Sentience and Psychedelics

 The Promise of New Psychotherapy Catalysts

© Gérard Sunnen, MD

November 2024

Abstract

Links have been found connecting psychedelic phenomena to enhanced activity of selected brain neurotransmitter systems. Cortical activation of serotonin 5HT-2A receptor subtypes and its extensive ramifications produce far-ranging effects ranging from changes in the configuration of consciousness to neurogenesis. Understanding heightened neuronal network fluidity and cortical cross-connectonomic communication present exciting opportunities for integrating psychedelics in the treatment of a spectrum of clinical challenges to the human condition.

Introduction

The new era of clinical psychedelic research is kindling a surge of interest bordering on excitement. There’s even a nascent notion that major discoveries will be made leading to radically different ways of looking at self and humankind, maybe even piercing through one of the greatest questions facing the sciences today, namely the mind-body problem (Pollan, 2018; Alter, 2011), or how a seemingly immaterial medium, consciousness, can be linked to a biological entity, namely our nervous system network.

In the fifties and sixties, psychedelic usage was fueled by the promise of facile spiritual discovery. Inspired by Eastern concepts offering novel philosophies of life, psychedelics became popular as potential accelerators of personal evolution.

To illustrate the phenomena that commonly emerge during psychedelic exploration, I write on my first psychedelic experience which  took place in my late teens, using an established Native American recipe that called for three dried peyote cacti, while respecting a proper mind set, and a supportive loving milieu. If it was time-tested by native Americans, I thought, they had paved the way, and I felt safe. Not so, I would later say, for laboratory generated consciousness-altering molecules, where caution is much advised.

So I first rode this wave, as eventually did my parents who were meditation students of a spiritual man, Paramahansa Yogananda, author of Autobiography of a Yogi (Yogananda, 1946). I was  also inspired, as many were, by Aldous Huxley’s “Doors of Perception” (Huxley, 2009) and Alan Watts’ “Joyous Cosmology” (Watts, 2013).

After an hour or so, the arduous visceral effects of the magic cacti evaporated. Situated near a trio of pines in the slowdown of a Sunday and a soft breeze, all backdropped by a strikingly blue sky, I looked at the trees moving in the zephyr. Suddenly, I was jolted by a radically different perception. The trees, not only in their sway, but also in their every branch, even down to each needle, were now registered and understood, as in a lifting fog’s sudden clarity. Standing spellbound, I felt like I sensed nature’s powers coursing through the tree trunks, suddenly surprised by the intense wonderment of passing birds in flight, all as if seen for the very first time. Many energies seemed to fuse, including my own. In fact, the salient feature of the experience , as I retrieve it, is the intense perception of what I can only name as fluid energy. Which reality is correct, I asked myself, this “hyper-reality” as currently experienced, or the one so familiar?

My bodily demarcations fluidified, somehow feeling as if my body expanded in volume. More challenging, my experience of “Me” began to shift in unforeseen directions, a phenomenon known as “ego dissolution,” opening vistas into concepts on the malleability of the structure of self. Sensations melded in a moving mélange that would later be understood as synesthesia. At this juncture, I realized that I had a choice to make: Either I would let things happen as they would, with acceptance and relaxation; or, feeling that these challenges could portend darker outcomes, I would now backtrack by ending my experiment, however I could. This juncture, commonly encountered during psychedelic therapies, speaks for the beneficial presence of a guide who, aware of this possible conundrum, will bolster patients’ ego forces, while reminding them of their therapeutic objectives. They will then be more likely to come out of their journeys deriving strength and aplomb.

After several hours I welcomed returning to the familiar sense of “Me.” Yet, I remained deeply humbled by the realization that one’s so-familiar state of sentience could be so fundamentally transformed by ceremonial botanicals which, in mixing with brain dynamics, could so dramatically influence perception, cognition, mood, and the highest qualia of the experiencing self. I would later appreciate that these experiences embodied the hallmarks of commonly shared psychedelic peregrinations. Knowledge in working with these phenomena presages immense psychotherapeutic promise (Aixalà, 2022).

The first Western psychedelic surge and the new consciousness alchemy

As a first-year resident at New York’s Bellevue Psychiatric Hospital, the late sixties were a time for witnessing a new phenomenon. Half of our emergency unit adnmissions were brought by the police, and our acute unit, with its safety rooms for agitated patients, was rarely idle. Within a few months we saw our emergency population beginning to shift, as the classical DSM syndromes were now mixing with new and potent poly-pharmaceutical psychedelic brews. 

That era was one for free-for-all “mind-expanding” mystical molecular magic and its new psychedelic alchemy. Our patients, to our wonderment, would detail how they had mixed, smoked, brewed, distilled, imbibed and unfortunately injected, any permutation and combination of substances said to contain life-revealing properties. Blended with psilocybin in magic mushrooms, were mescaline, LSD, unknown compounds derived in rogue laboratories, morning glory seeds, hashish, ibogaine and then-mysterious plants from the Amazon and the Far East. In this age of experimentation, even psychiatric drugs, such as Thorazine and Elavil, easily obtained in street markets, found their way into creative concoctions. We regularly pondered, is this psychiatric emergency a case of acute schizophrenic decompensation, schizoaffective psychosis, bipolar mania, delirium, a neurological problem, an intoxication, a wild mix of the above, or simply a “bad trip?” 

The contemporary psychedelic wave 

This first Western massive psychedelic wave slowly subsided after some years. Decades later, however, a second wave arrived, here today, this one derived from the cumulated rich trove of discoveries into nervous system dynamics: Advances in brain imagery, neuronal circuitry mapping, psychosurgery and deep brain stimulation, neurotransmitter chemistry, all leading to a birthing appreciation for the secrets psychedelic research could unlock (Ballentine, 2022). 

If impaired circuitries are putative in the creation of psychiatric pathologies, could psychedelics, which appear to act at the very interface between brain chemistry and consciousness itself, be utilized to treat humankind’s psychic plagues, namely the spectrum of anxiety and trauma disorders, catastrophic depressions, thought pathologies, addictions and end-of-life existential tribulations? Today, hundreds of psychedelics are identified, its list ever-growing (Kelmendi, 2022). On a more fundamental level, could the psychedelic keys that appear to open portals to the kingdom of sentience gift us with insights about how a palpable organ, the brain, can generate a phenomenon called experiencing, revealing how so many varieties of emotions can emerge from a mere physical entity? (Penfield, 2015; Brazis, 2010; James, 1988). 

Connectonomics of consciousness

It has long been appreciated that the fullest expression of consciousness relies on the proper functioning of the cerebral cortex, in dynamic unison with subcortical arousal systems (Penfield, 1950; Plum and Posner, 1972). Neuronal circuitries creating alertness, awareness and attention, are referred to as the “consciousness system” (Blumenfeld, 2012).

Emerging from the brain stem are signals generated by billions of dense cells in net-like formations providing neural energies for descending, as well as ascending signaling. The ascending reticular activating system (ARAS) is a prime provider for the tonus of alertness – indeed, lesions there lead to coma (Kandel, 2021; Vincent, 2000; Laureys, 2016). Several distinct arousal networks travel to the highest cortical centers via the pons, mesencephalon, thalamus and hypothalamus, each mediated by specific neurotransmitters: Glutamate, acetylcholine, GABA, norepinephrine, dopamine, serotonin, histamine, orexin and adenosine, a growing number of lesser-known neuromolecules, and even neurotransmitter gases such as nitric oxide (NO) (Palasz, 2021; Vincent, 2000). From there, thalamo-cortical projections activate cortical connectomes to create the most delicate expressions of sentience (Gammel, 2023). 

The brain’s connectome is defined as the ensemble of all neurons that populate its universe (Stine, 2021). Its outbound nerves eventually immerse their finest tendrils far into the substance of every bodily organ, from skin, muscle and endocrine glands to immune networks, and back to the brain; as such, there are no clear boundaries to the brain’s connectome because it touches the intimate functions of all cells, determining the health of every organ. This principle forms the foundation for the practice of psychosomatic disciplines such as meditation and yoga, among others, that aim to harmonize all systems that contribute to our organism’s well-being. 

Numerous sub-connectomes inhabit the greater brain connectome (Bazinet, 2023). Sensory connectomes translate the constant messages of trillions of diverse bodily sensors into experiencing, while motor networks trace their circuitry from the elusive centers of volition, to muscle activation. Other connectomes, visual, auditory, memory and language share space with abstract ones, as those dedicated to thinking, creativity, and the most complex, selfhood. 

Although most connectomes function below the threshold of awareness, there is one connectome that is granted special status; it could be named the “Awareness Connectome.” While consciousness derives from the energetic contributions of the total neuronal population, awareness expresses the ignition of selected neuronal circuits that can quickly respond to the milieu’s immediate demands. It thus embodies essential adaptation and survival value. The normal serial shifting of mind’s attention reflects the scanning kinetics of this connectome. Fully able to center on incoming perceptions, it can also be dispatched omnidirectionally via the impetus of another connectome, one with elusive provenance, namely volition (Funahashi, 2008). This outgoing beam of awareness can delegate psyche into its soma, not only to expand its domain but also to influence internal bodily systems.

In Eastern perspectives, by contrast, awareness is interpreted as a form of transcendent energy. In the Tibetan Buddhist view, for example, the ultimate stuff of awareness belongs to a substance called the “subtle body” which can be conceived as belonging to a yet unidentified universal energetic dimension (Rinpoche, 1983).

The “Me Connectome”

Within the nebulae of neurons constantly pulsating with electro-chemical flux, resides an entity, known as a person. Is personhood a neurological entity or a spiritual presence? Our brain’s language centers give it a name: “Me,” manifesting as a poignant sense of experiencing oneself in an instant of time, namely qualia. Drawing on the contributions of limbic connectomes, it is imbued with poignant feelings such as self-esteem and self-worth. This “Me” connectome, as the central experiencer and executor of mental functions, has the challenging task of negotiating all signals entering and exiting consciousness. In classical parlance, this refers to a delicate balancing act between conscious id, ego and superego forces. Could psychedelic therapies, via their propensity to assuage the usual perimeters of self, move this connectome in the direction of greater self-acceptance and self-appreciation, so commonly expressed as personal goals for psychotherapy? 

Psychedelic neurotransmitter dynamics

Brain connectomes use numerous neurotransmitter molecules to activate, facilitate, modulate and inhibit their messages (Hansen, 2022). Cross-communication between all connectomes ensures that no one part of the nervous system is ever isolated from the others. Studies have consistently shown that activation of selected serotonin-based networks stimulates psychedelic actions on consciousness (Hatzipantelis, 2024; Doss 2023; Van Elk, 2022; Kwan, 2022). Fourteen serotonin receptor subtypes grouped in seven families have been identified (Vilaró, 2022). A consensus is reached that psychedelics’ core psychic effects are mediated via the engagement of 5HT-2A cortical receptors (Vargas, 2023; Ballentine, 2022; Carhart-Harris, 2017). These authors posit that cortical serotonin circuits are of two types. 5HT1A receptors are involved in stress modulation. Their activation - by SSRI antidepressants, for example - leads to nervous system appeasement and relaxation. 5HT2A cortical receptor activation, on the other hand, leads to the altered configuration of sentience observed in psychedelic action. How can the activation of extensive ramifications of this connectome be putative in the production of such profound alterations in the expression of qualia?

Sculpting sentient connectomes with meditative therapies, the possibility of “awareness neurons,” enhanced neuroplasticity and neurogenesis

What happens to brain’s circuitry when meditation is consistently practiced? Considering discoveries showing the capacity of meditation-induced neuronal generation (Gage, 2013; Hölzel 2011; Xue, 2011; Duan, 2008), is it possible to stimulate brain awareness networks to expand their demographics? Research shows that meditation, which essentially involves the practice of directing awareness onto itself, can alter the morphology of selected brain structures (Luders, 2015; Fox, 2014; Xue, 2011; Vestergaard-Poulsen, 2009; Lazar, 2005;). 

How can these practices, developed by humanity for thousands of years (Easwaran, 2009), be utilized to bring about accelerated personal realization? In yogic practices, the awareness connectome is invited to forge links between high cortical functions and deep visceral systems. In this process, the autonomic nervous system becomes less robotic, as it is gradually invited into the domain of the sentient self. Since tapping into awareness networks via meditation increases the proliferation of neuronal cellular elements in selected brain structures, can we posit that such practices promote the genesis of specialized cell subtypes destined to produce awareness, namely neurons that, active in vast networks, could be called “awareness neurons?”

Studies point to the capacity of psychedelics to promote neuroplasticity. This is achieved by dendritogenesis, synaptogenesis and the expression of plasticity-related genes via brain-derived neurotrophic factors. These authors privilege the prefrontal cortex and hippocampus as sites of greatest psychedelic-induced fluidity (Calder, 2023).   

In practices such as Zen Buddhism (Suzuki, 2020), and the “mental yogas,” as in Raja Yoga and Kriya Yoga, it becomes possible to attain coveted states of self that can distinguish awareness’ content from its fundamental nature. In the profound experience of such special states, there are no thoughts, no emotions and no memories, simply the raw energy of consciousness. This state is named “Pure consciousness” (Shear, 1999). Experiencers attempting to describe this phenomenon use words like ineffable and transcendental (Bucke, 2010). Western languages have not yet ascribed words to these special states of qualia. One can appreciate, however, that when experiencing is centered on the very energy that creates it, reports will often use terms that invoke the universal, cosmic and divine.

Variations of “pure consciousness” states are regularly encountered in psychedelic therapy sessions as they can in the deeper stages of meditative hypnosis (Sunnen, 2013). During these times, therapist/patient communications may become substantially altered, with long pauses and silences, the use of phrases rather than completed sentences and novel choice of words. Those episodes represent times of greatest neuro-fluidity and therefore offer opportunities for establishing new and lasting modifications of personal constructs.  

Experiencing “pure consciousness,” can be as impactful as it is transformative because it teaches those notions of selfhood derived from a lifetime of family and social interactions, may no longer satisfy the quest for personal meaning. Self-concepts, emerging after experiencing “pure consciousness,” connect to a seemingly more immutable base. The experience is therapeutic in the sense that it couples the sense of self to a more fundamental essence, namely personal primal life energies, which, at their base, remain perennially positive.   

Psychedelics in psychotherapy and their augmentation with psychosomatic techniques 

Psychotherapy basically seeks to assist in the transformation of states of being, from “lesser” subjective states to “higher” ones. Lesser states are usually ones of psychic malaise and existential pain, dysphoria in myriad forms, from persistent depressions and paralyzing anxieties to distressful self-image issues. The coveted states of consciousness, on the contrary, imply relief and emancipation from these painful states.

Psychoanalysis, as a technique of personal change, undoubtedly holds the record for its tolerance for time in achieving coveted transformations. Its invaluable discoveries, however, opened portals leading to the understanding of the unconscious mind’s fascinating complex mechanisms (Ellenberger, 1970).  Modern psychotherapies have worked to become more quickly productive. While novel therapies claim faster improvements, the quest for transformative therapeutic results spawns poignant questions: What actualizes systemic personal change? And in the context of new insights on neurodynamics, can the revelations gleaned from psychedelic clinical research assist in this task? 

To accelerate therapeutic results, innovative approaches are integrating the assistance of augmenting therapies such as medical hypnosis (Sunnen 1999), meditation, yoga and Autogenic Training. These facilitators of well-being and therapeutic change become important in preparing patients for the full potential of their psychedelic experience.

On preparing patients for psychedelic assisted therapy 

Preparation for psychedelic therapy greatly enhances successful outcome. In a context of understanding the patient’s psychodynamics and sources of psychic distress, a clear delineation of therapeutic objectives is agreed upon in a collaborative patient/therapist dyad. Indeed, patients encountering psychedelic-induced confusion, who were then gently refocused on their goals, were invariably returned to calmer, more productive states.  

Prior to embarking on psychedelic assistance, it is suggested that patients receive training in a selected mind-body discipline, may it be self-hypnosis (DeBetz, 1985), yoga, meditative breathing, progressive relaxation, meditation, even Tai Chi and Qigong.

Herewith suggested is Autogenic Training, sometimes called “Western Yoga,” which offers advantages for the fact that it has quantifiable progress objectives. Developed by European clinical researchers more than a century ago, Autogenics initially sought to replicate the phenomena observed in deep hypnosis, without the assistance of a hypnotist (Luthe, 1965). Deep autonomic nervous system relaxation is a priority goal for this practice, but like other yoga systems of personal growth, it ultimately invites higher ego-syntonic experiencing of self (Sunnen, 2021).

A calm-down may be needed during a psychedelic experience. The therapist, familiar with the patient’s chosen relaxation method may suggest it be practiced during the session. The therapist may also propose guided imagery, or a hypnotically induced calming trance state. Very effective are physiological breathing techniques; they too will need to be learned by the patient before exploring psychedelic therapy. 

Conclusion

Acting at the interface of the physical body and its consciousness, psychedelic agents embody unique properties to modulate perception, cognition, mood and importantly, the experiential configuration of self. Via activation of 5-HT2A cortical circuitries and their subcortical ramifications, psychedelics link to the elaboration of sentience. Mounting evidence suggests that the therapeutic effects of psychedelics is linked to their capacity to stimulate neuroplasticity. The mind-body problem remains unsolved but the opportunities for its elucidation are increasing.  

Psychological manifestations of activated 5-HT2A circuitry in cortical connectomes manifest as fluidities of selfhood that offer opportunities for accelerated therapeutic transformations. Techniques that develop heightened entente between mind and body easily complement psychedelic psychotherapies. Examples include medical hypnosis, meditation, progressive relaxation, yoga, mindful breathing and Autogenics.

Psychedelic psychotherapies require planning. An understanding of patients’ psychodynamics and a clarification of objectives increase their productivity and successful outcomes. Embracing the promise of these therapies represents a dynamic movement toward an enlightened vision for their therapeutic promise.

A successful psychedelic experience will be expressed by positive ripple effects on several dimensions of functioning, in a context of a calmer, disentangled and stronger qualia, all beckoning a brighter, even more joyous personal cosmology.

References

Aixalà M. (2022). Psychedelic Integration: Psychotherapy for Non-Ordinary States of Consciousness. Synergetic Press, London.

Alter, T., Howell R. (2011). Consciousness and the Mind-Body Problem. Oxford University Press.

Ballentine, G., Freesun-Friedman, S., Bzdok, D. (2022, March 16). Trips and neurotransmitters: Discovering principled patterns across 6850 hallucinogenic experiences. Science Advances, Vol. 8, Issue 11.

Bazinet, V., Hansen, J., Misic, B. (2023). Towards a biologically annotated brain connectome. Nature Reviews Neuroscience, Vol 24, 747-760.

Blumenfeld H. Neuroanatomy Through Clinical Cases, Second Ed. (2010). Sinauer Assoc. Publishing Co., Sunderland MA.

Brazis P., Masdeu J., Biller J. (2010). Localization in Clinical Neurology. Sixth Ed., Lippincott Williams & Wilkins.

Bucke R., (Ed.) (2010) Cosmic Consciousness: A Study in the Evolution of the Human Mind. Martino Publishing, Mansfield Centre, CT.

Calder, A., Hasler, G. (2023). Towards an understanding of psychedelic-induced neuroplasticity. Neuropsychopharmacology, 48, 104–112.

Carhart-Harris R, Nutt D. (2017). Serotonin and Brain Function: A Tale of Two Receptors. J. of Psychopharmacology, Vol. 31, Issue 9.

DeBetz, B., Sunnen, G. (1985). A Primer of Clinical Hypnosis. PSG Medical Publishers, Littleton, MA.

Doss, M., Madden, M., Gaddis, A., et al. (Feb 2022) Models of psychedelic drug action: modulation of cortical-subcortical circuits. Brain. Vol 145, Issue 2, 441-456.

Duan, X., Kang, E., Liu, C., et al. (2008). Development of neural stem cells in the adult brain. Curr Opin Neurobiol, 18(1), 108-115.

Easwaran, E. (2009). The Upanishads. Nilgiri Press, 2nd Ed.

Ellenberger, H. (1970): The Discovery of the Unconscious. New York, Basic Books.

Fox, K., Nijeboer, S., Dixon, M. et al. (2014). Is meditation associated with altered brain structure? A systematic review and meta-analysis of morphometric neuroimaging in meditation practitioners. Neuroscience and Behavioral Reviews, 43, 48-73.

Funahashi, S. (Sept. 2008). Neural mechanisms of decision-making. Brain Nerve, 60(9), 1017-27.

Gage, F., Temple, S. (2013). Neural stem cells: Generating and regenerating the brain. Elsevier.

Gammel, T., Alkadaa, L., Saadon, J., et al. (June 2023). Brain Circuitry of Consciousness: A Review of Current Models and a Novel Synergistic Model with Clinical Application. Neurosurgery Practice, 4(2), 00031.

Hansen, J., Shafiei, G., Markello, R., et al. (2022). Mapping neurotransmitter systems to the structural and functional organization of the human neocortex. Natural Neuroscience, 25, 1569–1588). 

Hatzipantelis, C., Olson, D. (2024). The Effects of Psychedelics on Neural Physiology. Annual Review of Physiology, Vol. 86, 2024.

Hölzel, B., Carmody, J., Vangel, M., et al. (Jan. 30, 2011). Mindful practice leads to increases in regional gray matter density. Psychiatry Research, 191(1), 36-43.

Huxley A. (2009). The Doors of Perception. Harper Perennial Modern Classics.

Kandel, E., Koester, J., Mack, S., et al. (2021). Principles of Neural Science. Sixth Ed. McGraw Hill/Medical.

Kelmendi, B., Kaye, A., Pittenger, C., Kwan, A. (Jan 24, 2022). Psychedelics. Current Biology, 32, 55-71.

Kwan, A., Olson, D., Preller, K., Roth, B. (2022). The neural basis of psychedelic action. Nature Neuroscience, Vol. 25, 1407-1419.

Laureys, S., Gosseries, O., Tononi, G. (2016). The Neurology of Consciousness. Second Edition. Academic Press, Elsevier.

Lazar, S., Kerr, C., Wasserman. R, et al., (Nov. 28, 2005). Meditation experience is associated with increased cortical thickness. Neuroreport.16(17), 1893-1897.

Luders, E., Kurth, F., Cherbuin, N. (2015). Forever young(er): potential effects of long-term meditation on gray matter. Frontiers in Psychology, 5:1551.

Luthe, W., Schultz, J. (1969). Autogenic Training. Grune and Stratton, Inc., New York.

James, W. (1988). The Varieties of Religious Experience. Library of America.

Kandel, E., Schwartz, J. (Eds). (2021). Principles of Neural Science, Sixth Edition. The McGraw Hill Companies, Inc.

Pałasz, A., Menezes, I. & Worthington, J. (2021). The role of brain gaseous neurotransmitters in anxiety. Pharmacol Rep, 73, 357–371. 

Penfield, W. (2015). The Mystery of the Mind: A Critical Study of Consciousness and the Human Brain. Princeton University Press.  

Plum, F., Posner, J. (1982). The Diagnosis of Stupor and Coma. Oxford University Press.

Pollan, M. (2018). How to Change Your Mind. Penguin Books.

Rinpoche, D., Zahler, L., Rinpoche, L. (1983). Meditative States in Tibetan Buddhism, 2nd Ed. Wisdom Publications.

Shear, J., Jevning, R. (1999, 1 Feb). Pure consciousness: scientific exploration of meditation techniques. J of Consciousness Studies, Vol 6, Numbers 2-3.

Stine, E., Glasser, M., Harms, M., et al. (2021). The Human Connectome Project: A Retrospective. Neuroimage. Elsevier, Vol. 244. 

Sunnen, G. (1999). What is Hypnosis? In: Temes, B. “Medical Hypnosis: An Introduction and Clinical Guide,” published in the “Medical Guides to Complementary and Alternative Medicine” Churchill Livingstone, New York.

Sunnen, G. (2019). Experiencing “Pure Consciousness:” A catalyst in psychotherapy? http://www.triroc.com/sunnen/topics/experiencepureconsciousness.htm

Sunnen, G. (2021, June). Autogenic Training as Preparation for Yoga Practice. Yoga Magazine. London. Yoga June 2021 - Gerard  Sunnen-6.pdf

Sunnen, G. (2013). Spiritual Epiphanies During Hypnosis. Triroc.com/sunnen  http://www.triroc.com/sunnen/topics/spiritualepiphanies.htm

Suzuki, S. (2020). Zen Mind, Beginner’s Mind: 50th Anniversary Edition. Shambala.

Van Elk, M., Yoden, D. (2022, Sept). Pharmacological, neural, and psychological mechanisms underlying psychedelics: A critical review. Neuroscience and Behavioral Reviews, Vol 140.

Vargas, M., Dunlap, L., Dong, C. (2023, 16 Feb). Psychedelics promote neuroplasticity through the activation of intracellular 5-HT2A receptors. Science, Vol 379, Issue 6633.

Vestergaard-Poulsen, P., van Beek, M., Skewes, J., et al. (Jan 28, 2009). Long-term meditation is associated with increased grey matter density in the brain stem. Neuroreport, 20(2): 170-174.

Vilaró, M., Cortés, R., Mengod, G., Hoyer, D. (2022). Distribution of 5-HT receptors in the central nervous system: an update. Handbook of Behavioral Science, Vol 31, 121-146.

Vincent, S. (2000). The ascending reticular activating system - from aminergic neurons to nitric oxide.  J Chemical Neuroanatomy, 18 (1-2), 23–30.

Watts, A. (2013). The Joyous Cosmology: Adventures in the Chemistry of Consciousness. New World Library, Second Ed. 

Xue, S., Tang, Y., Posner, M. (2011, Aug 24). Short-term meditation increases network efficiency of the anterior cingulate cortex. Neuroreport. 22 (12), 570-574. 

Yogananda, P. (1946). Autobiography of a Yogi. The Philosophical Library, Inc., New York.

………………………………………………………………