The Chemistry of Learning

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 Hyden, 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. Hyden 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, Hyden 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.

Nonsense Protein? Increasingly, researchers at the conference tended to make a sharp distinction between long-and short-term memory--in other words, the difference between a man's ability to remember a poem learned in grammar school and his inability, for the life of him, to remember the name of the fellow he met at lunch yesterday. Sweden's Dr. Hyden felt that the creation of protein (as in pigeons, rats and goldfish) is essential to man's formation of long-term memories. Human brain cells, said Hyden, seldom divide and replace themselves as do most other cells in the body. The neurons that a child has at six years must last him a lifetime. As he ages, some of them become damaged or die, so the brain's output of RNA in learning situations is decreased.

The brain's RNA and protein production are originally determined by deoxyribonucleic acid (the DNA of Biochemist James Watson's bestselling The Double Helix) that is established in the embryo by the sex cells at the time of conception. There is evidence, said Hyden, that the DNA in an old animal differs from that in a young one--and the same is true, presumably, in man. Here, Hyden opened the door a chink for a glimpse into an admittedly farout future. If a reasonably pure extract of brain DNA is injected into some animals, he said, their protein synthesis doubles within an hour. But he was careful to insist: "This does not mean that an elixir of life has been found." Hard facts remaining to be determined, he said, are whether this is a "functionally valuable or a nonsense protein," and whether the effect will last for days, hours or years.

*Named for the doctor who accidentally helped to open the door to research in brain chemistry in 1928 by discovering that overdoses of insulin can drastically alter the course of some mental illnesses.

This file is automatically generated by a robot program, so reader's discretion is required.