is a region of the brain made of white matter that is located on the tip end of the medial surface of the parahippocampal gyrus. It is part of the temporal lobe, which is situated at the bottom of the brain underneath the frontal lobe directly near the base of the brain stem. As part of the olfactory cortex, the uncus processes information from the sense of smell.

The uncus processes information related to scent.
The uncus processes information related to scent.

Most of the olfactory system of the brain is located in the nasal cavity and the frontal lobe of the brain, not as part of the temporal lobe. Frontal lobe and temporal lobe olfactory regions are connected by the olfactory tract and the anterior commissure. These nerves bring information stored on neurons to the uncus for processing.

The uncus is part of the temporal lobe.
The uncus is part of the temporal lobe.

Nasal cavities have a mucus membrane that collects sensory information in the form of axons that travels along the first cranial nerve to their first stop at the olfactory bulb. This region is part of the frontal lobe olfactory system. Once moved out of the bulb area, axons head to the uncus, which is part of the olfactory cortex. The two parts of the olfactory cortex are the hook-shaped uncus and another separate portion on the frontal lobe.

A head injury can cause damage to the olfactory nerve, resulting in losses in both taste and smell.
A head injury can cause damage to the olfactory nerve, resulting in losses in both taste and smell.

After transitioning through the uncus, further processing of olfactory information happens at the insular cortex. Smell and taste information is combined here to send signals to the brain for additional levels of processing, such as the perception of taste and flavor. When there is olfactory nerve damage from head injuries or tumors resulting in the loss of the sense of smell, taste is also usually impacted. Should seizures originate in this area, many individuals report first experiencing strange phantom smells. When the sense of smell is damaged, only one nostril may be affected because the nerve endings are separate for each.

The uncus is located directly on top of the amygdala, almost surrounding it. This area of the brain processes emotion and emotional memory. Many different parts of the brain communicate with the amygdala, including the olfactory bulb.

Increased size of the temporal lobe can cause an uncal herniation. The olfactory system often shows the first indication that there are any major issues with brain function. When this happens, the uncus presses down on a cranial nerve that is adjacent to the brain stem. Untreated, this can lead to central herniation and the possibility of coma and diabetes insipidus.

Uncal herniation may require surgery.
Uncal herniation may require surgery.

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Discussion Comments


@bythewell - I think it's interesting, of course, and wouldn't mind trying some of the effects of scent on the brain myself.

But I don't like the idea that advertisers can subtly affect me like that through scent. It feels almost like they are tapping directly into my brain and manipulating what they find.

They made it illegal to play movies with subliminal messages, why not do that with scent as well?

Of course, it's not quite the same thing, but I just feel like I need to be on my guard with everything people try to sell me, nowadays.


@irontoenail - Scent can affect your brain in even more ways than that. Scientists don't really understand it completely yet, although it makes sense, since it would have been a powerful survival tool when we were all living in the wild.

For example, smelling something nice makes you more likely to buy more. Which is why they pump baking cookie smells into car parks, and create signature scents for department stores.

It can also change your mood. They know that just smelling peppermint will actually make you feel more awake, for example.

It's kind of cool isn't it? I think that scent will be more incorporated into products from now on.


I've heard that the part of the brain that's responsible for processing smells, which obviously includes the uncus, is really close to the part of the brain which processes and stores memories.

That's why in most people scent and memory is so closely linked.

Like, the smell of, say roses, can vividly bring back a memory associated with the smell.

In fact, sometimes when I smell something it can bring back a memory I haven't thought of in a long time, or even just a feeling, which I think I probably used to associate with a memory that is now forgotten.

The brain can be a funny thing sometimes.

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