One of the most characteristic features of odor memory in humans is the rather unique ability of odors to vividly trigger the evocation of emotional experiences. This property might be sustained by the direct connections established by the olfactory bulb and piriform/olfactory cortex on two structures involved in emotion and memory, namely the amygdala and hippocampus.
I've started from this basic assumption that odors are able to eliciting memories, to vividly trigger some emotions from the past, in such a way that most of the times we don't even realize. There is more than just molecules in odors, there are feelings, expectations, people. How unconfortable can be to deal with unpleasant in public? You can't avoid bad smells unless you stop breathing. Smelling it's a complex experience, mainly uncounscious, it can take you back in time when you were a kid or can lift you up when you smell the one that you love.
Then I started to think about the olfactory sense in newborn babies. So in a phase of your life where you can't see anything, hear anything and you can't speak the only way to interact with the external world is the olfactory sense. There is a scent made of molecules that guide the baby to the mother's breast, leading to the mother-infant attachment process. A sort of primodial connection that starts already inside the mother body, apparently babies start to smell in the intrauterine life the amniotic fluid. Smelling the amniotic fluid in the firsts moments after the delivery facilitate the baby to accept the mother nipple.
From these considerations I started eleborating this canvas, combining simbolic images of The Mother as a female powerful human being that gives life and take cares of it and neuroanatomy drawings to create a stream of lines, words and molecules.
Neuroanatomy of the Olfactory Pathways
Olfactory sensory neurons lie in the olfactory epithelium, which covers the back of the nasal cavity. The axons of the olfactory sensory neurons travel through the cribriform plate to the olfactory bulb, which is the first relay of olfactory information. The olfactory bulb output neurons send direct projections to the olfactory cortex, including the anterior olfactory nucleus, the olfactory tubercle, and the piriform or olfactory cortex. The first unusual characteristic of the mammalian olfactory pathways is that, unlike other sensory systems, it does not need to pass through the thalamus to reach cortical areas. Indeed, there is no thalamic relay between the first relay of sensory information, namely the olfactory bulb, and the primary olfactory cortex, as is the case for other sensory modalities. Similarly, there is no obligatory thalamic relay for olfactory information to reach the orbitofrontal cortex. Indeed, although the piriform cortex sends sparse projections to the mediodorsal thalamus, thereby disynaptically targeting the orbitofrontal cortex, it establishes direct monosynaptic connections with the orbitofrontal cortex. These observations suggest that the thalamus might be less relevant for olfaction than for the other senses.
Another unique feature of the olfactory pathways is the olfactory bulb’s output neurons rapid connections to structures crucially implicated in emotion and memory, namely the amygdala and the hippocampus. Indeed, the main olfactory bulb makes dense monosynaptic contacts with nuclei of the corticomedial amygdaloid group, including the nucleus of the lateral olfactory tract, the cortical nucleus of the amygdala, and the periamygdaloid cortex. These observations led to suggest that the corticomedial amygdala is an integral component of the olfactory system. These superficial nuclei are a major source of the projections from the amygdala to the hypothalamus. In contrast, the deeper amygdaloid nuclei, including the basolateral nuclear group, do not receive projections from the olfactory bulb and receive relatively weak projections from the olfactory piriform cortex. However, they receive fairly dense projections from the corticomedial nuclei within the amygdala. Taken together, these anatomical data suggest that compared to the other sensory modalities, olfactory information has a unique direct access to the amygdala.
The limbic system
In mammals, perception of smells during the first hours of life is an essential prerequisite for adaptation of the newborn to the new extrauterine world. Naturally occurring odours play an important role in the mediation of the infant's behaviour. Even fetal olfactory learning seems to occur and breast odours from the mother exert a pheromone-like effect at the newborn's first attempt to locate the nipple. Newborns are generally responsive to breast odours produced by lactating women. Olfactory recognition may be implicated in the early stages of the mother-infant attachment process, when the newborns learn to recognize the own mother's unique odour signature--a process possibly facilitated by the high norepinephrine release and the arousal of the locus coeruleus at birth. Additionally newborn young of several mammalian species are attracted to the odor of amniotic fluid (AF); these chemical cues also appear to calm neonates and help them adapt to their novel postnatal environment. AF odor likewise elicits positive (head orientation) responses by human infants. Hypothesis suggest that the fetus may become familiar with chemical cues present in the intrauterine environment. Our data provide new evidence of the human baby's fine olfactory discrimination capacity, and add to the growing body of evidence indicating that naturally occurring odors play an important role in the mediation of infants' early behavior.
Swann’s Way, by Proust (1919)
“The memory suddenly appears before my mind. The taste was that of the little piece of madeleine which on Sunday mornings at Combray (because on those mornings I did not go out before church-time) my aunt Leonie used to give to me, dipping it first in her own cup of real or lime-flower tea’, leading him to the conclusion that ’When from a long-distant past nothing subsists … the smell and taste of things remain poised for a long time … and bear unfaltering, in the tiny and almost impalpable drop of their essence, the vast structure of recollection.”
Sources:
https://www.ncbi.nlm.nih.gov/books/NBK55967/
Winberg J, Porter RH. Olfaction and human neonatal behaviour: clinical implications. Acta Paediatr. 1998; 87(1):6-10.
Winberg J. Mother and newborn baby: mutual regulation of physiology and behavior--a selective review. Dev Psychobiol. 2005; 47(3):217-29.
Bartocci M et al. Activation of olfactory cortex in newborn infants after odor stimulation: a functional near-infrared spectroscopy study. Pediatr Res. 2000; 48(1):18-23.
Varendi H. et al. Soothing effect of amniotic fluid smell in newborn infants. Early Hum Dev. 1998; 51(1):47-55.
