If a brain is exercised properly, anyone can grow intelligence

Here is a long, evocative, and ancient-style interpretation of the quote you requested:

The Eternal Flame of the Mind

There is a truth older than the mountains and as constant as the rising sun: the mind, like the body, grows only through use. The great Michael Merzenich, sage of our age, spoke this truth anew when he declared that “If a brain is exercised properly, anyone can grow intelligence, at any age, and potentially by a lot. Or you can just let your brain idle — and watch it slowly, inexorably, go to seed like a sedentary body.” These words, though born of modern science, carry the spirit of ancient wisdom. They remind us that the mind is not a vessel to be filled, but a muscle to be trained, a fire to be kindled.

Long ago, the philosophers of Greece and the mystics of the East understood this same principle. They spoke of mental discipline and spiritual awakening through continual striving. To cease that striving is to surrender to decay. For just as a sword left untended will rust, so too will an idle mind corrode in silence. The body at rest grows soft and heavy, and the spirit that ceases to seek wisdom becomes clouded, dull, and frail. The brain, Merzenich teaches, is not fixed like stone—it is living clay, shaped by every thought, molded by every challenge, strengthened by every act of learning.

Consider the tale of Socrates, who even in his old age, questioned, reasoned, and examined the world around him. He saw ignorance not as an insult, but as a beginning—a door to be opened by inquiry. He trained his mind through dialogue and doubt, sharpening it as a blacksmith tempers steel with fire. Or recall Leonardo da Vinci, who in his sixties dissected cadavers to understand anatomy, sketched machines that prefigured flight, and filled notebooks with curiosity that knew no end. These men lived proof that intelligence is not given, but grown. Their relentless curiosity kept their minds ageless, though their bodies withered in time.

Yet how many among us let the fires die? How many sit in comfort, content to repeat old thoughts, their minds sinking like stones into stagnation? It begins subtly: a day without learning, a question unasked, a challenge avoided. The brain, starved of effort, grows dim. Neural pathways once alive with possibility begin to fade. The mind, that miraculous instrument capable of reshaping itself, atrophies through neglect. This is the tragedy Merzenich warns of—the slow, inexorable decay of an unexercised intellect.

But there is hope, radiant and near at hand. For just as the body, through motion, reclaims its strength, the brain can be reborn through effort. At any age—yes, even in the twilight years—new connections can form, new wisdom can dawn. Read deeply. Learn relentlessly. Wrestle with unfamiliar ideas. Challenge yourself with language, music, mathematics, art—these are the weights of the mind. Let struggle become your teacher, and confusion your forge. For every act of learning, every spark of curiosity, strengthens the unseen fibers of your intelligence.

Do not fear difficulty—it is the sacred fire that purifies thought. The mountain is steep, but each step carves new strength. When you teach your mind to work, it rewards you with clarity, resilience, and wonder. The one who labors to understand becomes as the athlete of thought—nimble, enduring, ever-evolving. The one who refuses the labor becomes as the idle body, comfortable but dying by degrees.

So let this be your creed: Keep your mind alive. Feed it with challenge, nourish it with beauty, test it with truth. Speak not of age as a barrier, for the wise know that the brain never ceases to grow—it only awaits the command of will. Even as time bends your back, let your thoughts rise like morning light upon the world.

And when your days draw to a close, let none say your mind went to seed. Let them say you were alive to the very end—your thoughts bright, your curiosity fierce, your spirit young. For the brain, like a garden, blooms only when tended. Cultivate it well, and it shall bear the fruits of intelligence, wisdom, and eternal growth.