What if there was a pill you could take that would change you from an introvert into the extrovert you always wanted to be? Or if there were readily available capsules to raise your spirits when you wanted to feel "up," or to ease you into blissful relaxation when that was your aim? In Receptors, Dr. Richard M.

Restak, acclaimed author of The Brain and The Mind, leads us on a fascinating - and sometimes disquieting - scientific adventure into the remarkable new advances in brain research that are making such transformations a reality.

He begins this search in the primeval regions of Central and South America, where for countless years native peoples have employed "sacred plants" to open new doors of perception by literally altering their minds. Along the way he introduces us to the early pioneers in the development of drugs that made possible the treatment of many mental disorders.

And he takes us into the laboratories of today's molecular chemists and neuroscientists who are creating drugs that will change our brains in ways that only a few years ago seemed the stuff of science fiction.

Dr. Restak lucidly describes the extraordinary discoveries in mapping the brain and deciphering the functions of neurotransmitters, the chemical molecules that convey messages between neurons, and receptors, the sites on the target neurons to which these messenger molecules attach. Communication is their function, and it is now clear that disturbances that affect this communication underlie not only mental illnesses but lesser conditions like performance anxiety or hyperactivity.

Indeed, it now seems clear that neurotransmitter-receptor interactions have a critical role in normal as well as aberrant behaviors. They lie at the root of basic personality and temperament, playing an important part in making us moody or exuberant, shy or outgoing, passive or assertive.

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Most compelling of all, Dr. Restak shows how recent discoveries are making it possible for scientists to alter the brain with "designer drugs" that hold out the possibility of slowing down or preventing the decline in memory that typically accompanies aging; reversing substance addiction; relieving, and ultimately perhaps even curing, such brain diseases as schizophrenia, Parkinson's, and Alzheimer's.

The promise of drugs like these raises no qualms; they are as unambiguously beneficial as antibiotics for a physical ailment. But also on the horizon is the very real likelihood that it will be possible to "design" our own brains, enriching memory, enhancing intelligence, heightening pleasure, concentration, and creativity, and changing our basic personalities. How are we to assess chemical substances like these? How do we cope with the ethical dilemmas such godlike power poses?

1. From the levitating ointments of medieval "witches" to the magic mushrooms of southern Mexico, from the LSD of the psychedelic age to the latest discoveries of today's psychopharmacologists, Dr. Restak provides a vivid and lucid account of humanity's unceasing effort to decode the mysteries of the human brain - mysteries whose ultimate solutions grow daily more imminent.