The Jacobson organ, also known as the vomeronasal organ (VNO), is a chemoreception organ found in the nasal cavity of many animals. It functions as an auxiliary olfactory sense, assisting in the detection of specific chemical cues. Discovered by Frederik Ruysch and Ludwig Jacobson, it is typically located in the nasal septum. Its presence and capabilities across species, including humans, are subjects of ongoing scientific investigation.
How It Functions in Other Animals
The Jacobson organ plays a well-established role in the chemosensory systems of many animals, including snakes, lizards, and various mammals. It detects non-volatile chemical compounds, such as pheromones, which are signals exchanged between individuals of the same species. These cues influence behaviors like reproduction, social interaction, and territorial marking.
When these chemicals bind to VNO receptors, sensory messages are sent to the brain, often triggering a behavioral response. For instance, in some mammals, pheromone detection through the VNO can elicit the “Flehmen response.” During this, an animal curls its upper lip and opens its mouth, directing liquid-borne chemical particles to the VNO for analysis. This mechanism allows animals to gather detailed chemical information, contributing to their survival and reproductive success.
Anatomical Evidence in Humans
In humans, anatomical structures believed to be remnants of the Jacobson organ are observed, particularly during fetal development. The VNO appears during embryonic stages as an outgrowth from the nasal sac. While present in the embryo, its development in humans is often underdeveloped compared to other tetrapods.
In adult humans, some individuals exhibit microscopic pits or ducts on the nasal septum, sometimes identified as the VNO. These structures are typically located in the anteroinferior portion of the nasal septum. However, the existence of a fully formed or functional VNO in adult humans remains a subject of scientific discussion.
The Debate Over Human Function
The scientific community widely debates whether the Jacobson organ in humans retains any functional capacity. While anatomical remnants are sometimes observed, many researchers consider the human VNO to be vestigial and non-functional.
A significant argument against its functionality is the apparent lack of clear neural pathways connecting these structures to brain regions typically associated with sensory processing. Unlike in animals where a direct connection to the accessory olfactory bulb is observed, such a robust connection has not been consistently demonstrated in humans. The absence of a well-defined accessory olfactory bulb in adult humans further supports the notion that the organ may not process chemical signals in the same way it does in other species.
Studies attempting to link human behavior to vomeronasal stimulation have generally yielded inconclusive results. Despite some articles suggesting its presence and supporting its function, the prevailing scientific understanding indicates that the human Jacobson organ does not play an active role in detecting pheromones or influencing behavior.
Distinguishing From Other Chemical Senses
The proposed function of the Jacobson organ differs significantly from human smell (olfaction) and taste (gustation). Traditional olfaction detects airborne volatile compounds, processed by olfactory sensory cells in the main nasal chambers.
In contrast, a functional Jacobson organ would detect non-volatile, moisture-borne chemical signals, such as pheromones. These signals are typically not consciously perceived and would operate distinctly from airborne scents or orally consumed substances. This separate mechanism highlights the unique nature of the vomeronasal system as a potential chemosensory pathway, focusing on subtle, often unconscious, chemical communication.