
In this book Zen Buddhism becomes the opening wedge for an extraordinarily wide-ranging exploration of consciousness. In order to understand which brain mechanisms produce Zen states, one needs some understanding of the anatomy, physiology, and chemistry of the brain. Austin, both a neurologist and a Zen practitioner, interweaves the most recent brain research with the personal narrative of his Zen experiences. The science is both inclusive and rigorous; the Zen sections are clear and evocative. Along the way, Austin examines such topics as similar states in other disciplines and religions, sleep and dreams, mental illness, consciousness-altering drugs, and the social consequences of the advanced stage of ongoing enlightenment.
Be warned though; it is a huge, dense and detailed book since the author is both a neuroscientist/neurologist and a zen meditation practitioner himself.
Another good resource is the book "Zen and the Brain".
And this interview with Daniel Ingram mentions some fascinating research on his own capacities developed in meditation: https://www.youtube.com/watch?v=APOKB59pVpE
Zen and the Brain by James Austin details his study of Zen monks brains which revealed this breathing-stress connection scientifically decades ago.
If I remember correctly, the exhale is especially important to triggering certain relaxation states; brains of monks who were especially focused on long exhales were appreciably different from other monks.
Zen and the Brain – Toward an Understanding of Meditation and Consciousness By James H. Austin https://mitpress.mit.edu/books/zen-and-brain (Austin is a professor emeritus of neurology, neurologist, researcher, and Zen practitioner)
Austin covers the effect of psychedelics and their effects relative to meditation but nothing about meditation on drugs if I remember correctly. The personal parts are easy to read. Neuroscience and chemistry are much harder. The reference and source notes section is valuable if you are doing research.
* "Zen and the Brain" (written by a meditation practising neurologist)
* "The Buddha Brain" (about the neurological/physiological background of a couple of buddhist principles)
