What Are the Mammillary Bodies?

Andrew Kirmayer

The mammillary bodies are two structures, the medial mammillary nucleus and the lateral mammillary nucleus, found on the underside of the brain and considered parts of the limbic system. Both are linked to the hypothalamus via a nerve path called the fornix and feature a series of neural projections that connect to other parts of the brain. The mammillary bodies are also a relay for signals that travel from the hippocampus and amygdale to the thalamus, a system called the Papez circuit. They are important to memory processing, so damage caused by either physical destruction or nutritional deficiencies can lead to amnesia.

Mammillary bodies are linked to the hypothalamus and are important in memory processing.
Mammillary bodies are linked to the hypothalamus and are important in memory processing.

Both the lateral and medial mammillary nuclei have connections to both the hippocampus and thalamus, carried by nerve fibers through the fornix. The nuclei connect with the same parts of the brain, although each is linked to differing sections of the same structures. They also have different functions, as the medial mammilliary nuclei has cells that fire according to the direction someone is facing and how fast the head moves. There are also cells that do this in the thalamus and the hippocampal area.

Hypoxia due to sleep apnea may cause damage to the mammillary bodies.
Hypoxia due to sleep apnea may cause damage to the mammillary bodies.

The medial nuclei of the mammillary bodies are comprised of one to five subnuclei depending on the type of animal, while the lateral mammillary nucleus contains the largest neurons in the system. Cellular signals for head motion and angle in the lateral nucleus are relayed to the hippocampus, which generates a theta rhythm that is important for spatial memory. Cells in the medial mammillary nucleus fire in the same pattern as those in the hippocampus, and the mammillary bodies seem to relay this rhythm to other areas.

Damage to the mammillary bodies leads to amnesia. The study of memory loss due to such damage or from a deficiency in thiamine was studied in the late 1800s and is known as Wernicke-Korsakov syndrome. Amnesia characterized by a loss of memories following a traumatic event is common with this condition, but long-term memories might be unaffected. Lesions in this area and other parts of the limbic system are often found in people that are chronically amnesic, and hypoxia due to sleep apnea can cause damage as well.

The mammillary bodies form a crucial component of the brain’s circuitry. Integrally connected to other areas of the brain, biologists thought they were another section of the hypothalamus. Memory, recognition, spatial awareness, and interpreting the context of events are affected when the area is damaged or dysfunctional.

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Discussion Comments


I have to describe the functions of mammillary bodies in my assignment. So far, I wrote down these: that they receive and send impulses through the Papez Circuit. That they help in the formation of recognition memory and make a connection between memories and scents. And that they also have to do with some reflexes like swallowing.

Have I missed anything?


@turkay1-- I'm very sorry to hear about your Grandma. I'm afraid I can't completely answer your questions as I'm not an expert on the subject.

I do know however that this condition is very common with alcoholism. It has been shown that excessive and long term use of alcohol leads to thiamine deficiency and eventually the degeneration and shrinkage of the mamillary bodies.

I think that there are some cases where this degeneration can be temporary, with dietary based thiamine deficiency perhaps. Supplementation might help to some degree but if the damage advanced, the memory loss will be permanent.

When you speak to the doctor, make sure to ask the exact stage in which the disorder is at currently. That is, how far has the degeneration gone in the mammillary bodies and what can be done at this point. Best of luck.


My grandmother was recently diagnosed with Wernicke-Korsakov syndrome. She seemed fine when I talked to her several weeks ago and then suddenly, I got a call from my brother saying that Granny has been hospitalized and they are running some tests on her.

The doctor said that due to heavy alcohol abuse, the mammillary bodies in her brain have been damaged. They have been giving her some thiamine supplementation and keeping her in the hospital for now. She seems utterly confused though. She had trouble remembering me and my brother and even tried to refuse medical treatment. It's hard to even get her to listen to what we're saying and we really don't know what to do.

Has anyone's relatives suffered from this syndrome? How did you cope and care for them? What kind of treatments are possible for this syndrome?

We have a follow up with the doctor in a few days but I'm just trying to get as much information as possible right now.

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