Anterior olfactory nucleus


The anterior olfactory nucleus '' also called the anterior olfactory cortex, is a major early processing area for olfaction located behind the olfactory bulb, and in the olfactory tract. The AON connects the olfactory processing centres of both hemispheres.
It is involved in the sense of smell, and has influence on other olfactory areas including the olfactory bulb and the piriform cortex. The AON is one of the major secondary structures of olfaction.

Structure

The AON is found behind the olfactory bulb and in front of the piriform cortex and olfactory tubercle in the olfactory tract or retrobulbar area. The peduncle contains the AON as well as two other much smaller regions, the ventral and dorsal tenia tecta.

Function

The AON plays a pivotal but relatively poorly understood role in the processing of odor information.
Odors enter the nose and interact with the cilia of olfactory receptor neurons. The information is sent via the olfactory nerve to the olfactory bulb. After processing in the bulb the signal is transmitted caudally via the axons of mitral cells, and tufted cells in the lateral olfactory tract. The tract forms on the ventrolateral surface of the brain and passes through the AON, continuing on to run the length of the piriform cortex, while synapsing in both regions. The AON distributes the information to the contralateral olfactory bulb and piriform cortex as well as engaging in reciprocal interactions with the ipsilateral bulb and cortex. Therefore, the AON is positioned to regulate information flow between nearly every region where odor information processing occurs.

Components

The AON is composed of two separate structures:
  • a) a thin ring of cells encircling the rostral end of the olfactory peduncle known as "pars externa",
  • b) the large "pars principalis", seen in coronal sections of most mammalian brains as a two-layered structure.
  • * The deepest is a thick ring of pyramidal and other-shaped cells surrounding the anterior limb of the anterior commissure.
  • * The outer, cell-poor layer, is often subdivided into a superficial zone and a deeper area.
  • * Many divide pars principalis on the basis of the 'compass points,' yielding pars dorsalis, pars ventralis, pars medialis, pars lateralis, and pars posterioralis.