Anterior olfactory nucleus

The anterior olfactory nucleus (AON) is an early olfactory processing region located mainly within the olfactory peduncle (olfactory stalk), immediately posterior to the olfactory bulb. Despite its traditional name, it is not simply a compact nucleus; it has a cortical-like organization and is considered the most anterior cortical structure associated with the olfactory peduncle.

The AON receives olfactory information from the olfactory bulb, predominantly from tufted cells but also from mitral cells, through fibres travelling in the lateral olfactory tract. Rather than simply relaying this information, the AON participates in its early processing and modulation and has extensive connections with the olfactory bulb, piriform cortex, and other olfactory and limbic regions.

An especially important feature of the AON is its feedback to the olfactory bulb. It sends fibres back to both the ipsilateral and contralateral bulbs and communicates with the AON of the opposite side through the anterior commissure. These connections allow information entering through the two nostrils to be compared and coordinated, contributing to bilateral integration of smell and localization of an odour source. The AON may also regulate the strength of signals leaving the olfactory bulb—a process referred to as sensory gating.

Experimental studies further suggest roles in odour processing, social odour recognition, and linking odours with contextual memories. Much of the detailed functional evidence, however, comes from animal studies. In humans, the anterior olfactory nucleus is smaller and less continuous than in rodents. Rather than forming one continuous structure, its neurons occur as several clusters extending from within the olfactory bulb along the olfactory peduncle toward the forebrain.