Rhinencephalon

The rhinencephalon is a ventral subdivision of each cerebral hemisphere of the telencephalon, corresponding to the olfactory region of the brain. It is named due to the relationships of its rostral parts with the olfactory apparatus.

During embryonic development, the rhinencephalon differentiates from the telencephalon, which itself arises from the primary prosencephalic vesicle of the anterior neural tube.

The rhinencephalon is divided into three parts:

• Basal part, which includes the olfactory bulb, olfactory peduncle, olfactory tubercle, and piriform lobe.

• Septal part, with the subcallosal area, the septum, and several gyri.

• Limbic part, which includes, among other structures, the hippocampus.

The rhinencephalon interacts with the cerebral cortex and the telencephalic nuclei to integrate sensory and emotional information and coordinate appropriate behavioral responses. It thus constitutes a central region of the limbic system, involved in emotions and olfactory memory.

In domestic mammals (and even more so in humans), the rhinencephalon represents a relatively small part of the telencephalon compared to the neopallium.

Based on the development of the basal part of the rhinencephalon (associated with olfaction), mammals can be classified into three groups. Carnivores, ungulates, glires, and rodents are considered macrosmatic species, with a highly developed olfactory region. Primates (including humans), pinnipeds, and most cetaceans are microsmatic, while delphinids are anosmatic, as these structures are completely regressed and have lost their function.