“No sooner had the warm liquid mixed with the crumbs touched my palate than a shudder ran through me, and I stopped, intent upon the extraordinary thing that was happening to me.”
Marcel Proust, In Search of Lost Time (1913)
Whether it is the scent of a vaporised cannabis flower or the complex aroma of freshly brewed hemp tea: what moves us in such moments, long before we consciously smell anything, is more than a chemical stimulation of sensory cells. It is the start of a fascinating neurobiological cascade that leads deep into the oldest regions of our brain. This cascade changes not only our perception but also influences memories, emotions and possibly physiological processes throughout the body.
Proust: chasing lost time with psychoactive substances
Marcel Proust's monumental novel cycle In Search of Lost Time (1913–1927) is perhaps the most famous literary monument to the power of sensory memory. At heart, the whole work is a hunt: the systematic recovery of forgotten moments of life through the force of involuntary memories, triggered by tastes, smells and touch.
In January 1909 Proust had the key experience that would become the nucleus of his life's work: a rusk dipped in tea, stylised in the novel as the famous madeleine, carried him back to his childhood without any effort of will (1). From this single experience he developed his theory of two forms of memory: conscious, voluntary recollection and spontaneous, involuntary memory (mémoire involontaire).
Less well known is that Proust was no inexperienced wanderer in what the British historian Richard Davenport-Hines, in Proust at the Majestic (2), called the “wondrous jungles of the unconscious”. Throughout his life Proust used an astonishing range of psychoactive substances, including caffeine, opiates, barbiturates, amyl nitrite and adrenaline, and very probably cannabis as well. Writing in the New York Review of Books in 2006, Graham Robb noted that the variety of substances that went into the making of La Recherche was “probably unequalled in French literature” (3). For Davenport-Hines, Proust's habitual drug use was not least a way “to feed his explorations of the exciting, wondrous jungles of the unconscious”.
Proust's literary role model was a poet who certainly knew cannabis well from his own experience: Charles Baudelaire. In his literary essays Contre Sainte-Beuve (written 1908–1909, published posthumously in 1954) Proust pays extensive tribute to Baudelaire and calls him “the greatest poet of the 19th century” (4). Baudelaire in turn was one of the central figures of the Club des Hashischins, which met regularly from 1844 to 1849 at the Hôtel Pimodan on the Île Saint-Louis in Paris. Founded by the psychiatrist Jacques-Joseph Moreau de Tours as a scientific experiment, the circle brought together France's literary elite: Théophile Gautier, Alexandre Dumas, Victor Hugo, Gérard de Nerval, Honoré de Balzac, Eugène Delacroix. In 1845 Moreau published Du hachisch et de l'aliénation mentale, the world's first scientific monograph on a psychoactive substance (5). Baudelaire himself recorded his experiences in Les Paradis Artificiels (6), a work Proust demonstrably knew and admired.
Cannabis is mentioned explicitly in Proust's masterpiece. In the third volume, Le Côté de Guermantes (The Guermantes Way), Proust describes the “secret garden in which grow like unknown flowers the so different kinds of sleep, the sleep induced by datura, by Indian hemp, by the multiple extracts of ether (the sleep of belladonna, of opium, of valerian), flowers whose petals remain closed until the day when the predestined stranger comes to open them with a touch and to release for long hours the aroma of their peculiar dreams” (7).
Proust's work is therefore not only the literary showpiece on the memory-evoking power of scent. It also stands in a Parisian tradition that explored the relationship between consciousness, memory and the effects of plants more systematically than almost any other era.
The olfactory brain: a direct line to the limbic system
On an area of only about five square centimetres of olfactory mucosa in the upper part of the nasal cavity, humans have some 20 to 30 million olfactory cells. They carry around 400 different types of olfactory receptors, encoded by the largest contiguous gene family in the human genome (8). Linda Buck and Richard Axel received the 2004 Nobel Prize in Physiology or Medicine for this fundamental discovery. According to estimates, humans can distinguish more than one trillion different odour mixtures (9).
What makes the sense of smell anatomically unique is its direct access to the brain. While all other sensory impressions (sight, hearing, touch, taste) are first relayed through the thalamus before we become aware of them, olfactory signals take a privileged, direct route: via the olfactory bulb they reach the amygdala, the emotional centre of the brain, and the hippocampus, the central memory structure (10). In neurobiological terms, this is exactly why a scent can take us back to a long-forgotten time within a split second.
The “Proust phenomenon”: why scents trigger such strong memories
Systematic research confirms what Proust described intuitively. Memories triggered by scents differ clearly from those evoked by visual or auditory cues. They are older, more emotional, more vivid and rarer. Researchers sum up these properties in the acronym LOVER: Limbic, Old, Vivid, Emotional, Rare (11). fMRI studies showed that odour-evoked autobiographical memories activate the amygdala and the hippocampal region significantly more strongly than comparable visual cues (10). A later case study impressively documented that direct electrical stimulation of the amygdala can trigger the Proust phenomenon immediately (12).
An early review already confirmed that olfactory-evoked memories are not only older but also noticeably more emotional than memories from other sensory channels (13). More recent studies add to these findings: odour-evoked experiences of nostalgia can have measurable effects on the immune system and interact with the release of certain cytokines (14). So the sense of smell is not a passive chemical detector but a biological time traveller with effects on the whole body.
Cannabis and episodic memory: an old observation, a new hypothesis
In many of my books, such as What Hashish Did to Walter Benjamin (15), The Art of the High (16) and Elevated. Cannabis as a Tool for Mind Enhancement (17), I describe a phenomenon that many cannabis users have reported for centuries, Proust and the writers of his time included: during a well-dosed high, episodic memory, that is, memory for the episodes of our own life, seems not weakened but intensified. Users report more detailed memories of long-past episodes, more vivid inner images and emotionally more intense moments of reliving.
In my work I have put forward the hypothesis that such reports describe an improved ability to remember that arises from a complex interplay of other effects of cannabis on our consciousness. Many users, for example, describe a hyperfocusing of attention and a heightened power of imagination during a cannabis high. Taken together, these effects could help us to put ourselves back into our earlier selves more easily during a high and to relive early memories of events. Hyperfocusing on our memories could then allow us to notice more details in them.
So far, however, a fascinating follow-up question remains unanswered: could the aromatic components of cannabis and hemp, the terpenes, esters and volatile sulphur compounds I wrote about in the article on the aroma of cannabis, make their own contribution to the intensity, sharpness of detail and recall of memories?
Neurobiologically the hypothesis is plausible: the direct connection of the olfactory pathways to the hippocampus and amygdala means that every draw on a vaporiser, every sip of hemp tea and every opening of a pack of flowers sends olfactory signals straight into the very brain regions responsible for consolidating and recalling emotional memories. Whether and how strongly this effect actually contributes to the described intensification of memory during a high has not yet been studied systematically. But the “aromatic time travel” is a hypothesis that deserves further research.
Hanns Hatt: olfactory receptors are not only found in the nose
We owe one of the most astonishing discoveries of the last two decades to the German cell physiologist Hanns Hatt of Ruhr University Bochum. From the early 2000s onwards, Hatt showed in dozens of papers that olfactory receptors are by no means limited to the nasal mucosa. They are found in the skin, in hair, in the gut, in the prostate, in the kidneys, in the heart, in sperm and even in the brain (18, 19). These “ectopic” or “extranasal” olfactory receptors do not produce conscious smells. They do, however, work as precise chemical detectors that respond to specific odour molecules and then set cellular signalling cascades in motion.
Hatt's research group showed, for instance, that a synthetic sandalwood odorant triggers processes involved in wound healing in skin cells via the olfactory receptor OR2AT4 (19). Other groups found olfactory receptors in intestinal cells, where they are involved in regulating peristalsis. Functionally active olfactory receptors have also been identified in the lungs, in the vascular system and even in tumour cells (20).
Possible pharmacological pathways of cannabis aromas
What does this mean for cannabis and hemp? The aromatic compounds, that is terpenes such as myrcene, limonene, linalool and β-caryophyllene, but also esters, volatile sulphur compounds and flavonoids, enter the bloodstream during vaporising, brewing or oral intake not only through the nose but also through the lungs and the digestive system. There they could, in theory, reach and activate extranasal olfactory receptors throughout the body.
For some cannabis terpenes, direct molecular effects have already been demonstrated, although not primarily via olfactory receptors: β-caryophyllene binds to CB2 receptors of the endocannabinoid system (21), linalool interacts with GABA receptors, and a recent study from the University of Arizona showed that several cannabis terpenes act in a cannabimimetic way via CB1 receptors (22). A clinical study in humans looked at whether vaporised d-limonene can reduce the acute anxiety-inducing effect of THC and found indications that it may (23). How much of this runs through classic receptor pathways and how much possibly also through the widely branched system of extranasal olfactory receptors is an open research question. Based on current knowledge, no clinically confirmed conclusions can be drawn from it.
Outlook: a fascinating research journey
For a long time, science and medicine dismissed and neglected the sense of smell as the “poor relation” among the senses. Only in recent decades have we begun to understand what a fascinating system lies behind it, as Hanns Hatt and his colleagues show: a chemosensory network spanning the entire body that modulates our emotions and is involved in many other mental and physiological functions.
Cannabis is one of the most aromatically complex plants of all. We now know that it acts, among other things, on the human endocannabinoid system, the fine regulatory system that controls a wide range of functions in body and mind. Beyond that, the complex aroma of cannabis could hold even greater potential that research is only beginning to explore, for example with regard to changes in consciousness such as the ability to recall memories more intensely and in greater detail.
A fascinating research journey lies ahead of us. It is time we set off.
Scientific sources
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