D: Ken Russell. S: Sidney Aaron [Paddy Chayefsky]. P: Howard Gottfried, Daniel Melnick, Stuart Baird. Cast: William Hurt, Blair Brown, Bob Balaban, Charles Haid. UK dist: Warner Bros.

Compelling, exciting and profoundly frightening, Altered States boasts possibly the most radical and brilliant concept in all SF, and certainly the most terrifying: the possibility that man might find a way to unlock the numberless aeons of evolutionary data stored in the human genetic code, and pursue the chain of creation back to its primordial source, the Original Self – God? – glimpsed in mystical experiences through the ages. Ideas don’t grow much bigger than this.

Inspired by childhood memories of eidetic visions, whizzkid scientist Dr Jessup (William Hurt, in a terrific debut) has found the ideal experimental subject to realise his obsessive dream of confronting the infinite: himself. Fascinated by the hallucinatory images flooding his mind in the amniotic gloom of a sensory deprivation tank, Jessup is soon frustrated by the limitations of his principal apparatus, the human brain. The breakthrough comes, years later, when he participates in a mystical rite conducted by a remote Mexican tribe; and Jessup is soon ingesting a powerful hallucinogen to boost his lengthy sessions alone in the isolation tank. Success looms: the genetic template is breached, and human morphology becomes suddenly – alarmingly – fluid. Jessup watches helplessly as his own body undergoes a succession of agonising transformations – regressing first into a savage hominid, and ultimately (in an unprecedented, soul-chilling finale) into a writhing, screaming, seething lump of cosmogenetic protoplasm.

A quasi-Ballardian voyage into “inner space”, culminating in a psychedelic riot to rival Kubrick’s Ultimate Trip, Altered States dares to confront us with the sheer enormity of the multi-billion year history locked in the deepest, most inaccessible part of ourselves – and with the shrieking void that awaits those who attempt to crack the seals. Playwright and scenarist Paddy Chayefsky (Network) based his 1977 novel on the experiments of Dr John C. Lilly, distinguished brain researcher and pioneering isolation tank aquanaut, and penned his own script adaptation for flamboyant auteurist-turned-gun-for-hire Ken Russell (an inspired choice, though not – by the director’s own cheerful admission, and by some distance – the studio’s first). Their working relationship, though not exactly harmonious on set, produced one of the most intelligent SF movies in the genre’s uneven history; but in one of the more mind-boggling acts of writerly pique, Chayesfsky chose to sign the film with a thinly disguised pseudonym (“Sidney Aaron” – his first two given names) after quarrelling with the director over some trivial emendation of his text. Russell’s film follows the novel almost to the letter, so only God (or Paddy’s Original Self) can say what goaded Chayefsky to chuck his toys out of the pram on this occasion.

The tale’s own ancestral origins are easy enough to trace. At root, it’s an elaboration of the Jekyll and Hyde theme of chemically-induced atavism, jettisoning Stevenson’s Manichean morality fable in pursuit of something far more abstractly fascinating – the tortured birth pains of Life itself, a still-living memory buried under billions of years of evolutionary happenstance. In short: the most gripping time- travel story ever conceived, where the time machine is your own body. Deeply frightening stuff, which could easily have seemed merely ridiculous (cf. Jack Arnold’s imaginatively dippy Monster on the Campus [1958], where a college professor inadvertently adds a few flakes of vintage Coelacanth to his favourite shag and promptly regresses into a drooling Neanderthal); but Mad Ken is clear-headed enough to understand that stone-cold sobriety is the key to handling this material successfully, restricting his bursts of imaginative ferocity to a series of stunningly-realised hallucinatory episodes. Here Russell dips unambiguously into the visual world of the Surrealists (the small Delvaux poster in Jessup’s home suggesting how art can both reflect and inform the visionary flights of the mind), with the expected distortions of Biblical symbolism: a burning crucifix ascends into a racing sky, a goat-headed Christ writhes on the cross and thousands of naked sinners topple into a fiery underworld. Editing and sound design are first-rate: like the tormented Dr Jessup, the viewer senses his skull splitting its sutures under the ferocity of Russell’s visionary onslaught, reducing him finally to a condition of abject primal terror. John Corigliano’s brooding score draws us deep inside the menacing heart of the tale, although how much of its effectiveness can be credited to avant-garde composer Pierre Henry’s “Le Voile D’Orphée” (name-checked in the closing titles) I couldn’t say, being unfamiliar with the work.

Before Chayefsky and Russell, only Kubrick and Clarke mustered courage and talent enough to tackle ideas on this galactic scale; and while Altered States may lack the enigmatic grace of 2001: A Space Odyssey (1968), its ambitions are no less astonishing. But all things must end; and like a tracer bullet, Russell’s film describes a magnificent and fiery arc before falling exhaustedly to earth. Perhaps inevitably, the resolution (identical in novel and film) sounds a quiet note of anticlimax, with the author’s thematic purpose revealing itself too transparently: it’s fractionally too neat, too emotionally tidy. Over the course of his narrative Chayefsky’s graph leaps from the human, to the cosmic, then drops again to the human: like coming down from a synapse-rending high, it’s hard not to find the sudden contraction of scale disappointing, and Jessup’s epiphany perhaps needed some additional fine-tuning between writer and director to be totally convincing. But these are minor niggles; a film so superabundantly blessed with mind-expanding concepts and visual brio can certainly survive a momentary dip towards imperfection. Films rarely imprint themselves so indelibly on the imagination, or provide such enormous scope for speculation. It may end small, but Altered States leaves us thinking big.