Neurology: The Chemistry of Learning

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Man has been developing his brain for a million years or more, but only in the past seven years has research into its workings assumed significant dimensions. Last week in Manhattan, 70 of the world's leading experts on brain processes met at a New York Academy of Medicine symposium sponsored jointly by the Manfred Sakel Institute* and the Foundation for Research on the Nervous System. In sum, what the researchers had to say was that when brains work, the reaction is chemical —and complex.

Study in man is vastly complicated by the fact that the human brain contains an estimated 10 billion nerve cells called neurons, and another 100 billion of a second type called glial cells. The fluid bath in which they are suspended is an important element in their electrochemical interactions. Moreover, said Sweden's Dr. Holger Hydén, one big neuron may have on its surface as many as 10,000 points of contact (synaptic knobs) with other neurons (see chart). But by means of exquisitely delicate instrumentation and an electron microscope, Dr. Hydén has discovered that when human neurons are stimulated, some of the millions of ribonucleicacid (RNA) molecules inside them give orders to the glial cells to manufacture new proteins. The nature and pattern of these proteins contain an imprint of something that has been perceived, and may become a part of a memory.

Pecking Order. The reaction is more readily observable in animals, Hydén reported. When a normally lefthanded rat was forced to learn to use his right paw to get food out of a tube, cells in the most highly developed part of the brain (the cortex) produced a special kind of RNA as well as proteins. A similar thing happened in goldfish that were forced to learn a new kind of swimming by having buoyant plastic foam stuck under their chins by Dr. Victor Shashoua of M.I.T. Fish that Dr. Shashoua made work just as hard swimming against a current, but without learning anything new, did not produce extra RNA.

Dr. Samuel Bogoch of Boston's Foundation for Research on the Nervous System taught pigeons to peck a particular button to get a kernel of corn from a machine. He found that the chemical brain reaction was not only the creation of new brain protein, but protein-sugar combinations (mucoids) as well. Until three years ago, said Dr. Bogoch, only 20% of the brain's proteins had been identified. This has now been raised to 60%, and those known are divided into 16 groups. Two of these groups show a marked, though brief, increase when a pigeon learns his pecking order; the increase in a third group lasts longer—from three to eleven months. From his observations, Bogoch postulates that memory is encoded in the protein-sugar combinations. As indirect proof, he has found that drugs that prevent the formation of body sugars also impair the memories of trained animals.