The fact that Olfactory systems and areas in the brain evolved early on is because these systems are wired into our first Primitive Amphibian brain for survival. Smell is vital for our survival and not just for other animals but for homo sapiens too. If you look at the evolution of smell and the brain areas around this one sense called the Olfactory bulb in the limbic system, it is an ancient system and so very important for instinctual survival. The sense of smell was overtaken by the sense of vision in our evolution and this occurred when homo sapiens began to walk upright on two legs. If you smell smoke or gas you take prompt action, Smell plays an important part in selecting a partner for sexual selection through emotional attractions, and the Amygdala in our limbic system plays a huge role in how we choose, friends and partners, along with smell itself plays a huge role in what we choose for food and drink.All these factors are of such importance in the roles of our hereditary ancestral DNA.
Although humans can smell odors at a concentration as low as one part per trillion, our sense of smell is weak compared to compared to that of other animals. The size of the surface area of the Olfactory epithelium and the density of the smell receptor cells indicate how sensitive animal sense of smell is for example in dogs. They can identity a particular human just from a few odor molecules. Northern dogs such as jackals huskies, are renowned for their sense of smell. They do not take time to distinguish prey from background smells and go purely by instinct, as these systems of amygdala exist in their systems too, and it is all about survival of the organism.
Smell Preferences
Whether we find a smell nasty, nice, or neutral is very subjective and dependent on DNA of the Olfactory system. It is dependent on familiarity, intensity as perception of pleasant or unpleasant. It is not clear if preferences are innate or learned, as it suggest in research it is learned. Associated learning links pleasant smells to pleasurable experiences and vice versa. For example people who fear the dentist do not like the clove like smell of eugenol which is used in dental cement. Those without fear of the dentist react positively to this odor.
Stereoscopic And Blind Smell
Generally it is believed that the homo sapien sense of smell has atrophied in relation to other senses, but recent research shows that humans can still effectively track a scent using both nostrils to sample a smell the human brain uses both senses of data to accurately pinpoint the location of the source of the odor. Therefore as with vision and hearing sound, smell can be “stereoscopic” relying on both nostrils for a full understanding of a scent. Blind smell refers to the ability of the brain to detect a smell without being consciously aware of it which has been demonstrated in experiments using fMRI scans showing how Olfactory areas are activated without without the participant’s knowledge. This research also in scans shows the participation of the thalamus. Only two synapses separate the Olfactory system from the Hippocampus, and only two synapses separate the Olfactory system from the Amygdala. Olfactory nerves carries the signals from the Olfactory bulb closely linked to the hippocampus and the Amygdala. The Olfactory bulb in the limbic system close to the amygdala the almond shaped emotion machine in the limbic system and the hippocampus associated with memory when you first encounter a smell. It becomes linked to the Amygdala, the emotion in the limbic system, associated with the event of the time. Encountering the smell again may trigger this whole linked system of smell, emotion and memory paths with the memory of past experience.
In smell and memory an event is associated with an event of all the senses for example, smell, emotion and memory, all associated together, coordinated into a patterned memory in the hippocampus. Re-experiencing any of the sight, smell, or sound, can trigger a whole pattern of associated memories in the hippocampus. This may be because Olfactory regions are linked to all emotional areas in the limbic system. Research shows that a memory of a visual image is likely to fade within days, but the memory of a smell may linger up to years or even decades. Research shows that the hippocampus might not even be crucial for this link to occur, because people who sustain damage to this region can still recall scents from their childhood even though they might suffer from memory loss. Male sweat may contain androstenone a musky compound. When sprayed on a chair in a waiting room, women chose this chair to sit in. Women are more sensitive to this smell than men, even more when they are ovulating when they can pick up one part per trillion.
The Madeleine Effect
The Madeleine effect is named after an episode of Marcel Proust’s epic, “A Memory of Things Past.” As a mature adult the novel’s hero eats a Madeleine soaked in lime blossom tea and is mentally transported to his childhood, and the house of his aunt who use to serve Madeleines before Sunday mass. Long before the event was investigated scientifically, Proust recognized that taste and Olfactory memories can take us further back in memories than visual or auditory cues.
Smell and Communication
Animals emit compounds called pheromones that are used as a communication signal and detected by an accessory olfactory system in the brain. Humans recognize each other in similar ways – for example babies recognize their mother through smell because babies prefer the smell of their mother’s breast, rather than other women’s. Research into human pheromones has found that women’s menstrual cycles can synchronize when one woman is exposed to odorless compounds (supposing there are pheromones emitted from underarm of another woman. In animals the accessory of the olfactory system is linked to the vomeronasal region (VMO) an area in the nasal cavity that responds to pheromones. Research echoes over and over again, that cinnamon bread baking in a home along with coffee smells can sell a home, but dog smells can stop a sale.
These systems of smell, emotion, and memory are shown to go through the orbito-frontal cortex, the medial orbito-cortex, into the thalamus down into the nucleus of the solitary tract and down the brain stem. The taste system is also connected to the Olfactory system and all associated pathways of memory, emotion, smell and taste patterned pathways. I love lobster, and it is related to smell, to taste, to patterned memories and makes my stomach tighten with excitement when I think of eating lobster and this just on a patterned memory. However, the smell of the stress molecules also sets off a patterned memory of negativity, and it triggers a strong response now on every 19th of every month as my husband’s does, from his PTSD. The brain is an absolutely marvelous operating machine for adaptation so we as humans can survive.
This research of two biological organisms, is done by Carolyn d Hogarth and shared for Scientific research and reinforcement of many studied subjects known. The amygdala and limbic systems attached to smell, taste, and our thalamus that travel into different areas of the brain and down the tract of the brain stem, a fascinating query done for many years. This day of March 22nd, 2023.
