Researchers have established that when people are mentally engaged, biochemical changes occur in the brain that allow it to act more effectively in cognitive areas such as attention and memory. This is true regardless of age.
People will be alert and receptive if they are faced with information that gets them to think about things they are interested in. And someone with a history of doing more rather than less will go into old age more cognitively sound than someone who has not had an active mind.
Many expert are so convinced of the benefits of challenging the brain that they are putting the theory to work in their own lives." The idea is no necessarily to learn to memorize enormous amounts of information," says James Fozard, associate director of the National Institute on Aging. "Most of us don’t need that kind of skill. Such specific training is of less interest than being able to maintain mental alertness." Fozard and others say they challenge their brains with different mental skills, both because they enjoy them and because they are sure that their range of activities will help the way their brains work.
Gene Cohen, acting director of the same institute, suggests that people in their old age should engage in mental and physical activities individually as well as in groups. Cohen says that we are frequently advised to keep physically active as we age, but older people need to keep mentally active as well. Those who do are more likely to maintain their intellectual abilities and to be generally happier and better adjusted." The point is, you need to do both," Cohen says, "Intellectual activity actually influences brain-cell health and size.\
What is the passage mainly about

Although they have voracious appetites, eating day and night, sea cucumbers have the capacity to become quiescent and live at a low metabolic rate-feeding sparingly or not at all for long periods, so that the marine organisms that provide their food have a chance to multiply. If it were not for this faculty, they would devour all the food available in a short time and would probably starve themselves out of existence.
But the most spectacular thing about the sea cucumber is the way it defends itself. Its major enemies are fish and crabs, when attacked, it squirts all its internal organs into water. It also casts off attached structures such as tentacles. The sea cucumber will eviscerate and regenerate itself if it is attacked or even touched l it will do the same if the surrounding water temperature is too high or if the water becomes too polluted.

As I sit at my desk and observe the frenzied play of these children who are working so hard at being children, I see a small boy to my right. What catches my eye is that he is standing in the area of the soccer goal, by himself, looking down at his shoes. He picks at his navy blue sweat jacket, pulling the string ties back and forth through the casing. He stubs his Nike’d tennis shoe in the dirt, again, and again, and again. I see his lips move--he seems to be talking to himself, all alone, oblivious to the world around him. There are children at play in the background, plenty to team up with, yet he stands idle, off to himself.
Watching him, I begin to fantasize about his melancholy. Is he an only child of working parents who are so busy with their own lives they don’t have time for him Or is he one of several children, caught in the stampede of family life, getting trampled on by the older children as they pass him up, and pulled down by the younger siblings as they compete with him. Is he loved or abused Smart or slow to learn What does he think about when he’s by himself What are his dreams His fears Is he a new child, too shy to make friends Or is he a victim of the cruelties of child’s play
Days of my own childhood come flooding back to me. Remembering the days when I felt as he must be feeling now, so alone. As an adult, I can still feel that sometime hollowness. I understand these feelings even less than I did when I was his age. I ache for this small child that bas so much to learn and experience, as much potential for pain in his future as happiness. I want to reach out to him, wrap my arms around him and tell him that it’s ok, he’s not alone, that I care, as will so many others in his life to come. I want to assure him that it’s alright to feel the way he does, but that it gets better and he must look to the good things, to learn from his experiences. I want to give him all the answers to all the questions that no one ever gets until they don’t need to know anymore.
I find myself rising from behind my desk, mesmerized by the little form before me. I walk towards the window, my eyes not budging front their goal. He’s still plowing the earth with the toe of his shoe, talking away to whatever has a moment to listen. My eyes fill with tears--I can’t bear this pain any more. I reach out for the window frame, leaning into it in weariness of a life hard fought, knowing of the battle he has yet to face...