Although studies into the structures is causing some scientists to question human understanding of them, mammillary bodies primarily act as relays for impulses that travel through the brain. Additionally, the bodies appear to be very important in forming and recalling memories. Destruction or injury to these portions of the brain is often associated with amnesia.
The mammillary bodies combine with the diencephalon to form a portion of the limbic system. The mammillary bodies form the terminals of the anterior arches of the fornix. They carry electrical impulses from the brain and thalamus through to the spinal cord and on to the rest of the nervous system. This explains why these structures are often associated with sensory control and movement.
The mammillary bodies each contain two sets of nuclei. One set is called the medial nuclei, and the other set is called the lateral nuclei. Despite long-held beliefs about the mammillary bodies and their functions in memory, a 2010 study in “Neuropsychologia,” by SD Vann, found that the two different sets of nuclei have different functions. While Vann did not investigate the lateral mammillary bodies, Vann did find that the medial nuclei were important for spatial memory development and recall in rats.