How your brain imprints those chemical cannabis memories
You can sense its presence without seeing a thing. Upon entering a room, that pungent cannabis odor sits deep within the space, inviting you in. Imbibing cannabis is truly a multisensory experience that involves just about every specialized cell in your body. But your nose is the first to let you know that it’s not basil or oregano lingering in that drawer.
Humans are species-centered, often forgetting that other animals use their senses in very different ways. For us, it’s the eyes that drink up the world, with taste, smell, touch, and hearing amplifying the sight before us. But, for most other creatures, including our domestic furry friends, it’s the smells that lead the way. And so, the olfactory system elegantly parses out a myriad of chemicals taken in during each breath to identify and recall what each odor is and what it means to us.
In the very front of the brain (above your eyes) sit the olfactory bulbs. While they hang off the cortex rather indelicately, their structure and what lies within is truly remarkable. Olfactory sensory neurons express one specific type of odorant receptor, and each type may be more broadly or finely tuned to a range of odorants. These sensory neurons converge onto two glomeruli in the olfactory bulbs, which reflect a specific pattern of activity that allows for odor recognition and discrimination. 
In 2004, Linda Buck and Richard Axel received the Nobel Prize for their discovery that odorants bind to GTP-binding protein-coupled receptors, or GPCRs, that activate (you guessed it) G proteins (GTP = guanosine-5′-triphosphate). This activation kick-starts a chemical cascade in the cell.  Thus, odors inscribe a chemical code onto neurons that is interpreted and stored by the brain to bring you the full rich perception of the smell of a rose, or, even better, cannabis.
Olfactory perception is elegant and yet mysterious, as there is much to learn about how the complexities of this system work. We do know, however, that compounds with similar molecular structures are perceived to have similar odors. For example, esters have a floral scent, while aldehydes impart an odor likened to cut grass. Yet, these are odors in isolation, not part of complex compounds. Even further, enantiomeric compounds—which are structural mirrors of each other—are not similar in odor at all. 
There is tremendous diversity in the terpenes that exist in cannabis and many other plants. And the complex fragrance that each cannabis cultivar or product imparts is a direct result of the types of terpenes in those buds and the ratio of each terpene to each other.  But at each inhale, those specific terpenes imprint into your olfactory sensory neurons the exact molecular structure of their compounds, mingled into the overall sensation and whole-body feel of that cannabis experience.
In “Remembrance of Things Past,” Marcel Proust wrote of an early memory in which his mother gave him a madeleine that brought him great joy. Years later, just the taste and smell of that cookie unleashed a complex array of sensations bringing past sights, sounds, and youth to present. And we’ve all had such similar experiences.
A waft of perfume, a whiff of chimney smoke, a taste of something you hadn’t eaten in decades—and a flood of memories descends upon you at once. The olfactory and memory centers of the brain are strongly connected and while some of their conversations remain a bit mysterious, it is a powerful link that will always leave you unexpectedly pulled back into a previous moment in time.
So while our eyes get most of the credit for bringing beauty into our individual worlds, remember that it is our nose that knows exactly which terpenes we drink up. And the mark that they place on our olfactory neurons will reactivate as we bring up a terpinated bud and recall again a great cannabis experience—that summer, two years ago, the beach, the blue blanket—and that next memory you’ll make in time.[Image Source]
- Uchida., N, et al. “Coding and Transformations in the Olfactory System.” Annu Rev Neurosci. vol.37, 2014, pg. 363-385. (impact factor: 12.043; cited by: 48)
- Genva, M., et al., “Is It Possible to Predict the Odor of a Molecule on the Basis of its Structure?” Int J Mol Sci. vol.20, no.12, 2019, pg. 1-16. (impact factor: 4.183; cited by: N/A)
- Booth, J.K., Bohlmann, J. “Terpenes in Cannabis sativa – From Plant Genome to Humans.” Plant Sci. vol.284, 2019, pg. 67-72. (impact factor: 3.712; cited by: 6)