IN "SAD BRAIN, HAPPY BRAIN" (HEALTH FOR LIFE, Oct. 6) Dr. Michael Craig Miller, editor in chief of the Harvard Mental Health Letter, shares the mental myopia of so many of his collegagues: that the whole can be understood by observing the parts. In dismissing the intelligence of a brain cell as no smarter than an amoeba, he dismisses one of the greatest wonders nature has come up with in 3 billion years of evolution - a single human cell can simultaneously manage 10,000 chemical reactions while coordinating this activity with the other 10 trillion cells in our bodies. When Miller can explain how the cell manages to do this, then he and his colleagues may be ready to discuss faith, love and understanding.

MICHEL MORTIER ZUG, SWITZERLAND

IT IS, OF COURSE, IN THE BEST INTERests of neuroscience to declare the physical brain to be the origin of all behavior. For myself and others, something intangible (call it mind or spirit) is nevertheless at our disposal, overriding fear with insights and peace of mind that transcend the “fully engaged” brain. Ironically, it is only when the brain becomes quiet that this additional dimension of consciousness is discovered.

ROBERT MAURICE COVINGTON, LOUISIANA

WHILE I ENJOYED THE ARTICLE “SAD Brain, Happy Brain” I fear it may engender antipathy toward cognitive neuroscience. The author allows that many people are “put off by the notion that such rich experiences could be reduced to mechanical or chemical bits” but he does not adequately address these fears. Research has shown that these “chemical bits” are as mysterious as consciousness, and, indeed, history has shown that science generally reveals more mysteries than it explains.

SHANNON SYNAN BELCHERTOWN, MASSACHUSETTS