Carl Sagan, Cannabis, and The Right Brain Hemisphere

„What it comes down to is that modern society discriminates against the right hemisphere.“

Roger Wolcott Sperry (1913-1994), neuropsychologist and neurobiologist, known for his revolutionary studies of split brain patients


In 1971, Harvard Prof. Lester Grinspoon published his milestone book „Marijuana Reconsidered“, in which he featured an essay “Mr. X” by his best friend, the famous astronomer and science popularizer Carl Sagan. [1] In his essay, Sagan reports that for him, the marijuana high led to various cognitive enhancements, including the enhancement of cognitive abilities like enhanced episodic memory, pattern recognition, creativity, and the ability to produce insights. More than forty years later, Sagan’s essay “Mr. X” is still one of the most illuminating accounts on the positive mind-altering potential of the marijuana high. Many other cannabis users before and after Sagan have described similar mind enhancements during a high. My own experiences with the marijuana high had been very similar, and my research aims to explain how good quality marijuana can induce insights and many other cognitive enhancements, given that it is used by skilled users.[2]

Sagan’s Hypothesis

Sagan was so excited about the cognitive enhancements he experienced with marijuana that he used it on a regular basis to come to insights for his work. His biographer Keay Davidson wrote that when Lester Grinspoon received unusual high-quality marijuana from an admirer by mail, he shared the joints with his friend Sagan and his wife Ann Druyan. “Afterward, Sagan said, ‘Lester, I know you have only got one left, but could I have it? I’ve got serious work to do tomorrow and I could really use it.”[3]

Sagan was famous – or, for many of his academic colleagues, infamous – for making brilliant but daring speculations – not only in his field of astronomy, but also in other scientific fields. As his biographer Davidson remarks, Sagan for instance wrongly predicted the existence of complex organic molecules on the moon; but, Davidson adds, “(a)s it turned out later, complex organic molecules pervade much of the outer solar system and beyond.”[4]

In his Pulitzer price-winning book “The Dragons of Eden – Speculations on the Evolution of Human Intelligence”(1977), Sagan summarized what cognitive and evolutionary scientists had to say about the evolution of the human mind and presented many of his own brilliant speculative ideas on the nature and evolution of human intelligence. He also introduced a speculative thesis about the effects of marijuana on the human brain. Sagan started from an analogy made by psychologist Robert Ornstein:

“He {Ornstein} suggests that our awareness of right hemisphere function is a little like our ability to see stars in the daytime. The sun is so bright that the stars are invisible, despite the fact that they are just as present as they are in the daytime as at night. When the sun sets, we are able to perceive the stars. In the same way, the brilliance of our most recent evolutionary accretion, the verbal abilities of the left hemisphere, obscures our awareness of the functions of the intuitive right hemisphere, which in our ancestor must have been the principal means of perceiving the world.”[5]

In a now famous footnote to this paragraph Sagan formulates his hypothesis on how a marijuana high could affect thinking:

“Marijuana is often described as improving our appreciation of and abilities in music, dance, art, pattern and sign recognition and our sensitivity to nonverbal communication. To the best of my knowledge, it is never reported as improving our ability to read and comprehend Ludwig Wittgenstein or Immanuel Kant; to calculate the stresses of bridges; or to compute Laplace transformation. (…) I wonder if, rather than enhancing anything, the cannabinols (the active ingredient in marijuana) simply suppress the left hemisphere and permit the stars to come out. This may also be the objective of the meditative states of many Oriental regions.”[6]


Enhancements and Suppression

Let me distinguish two aspects of Sagan’s hypothesis: First, there is his observation that a marijuana high leads to a style of thinking which cognitive scientists consider to be predominantly based in the right hemisphere. Second, Sagan speculates that a marijuana high might suppress left hemisphere functions and, therefore, leads to what we could call “right hemisphere thinking”. Sagan’s hypothesis was based on his knowledge of what current science had to say about the human brain and the different style of cognition in the left and right brain hemispheres, as well as on his own experiences with marijuana.


Sagan’s Claim Reconsidered

During his lifetime, Sagan did not reveal to the public that he was a user of marijuana. In isolation, Sagan’s footnote about marijuana and its possible effect on the brain hemispheres may seem to be a spontaneous speculation out of nowhere. Yet, when reading Sagan’s essay “Mr. X”, it becomes clear that Sagan’s experiential basis for such a claim was actually quite broad. In his essay, he describes in some detail not only the enhancements outlined in his footnote, but he also mentions other cognitive enhancements, such an enhanced ability to remember past events and to obtain deep insights. Also, Sagan mentions that during a high, he also experienced enhanced

”perceptions of real people, a vastly enhanced sensitivity to facial expressions, intonations, and a choice of words which sometimes yields a rapport so close it’s as if two people are reading each other’s minds.”[7]

Sagan already knew that most of the cognitive enhancements he had experienced during a high concern functions which cognitive science at the time found to be predominantly located in the right brain hemisphere; he had described the research concerning split brain patients and more on the pages preceding his hypothesis in “The Dragons of Eden”.

Lester Grinspoon

So, Sagan knew this research and had made his own experiences with cognitive enhancements during a marijuana high. Furthermore, he was also well acquainted with his friend Lester Grinspoon’s research about marijuana as a medicine and about the mind-enhancing potential of marijuana. As Lester Grinspoon told me in private conversation, Carl Sagan had carefully read and commented upon his manuscript of “Marijuana Reconsidered”, in which Grinspoon extensively featured reports of other marijuana or hashish users who had described similar mind enhancements.

To summarize, then, Sagan’s hypothesis certainly didn’t come out of nowhere. Quite on the contrary, his knowledge about the differences in right and left hemisphere cognition style was quite impressive, and he knew a lot about the altered style of cognition during a high from his own experiences and from countless user’s reports he knew from Grinspoon’s work.

Now, what can we say about Sagan’s hypothesis almost 40 years later, with all the progress in the mind sciences on the nature of cognition in the respective brain hemispheres and with our knowledge about the endocannabinoid system and its many functions in cognition? Was Sagan on the right track?

Tragically, Sagan died in 1996, too early to witness the revolutionary discovery of the endocannabinoid system which started around that time. Since then, we have learned about the amazing range of its physiological and cognitive functions. So, can we actually find evidence for or against Sagan’s hypothesis for instance looking at the distribution of endocannabinoid recepors (especially the CB-1 receptor, on which the exogenous THC acts)?


Sagan’s Thesis and the Endocannabinoid System

As far as I can see, there does not seem to be extensive research concerning the subject of lateralization and the role of endocannabinoid signaling for higher cognitive functions. One often cited study found an increased blood flow in parts of the right hemisphere during a high[8], but another study states that relatively high concentrations of cannabinoid receptors were consistently seen in cortical regions of the left (dominant) hemisphere, known to be associated with verbal language functions.“[9]

It seems much too early to draw conclusions from brain imaging studies to evaluate Sagan’s hypothesis. Even better data on the concentrations of endocannabinoid receptors in the respective brain hemispheres will not directly lead to resolving the issue; Marsicano and Kuhner remind us that „sometimes the endocannabinoid system appears to be functionally important in regions or cell types where the density of CB1 receptor is relatively low {e.g. control of pain perceptions in the brainstem}.”[10] As far as I can see, we haven’t yet begun to understand how the endocannbinoids are involved in affecting different higher cognitive functions based in the left or right brain hemisphere.


Recent Neuroscience and Reports about the Marijuana High

Some more support for Sagan’s thesis seems to come from two other sources. First, Sagan’s description of the cognitive enhancements during a marijuana high have been described in detail by many more cannabis users.[11] The most impressive collection of recent anecdotal reports and essays about those enhancements comes from Sagan’s best friend Lester Grinspoon and can be found on his website Many of the enhancements reported by marijuana users seem to be based on a shift towards a more right-hemisphere cognition style during a high.

Second, if we look at what recent neuroscience has to say about differences in the cognitive functions and processing styles in the two brain hemispheres, Sagan still seems to have a point. From what we know now, the right hemisphere plays an important role for the cognitive processes named by Carl Sagan as enhanced during a high, as well as for many other enhancements described by other marijuana users. In his book The Master and his Emissary. The Divided Brain and the Making of the Modern World, (2009), psychiatrist Ian McGilchrist gives a survey of the current scientific knowledge about the different styles of cognition in the left and the right brain hemisphere emerging from stroke cases in one hemisphere, split brain patient cases, and newer brain imaging studies. According to McGilchrist, the right hemisphere is predominately involved in our ability to remember personal events (episodic memory), is responsible for associations between widely different concepts and ideas, complex pattern recognition, creative problem solving, insights, the appreciation of humor, the understanding of metaphors, self-awareness, the empathic understanding of others, the processing of words describing the mind, and the interpretation of emotional expression in faces, in intonation and verbal implications. Also, the right hemisphere seems to be crucially involved in the interpretation of non-verbal communication and the perception of music. For the sake of brevity, I will leave it at this incomplete list, but actually, McGilchrist describes more cognitive functions as right hemisphere based, functions which all have been consistently reported by countless users to be enhanced during a high.


The Effects of Marijuana on Attention

In general, then, it seems that research of the last forty years in the neurosciences lend some more support Sagan’s thesis that marijuana leads to an enhancement of right hemisphere-based cognitive abilities. One interesting puzzle, though, is one of the fundamental effects of marijuana on attention. During a marijuana high, we seem to ‘hyperfocus’. High users often get completely absorbed by the taste of ice-cream, by an intense stream of memories or ideas, or by the sensation of a kiss.

In other words, a high seems to cause a strong selective focus on whatever we attend to. According to McGilchrist, however, focussed attention is not a cognitive function performed primarily in the right hemisphere. Quite on the contrary, he summarizes the current research as saying that “(…) the right hemisphere is responsible for every type of attention except focused attention.”[12]


Evaluating Sagan’s Hypothesis

So, when it comes to attention, at least one of the typical cognitive changes during a high does not seem to come from an enhancement of processes in the right hemisphere. Generally, then, while Sagan seems to have been basically on the right track with his hypothesis, not all of the cognitive enhanced functions during a high seem to be predominately based in right hemisphere activities. We will have to wait for more research to be done in this field to see how exactly cannabis affects cognitive activities in the left and right brain hemisphere.

What about Sagan’s hypothesis that a high could suppress left hemisphere function and, thus, ‘bring out the stars’ and allow for an enhanced right hemisphere activity? As far as I can see, we are far from being able to tell whether the mind enhancements during a high observed by so many users come from a direct enhancement of certain cognitive functions, or whether they arise from a suppression of some left hemisphere activities.

According to McGilchrist, the left and the right hemisphere are in a constant battle for control. In order to help us to survive, we and other animals need two conflicting systems of attention. He explains this point with the example of birds: to pick up seeds for food, a bird needs to narrowly focus on the seeds on the ground to motor control and coordinate food intake (left hemisphere function); but in order to survive, the bird has to get distracted by a predator like a fox or a falcon in the fringe of its perception. So there must be another type of attention drawing it to unusual new sensations (right hemisphere). Only the interplay of these competing attention systems located in the two brain hemispheres allows birds and other animals like us to survive. Clearly, then, an enhancement of cognitive processes in one hemisphere could come from the suppression or weakening of cognitive functions in the other hemisphere.

We still have to await further research to come to a better understanding on how consumed cannabinoids affect the endocannabinoid system and, generally, its role in higher cognition. Yet, almost forty years after Sagan’s hypothesis, I think we can still say that he was on an interesting track. As far as I can see, we will only come to a better understanding of the nature of the high and its effects on attention, memory, pattern recognition, creativity, empathy, or insights, once we are beginning to research how endocannabinoids and consumed marijuana affects various cognitive processes in the left and the right brain hemisphere.


A Historical-Sociological Perspective

Sagan’s hypothesis does not only have interesting implications for individual marijuana users. In his book The Master and his Emissary. The Divided Brain and the Making of the Modern World, Ian McGilchrist argues in detail that in various periods of history there were general shifts in our (Western) society toward more left or right hemisphere cognition styles which can be detected in art, science, philosophy, literature and politics:

“My thesis is that for us as human beings there are two fundamentally opposed realities, two different modes of experience; that each is of ultimate importance in bringing about the recognizably human world; and that their difference is rooted in the bihemispheric structure of the brain. It follows that the hemispheres need to co-operate, but I believe that they are in fact involved in a sort of power struggle, and that this explains many aspects of contemporary Western culture.[13] (…) I believe that over time (…) the balance of power has shifted where it cannot afford to go – further and further towards the part-world created by the left hemisphere.”[14]

For McGilchrist, this means that in our society we now predominatently rely on left hemispheric thinking; which leans towards abstraction, is more rational, mechanistic, less empathic, less open to the richfulness of holistic experience, and “yields clarity and power to manipulate things that are known, fixed, static, isolated, decontextualized, explicit, disembodied, general in nature, but ultimately lifeless.”[15]

The right hemisphere, by contrast, represents the world to us as “individual, changing, evolving, interconnected, implicit, incarnate, living beings within the context of the lived world, but in the nature of things never fully graspable, always imperfectly known – and to this world it exists in a relationship of care.”[16]

Just like Sagan, McGilchrist does not simply speak in favor of right hemisphere thinking, but reminds us that sane human cognition comes out of a balanced interplay between the two hemispheres. If McGilchrist is right, then what we dramatically need in our society is to come back from our imbalanced left-hemispheric thinking by using mindfulness or other techniques like meditation.[17] If Sagan is right with his general hypothesis that a marijuana high actually does cause a more right-hemisperic style of thinking, then it is easy to see how skilled and knowledgeable marijuana use in our society could lead to positive changes in the mindset and thinking of our society as a whole. If we look back in recent history, we have already seen these changes happening and leading to vastly important positive cultural changes, from the early evolution of jazz to the peace movement of the beat generation. From this perspective, more widespread marijuana use might as well play an defining role in the elementary changes in our society yet to come; changes which could possibly help to save the world we live in.


[1] Carl Sagan, „Mr. X“, in: Lester Grinspoon (1971), „Marijuana Reconsidered“, Harvard University Press, Cambridge, Massachussetts, p. 123 – 130. Sagan’s essay was published anonymously, Grinspoon revealed the identity of his author only years after Sagan’s untimely death.

[2] See Sebastian Marincolo (2010), „High. Insights on Marijuana“, Dogear Publishing Indianapolis, Indiana.

[3] Keay Davidson, (1999), „Carl Sagan. A Life.“, John Wiley & Sons, Inc., New York, p. 214.

[4] Ibid., p. 213.

[5] Carl Sagan (1977) „The Dragons of Eden. Speculations on the Evolution of Human Intelligence“, Random House Publishing Group, New York, p. 177

[6] Ibid.

[7] Carl Sagan, „Mr. X“, in: Lester Grinspoon (1971), „Marijuana Reconsidered“, Harvard University Press, Cambridge, Massachussetts, p. 127.

[8] Roy Mathew et al. (1997) , „Marijuana intoxication and brain activation in marijuana smokers“, Life Sci. 1997;60(23):2075-89.

[9] Glass, M., Dragunov, M., Faull, RL (1997) „Cannabinoid receptors in the human brain: a detailed anatomical and quantitative autoradiographic study in the fetal, neonatal and adult human brain.“ Neuroscience. 1997 Mar; 77(2): p. 299-318.

[10] Marsicano, G., and Kuner, R. (2008), „Distribution of CB1 Cannabinoid Receptors in the Nervous System“, in: Attila Köfalfi (ed.) (2008), „Cannabinoids and the Brain“, Springer Science and Business Media, New York, p. 164.

[11] Compare Sebastián Marincolo (2010), „High. Insights on Marijuana“, Dogear Publishing Indianapolis, Indiana.

[12] McGilchrist, Ian (2009), „The Master and His Emissary, The Divided Brain and the Making of the Modern World“, Yale University Press, New Haven and London, p. 39.

[13] Ibid, p. 3.

[14] Ibid, p. 6.

[15] Ibid, p. 174.

[16] Ibid, p. 174.

[17] Margaret Emory (2012) „Dr. Ian McGilchrist on the Divided Brain, Q&A with Ian McGilchrist“, BrainWorld, May, 8 2012,


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