During a raid on an illicit drug lab, a man threw a vial full of liquid phencyclidine, or PCP, in the face of a Los Angeles police officer.

The policeman immediately lost motor coordination, began hallucinating and demonstrating schizophrenia-like symptoms. It took several of his colleagues to get him to a hospital.

PCP so crazed a young woman recently in a Washington hospital that she literally tore the skin off her face with her fingernails because she believed she was covered with noxious insects. A man in Los Angeles tore out his own eyeballs. The drug is implicated in up to half of all adult admissions to St. Elizabeths Hospital.

But an antidote that blocks at least the long-term brain-ravaging effects of PCP may be close at hand. A research team lead by Dr. Thomas O'Donohue, chief of the Unit on Neuroendocrinology in the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS), may have found a compound that could be used against the drug in the near future in emergency rooms and psychiatric wards of the nation's hospitals.

O'Donohue is something of an expert on PCP because he has identified and isolated a phencylidine-like chemical in the brain. (Some of his work is featured in the final episode of the PBS series "The Brain," which airs Wednesday, Dec. 5 at 8 p.m., Channel 26.)

The brain chemical, says O'Donohue, is a neuropeptide, one of a newly discovered class of neurotransmitters -- electro-chemical messengers between brain cells -- that govern all functions of mind and body. The brain's own PCP appears to be related to learning and memory.

With the discovery of a PCP antidote, says O'Donohue, "we may not only be treating a problem in modern society, but if this compound could block the PCP system in the brain, it could lead to treatments for schizophrenia, Alzheimer's disease, normal memory loss."

Since the PCP system seems to be involved in learning and memory, the brain's PCP-like chemical may turn out to be a learning enhancer.

But the synthetic -- better known by such street names as "angel dust," "lovely," "love boat" or even sometimes "the key to St. E." -- is not so useful.

When PCP is inhaled, injected, ingested, or smoked (sprayed on parsley or marijuana) it switches off the functions of the neocortex -- the most recently evolved part of the brain, the part which gives us our humanity, intellect, self-awareness and keeps our "animal" brain, the seat of primitive instinct and emotions, in check.

Without the inhibitions of the neocortex, uncontrolled, unpredictable, irrational violence, fury and terror reign supreme. Such uncontrollable behavior happens in many PCP users -- even those, like the Los Angeles policeman, whose contact is brief and unintentional.

"He is better," says LAPD spokesman Lt. Dan Cook, but has "some residual problems," even after several months.

Two other LAPD officers assigned to weighing confiscated PCP also had serious toxic-behavioral reactions to the drug. As a result, confiscated PCP now is kept in a separate room at police headquarters and no one enters without gloves and a gas mask.

Sometimes PCP side effects are permanent -- even after a single use in a sensitive person, and, says O'Donohue, "there are many who are diagnosed right then as schizophrenics and are maintained on antipsychotic therapy and sometimes hospitalized for years. You'd think if the kids on the street knew a little more about this, they'd hesitate. Because it's not hype."

Nevertheless, research has intensified on PCP not only to combat its abuse, but because of the real possibility that the chemical can be tamed into what O'Donohue calls "the perfect anesthetic," perhaps even a "cognitive enhancer" -- something that makes you smarter.

Phencyclidine was chemically synthesized as an anesthetic about 20 years ago along with ketamine, a very similar drug, and it looked briefly as if they would drive all existing anesthetics off the market. They seemed to be extremely safe, have few side effects, and leave no grogginess or nausea. The trouble was, researchers quickly learned, that about 30 percent of the patients had bizarre hallucinations.

With today's ongoing explosion of brain research, it is not surprising for a brain researcher to discover that a chemical can both ravage the mind or make it smarter.

Besides the social question about PCP, research has been driven by the quest for cognitive enhancers, O'Donohue says. "What excites the pharmaceutical companies is the unlimited market. What student, what scientist, what physician, what professional, what reporter wouldn't take one? I've never taken a Valium, but I'd take a cognitive enhancer every day . . ."