The allure of psychoactive substances for many is the ability to slip into another realm of perception – a world dominated by exaggerated sensations. While psychedelic substances like LSD are known primarily for visual and auditory hallucinations, cannabis can also provoke similar effects on sensation and perception. But one particular sensory effect – known as synesthesia, or the mixing of the senses – can occur independently without the help of external substances.
Synesthesia is a fascinating and rare experience that has perplexed and delighted physiologists since it was first discovered.1John Locke is credited with recording the first written account in 1690.2 Many years later, in 1883, Francis Galton described this peculiarity of the senses in greater detail. So, what exactly is synesthesia?
In rare events, a stimulus (such as an image or sound) will evoke the perception of another sense; for example, “tasting” a word or “seeing” a touch. Many different types of synesthesia have been reported but the prevalence of the mixing of the senses is quite low, affecting approximately 4% of the population.2,3
Since relatively few people experience this strange effect, it’s easy to think that perhaps they are embellishing a bit of the truth or that they may be experiencing these sensations as symptoms associated with another condition.There is scientific evidence, however, to prove this this experience is indeed hard-wired. Imaging studies have shown that regions of the brain associated with different sensations like hearing or seeing are activated differently in people with synesthesia. For example, visual areas of the brain light up in people who “see” sounds.2
While scientists aren’t exactly sure what causes synesthesia, it is likely that wires in the brain got crossed somehow during development. But, people whose brains are not mixed up can still experience synesthesia by taking certain substances.
While psychedelic substances are well known for their effects on mixing of the senses and exaggerated perception, there are a few reports of cannabis-induced synesthesia. In these cases, people reported experiencing auditory-visual synesthesia; it is also believed that these cases only occur at very high doses.4-7 These data are taken from surveys or anecdotes and therefore do not represent rigorous measures from clinical studies.
So, is cannabis-induced synesthesia fact or fiction? Case reports suggest that it is possible but, until we have consistent evidence from controlled studies, the fact of the matter is still up for debate.
References
- Banissy, M.J., Jonas, C.,Kadosh, R.C., “Synesthesia: An Introduction”, Front Psychol,2014, Volume 5, pg. 1-3.(impact factor: 2.321; cited by: 5)
- Mulvenna, C., Walsh, V.,“Synaesthesia”,Current Biology,2005, Volume 15, pg. R399-R400. (impact factor: 8.851; cited by: 24)
- Marks, L.E.,“On Colored-Hearing Synesthesia: Cross-Modal Translations of Sensory Dimensions”,Psychological Bulletin, 1975, Volume 82, pg. 303-331. (impact factor: 16.793; cited by: 486)
- Luke, D.P.,Terhune, D.B., “The Induction of Synaesthesia with Chemical Agents: A Systematic Review”,Front Psychol,2013, Volume 4, pg. 1-12. (impact factor: 2.321; cited by: 47)
- Tart, C., “Marijuana Intoxication: Common Experiences”,Nature, 1970, Volume 226, pg. 701-704.
(impact factor: 41.577; cited by: 265)
6. Marincolo, S., High. Insights on Marijuana, March 2010, Dog Ear Publishing. (impact factor: N/A; cited by: 7) - Sinke, C., Halpern, J.H., Zedler, M., Neufeld, J., Emrich, H.M., Passie, T.,“Genuine and Drug-induced Synesthesia: A Comparison”,Consciousness and Cognition, 2012, Volume 21, pg. 1419-1434. (impact factor: 2.272; cited by: 56)
