Instead of simply raving about this extraordinarily brilliant piece of literature, let me get specific right from the get go.
First, Leary's essay on "Cyberphenomenology" is a thought experiment for the ages. In a few short pages, Dr. Leary leads you gently to the obvious conclusion that consciousness, (Dr. Leary, ever the scientist, doesn't really believe in "souls;" those are the department of his more woo-woo ex-compatriot Ram Dass), that witnessing phenomenological center of being, is not limited in space-time to the brain. I'd say that might provide some comfort for somebody about to shuffle-off their mortal meat-suit.
Given Leary's materialist bent as a serious scientist (yeah, he is a scientist--almost to a fault--no matter what else you want to say about him) this really is a shocking philosophical gem with pseudo-idealist/quasi-immaterialist implications. Leary is Irish, after all. And this is a work that Bishop Berkeley and Terrence McKenna alike were blessing from above. If you are at all interested in phenomenology, in consciousness studies, or in the mind/body problem, you've got to read Cyberphenomenology: You are Where You Think You are. It's profound simplicity is going to rock your world. These few pages alone are more than worth the cost of the book.
Secondly, and let me flash some credentials at you here, I am a Graduate Psychology student and my focus has been very much on "object relations" psychology and in Developmental Psychology. Developmental Structuralism took a hit in the 60s when everyone went loopy and fell for the performative contradiction (hypocritical hogwash) that is "post-modern post-structuralism." However, Developmental Psychology has been making a comeback of late with writers like Robert Keegan (The Evolving Self: Problem and Process in Human Development) and, most recently, Don Beck (Spiral Dynamics: Mastering Values, Leadership and Change), making the case for a post-post-modern "re-construction." All views are not equally valid. Hitler was not as evolved as Ghandi; hierarchies exist in nature and in human personality; so just deal with it. Piaget, Loveinger, Kohlberg, and Graves have all scientifically demonstrated that human consciousness evolves through sequential (and predictable) stage-structures.
What I have to tell you is that Tim Leary's "8-Circuit Model of Human Development," which is presented in Your Brain Is God but much more fully and beautifully worked out in Design For Dying, is the most complete and thorough model of structural development ever conceived. Critics (what the young people these days call "haters") all too easily fall into forgetfulness about Leary's credentials. The man was TEACHING PSYCHOLOGY AT HARVARD, for God's sake. He is dazzlingly brilliant. Whether you think it was wise for everyone and his brother to drop acid and make love with herpes-ridden strangers in Golden Gate Park (and who does?) or not, give the man his due. Leary escaped from high security prisons several times. He was no dunce. (The real dunces were the prison psychologists who gave Leary psych tests that HE HIMSELF HAD HELPED DESIGN). On cognition alone, Leary ranks as one of the Twentieth Century's epic intellects--right up there with Einstein and Crick and Gandhi and Goodall.
This 8-Circuit Model, or "Leary Theory" for short is proof positive. It holistically integrates the development of the subjective mind with the development of objective neurology. It addresses the philogenetic evolution of the species as well as the object-relations evolution of the individual. It also includes the cultural and social ramifications and implications that manifest at each successive stage.
Lastly, and this will offend the prudes and the puritans, Leary explains for good or for bad, which molecular metabolites light up which neuro-circuits. A lot has been said about drugs and their inability to provide peak or "peek" experiences of higher developmental stage-structures, but empirical science says otherwise. Watch kids at raves on MDMA "peek" experiencing higher developmental levels in the moral line or inter-personal line.
And even in cognitive lines, many epiphanies have been triggered by LSD from Francis Crick's vision of the double-helical structure of DNA to Dan Akroyd's idea for a little show called Saturday Night Live, from Kary Mullis' invention of Polymerase chain reaction techniques for copying DNA sequences, to Phil Jackson's revelation about the Texas Triangle offense, (phenethylamines and) tryptamines have provided (temporary) developmental shifts. To deny this is farcical. And don't even get me started on shifts in James Fowler's Spiritual line of development.
And drugs can drop you down to lower levels of personal or evolutionary development as well, of course. Heroine can return you to the state of the neonate..or even the amoeba!
Given that the heart of shamanism has always been that medicine men (and women) could travel upward to heaven realms and downward to hell realms, it seems that Leary has, with his 8-Circuit Model, provided a detailed neuro-biochemical description of shamanism (and mysticism).
There are many touching stories by and about Tim in this book. (MY favorite involves Tim giving away his automobile to a stranger because he was late to a Dodger game.) There is wisdom about Death and Dying. Anyone who is about to give up the ghost or anyone has a loved one preparing to depart absolutely must read this book.
However, for my money, as a Graduate Psychology student, it is Leary's Cyberphenomenological thought experiment and his astoundingly complete model of human development that scholars will be talking about hundreds of years from now. Amazing stuff, truly.
Buy the book.