Using a sensory depravation tank, Dr. Eddie Jessup (William Hurt, in his screen debut) studies altered states of consciousness by submitting himself to trance inducing techniques. His first time in the tank, Jessup claims to have experienced religious allegory. His colleague (Bob Balaban) is uncertain about what it is they’re looking for. At a party, a physical anthropology student named Emily (Blair Brown) approaches Jessup. Before long, the wiz kids are having sweaty sex on her sofa.

Jessup tells her that as a child, he used to see visions of angels and saints. He’s obsessed with unraveling the mysteries of life – whether the point to all our suffering is just more suffering – and believes the key to this secret is locked inside the limbic system of the brain, which stores six billion years of memory. To access it, Jessup travels to Mexico, where a tribe of Hinchi Indians uses the mushroom amanita muscaria – a powerful psychedelic – in their rituals.

Jessup starts up his tank experiments again, this time under the influence of the mushroom and under the eye of a skeptical doctor (Charles Haid from Hill Street Blues). Jessup comes out of the tank with blood on his mouth. He claims to have regressed into a furred humanoid creature – the first man – and believes the blood to belong to the goat he was eating. Soon, his genetic structure begins to get strange.

Altered States was a 1978 novel by the renowned playwright and screenwriter Paddy Chayefsky, who won an Academy Award for Network. The novel – his first foray into fiction – was loosely based on the experiments of Dr. John Lilly in the 1950s. Lilly at one point ingested the psychedelic ketamine and isolated himself in a sensory depravation tank to explore human sub-consciousness. He stated that a colleague of his suddenly “became” a chimp, and later claimed to have regressed into a pre-hominid creature.

Chayefsky adapted his novel into a screenplay, which Arthur Penn was hired by Columbia Pictures to direct. Chayefsky was contractually guaranteed to have his dialogue adhered to word for word without exception. By the middle of production, Penn had had enough of this, and quit. Visual effects supervisor John Dykstra followed him out the door. Columbia scuttled the project, which Warner Bros. then acquired. After searching in vain for someone willing to work with Chayefsky, the studio settled on Ken Russell.

Russell fulfilled his obligations to Chayefsky by instructing the actors to mutter, zip through or shout the scientific or spiritual jargon. Chayefsky wasn’t amused and before even getting a look at the finished film, took his name off it, employing the pseudonym “Sidney Aaron”. Chayefsky ended up spending the last year of his life publicly disowning Altered States to anyone who would listen. Critics weren’t listening, and while many of them praised the film’s weirdness and entertainment value, it came and went from theaters.

This film may be one of the best challenges to the “auteur theory,” the delusion held by some scholars that movies are the work of a single author, the director. With this movie – a wild mash up of sci-fi, horror, character drama and head trip – it’s impossible to know where Penn’s version ends and Russell’s begins. And it doesn’t matter. Altered States works almost as brilliantly as The Exorcist or Alien. It’s intelligent, scary, thought provoking, at times silly, but above all, features exceptional work from its cast and crew.

It’s difficult to know whether Chayefsky intended Altered States to be taken seriously, but the film is abound with big ideas and far out hypotheses about evolution, the cosmos and what it means to be human, the hallmarks of all great science fiction. Thanks in large part to the casting of William Hurt, Blair Brown and Bob Balaban, the characters in the movie come across as adults, and relate to each other as adults, as opposed to horror movie staples.

The most noted characteristic of Altered States is its hallucination imagery, which is beyond bizarre. A six-eyed lamb is sacrificed on an ancient book, souls burn in the inferno of hell, Hurt and Blair crumble to dust. While the movie doesn’t end up with a whole lot of places to go, the sequence in which Jessup reverts to a primitive humanoid and terrorizes a janitor in a university basement is outright spooky. Drew Barrymore made her screen debut here, appearing briefly as one of Jessup’s kids.