The function of the brain and nervous system and sense organs is in the main eliminative and not productive.

- Henri Bergson

There are two states in which man arrives at the rapturous feeling of existence, namely in dreaming and in intoxication.
- Nietzsche, The Dionysian Worldview,

By wine or opium we can intensify and considerably heighten our mental powers, but as soon as the right measure of stimulus is exceeded, the effect will be exactly the opposite.

- Schopenhauer

Without the eye there can be no sensations of vision, and without the brain there could be no recollected visible ideas; but neither the optic nerve nor the brain can be considered as the percipient principle—they are but the instruments of a power which has nothing in common with them. …

The desire of glory, of honour, of immortal fame, and of constant knowledge, so usual in young persons of well-constituted minds, cannot, I think, be other than symptoms of the infinite and progressive nature of intellect.

- Humphry Davy, from Consolations in Travel or The Last Days of a Philosopher

Humphry Davy on laughing gas (nitrous oxide):

"I lost all connection with external things; trains of vivid visible images passed through my mind and were connected with words in such a manner as to produce perceptions perfectly novel. I existed in a world of newly connected and newly modified ideas … I exclaimed to Dr Kinglake, “Nothing exists but thoughts!” …

I have often felt very great pleasure when breathing it alone, in darkness and silence, occupied only by ideal existence."

Eleusinian Mysteries

An account of Plato, attending an event called Eleusinian Mysteries held at Eleusis, a dozen miles or so from Athens, which included kykeon,a beverage of water and barley sometimes flavored with mint or thyme:

"[W]ith a blessed company—we following in the train of Zeus, and others in that of some other god—… saw the blessed sight and vision and were initiated into that which is rightly called the most blessed of mysteries, which we celebrated in a state of perfection … being permitted as initiates to the sight of perfect and simple and calm and happy apparitions, which we saw in the pure light, being ourselves pure and not entombed in this which we carry about with us and call the body, in which we are imprisoned like an oyster in its shell."