Physiological mechanisms
underlying the basic functions of the central nervous system

Study of Glia

Posted: December 4th, 2009 | Filed under: Memory | Tags: , , , , , , | No Comments »

The function of the brain, or the higher nervous activity, is linked with the activity of the nerve cells. This is universally recognized and beyond doubt. That is why an article published some years ago by the well-known American physiologist Robert Galambos caused a great deal of controversy. The scientist argued that perception of the outer world, the formation of conditioned reflexes, memory, all the main functions of the brain have nothing to do with the nerve cells, but are associated with the glia, the tiniest cells which surround the neuron bodies and fill the gaps between their processes.

Improbable ideas are not a rare occurrence in biology, but they are usually forgotten before they gain popularity. Galambos’ ideas became known even in the Soviet Union, which is traditionally concerned with research on the nervous system. At that time scientists were, however, not prepared to discuss the functions of the glia elements as they could not support their arguments with proven facts. Almost nothing was known about glia in spite of the fact that glia cells are much more numerous than nerve cells. It was previously thought that they only supported the neurons and provided them with all they need as the blood capillaries never come directly into contact with the nerve cells.

The idea advanced by Galambos seemed to be too groundless to last for long. It did, however, attract followers in different countries, including the Soviet Union. For example, certain Georgian physiologists have voiced the assumption that the role performed by the glia was much more important than that previously ascribed to it. Unlike Galambos, however, they do not ascribe to the glia the function of consciousness or memory, but claim that the glia elements ensure the function of closing the temporary connections when conditioned reflexes are set up.

For a long time now histologists have known that many endings of the nerve processes in the central nervous system are bare, that is they are not covered with a myelin sheath. Calculations show that the electric current coming from these bare nerve endings has to be dispersed and that they are bad transmitters of excitation to the adjacent fibres. The Georgian scientists surmised that the closure mechanism consists in (hat a previously bare nerve ending acquires a myelin sheath and becomes more active. The insulation is made up of giia cells whose processes entwine around the nerve fibre forming a multi-layer myelin sheath.

As yet, it is difficult to say whether these suggestions will prove correct as the study of glia is only just beginning. It is beyond doubt, however, that the investigations will result in a new approach to the physiological mechanisms underlying the basic functions of the central nervous system.

Conditioned-Reflex Theory of Memory

Posted: December 1st, 2009 | Filed under: Memory | Tags: , , , , , , , | No Comments »

According to the second theory of memory, the process of remembering involves the formation of a new system and the building of new links between the nerve cells. Can these potential nerve contacts last throughout man’s life? Can the fading of memory in old age (the ability to remember new events diminishes) be accounted for by the fact that the reserves of the nervous system are exhausted by that time? Mathematicians cannot throw any light on the subject. However, taking into consideration that any nerve cell receives several thousand nerve endings, it is very likely that the nerve network of human brain is capable of storing all the information required.

An argument in favour of this theory is that the nerve cells themselves have changed very little in the course of evolution. The biochemical processes occurring in the neurons of lower animals and man are very similar. Progress has mainly been made in the increase in the number of nerve cells and the improved organization of the nervous system.

Not everything that we know about memory at present corroborates this theory. If the larva of an insect, for example, of a flour beetle, is trained to turn only to the right when moving in a labyrinth, the adult beetle witl retain this habit. Hence, its memory has not been disturbed in spite of the fact that, when the larva changes into the pupa, its body structure changes, and all the nerve contacts and 90 per cent of nerve cells are destroyed. It remains a mystery how its memory is preserved.

At present it is difficult to say which of memory theories is correct. But, as to a conditioned-reflex memory, there is a unanimous opinion that temporary connections exist between the nerve centers, which retain recollections caused by a conditioned stimulus, and a command point governing the responses to it. However, this still leaves a lot to be explained. How this connection is formed is obscure. Some scientists claim that this bond is purely functional and merely transmits excitation more efficiently through certain synapses. Others consider that the formation of conditioned reflexes is accompanied by the appearance of new contacts between the neurons due either to the growth of their processes or of new synaptic formations on these processes.

Biochemical Theory of Memory

Posted: November 29th, 2009 | Filed under: Memory | Tags: , , , , , , | No Comments »

All existing theories on the memory fall into two categories. The first is the biochemical theory of memory, which suggests that the information in the brain is coded on molecules of ribonucieic acid (RNA), or on some other macromolecules. The first argument in favour of this theory is that biochemical coding allows practically unlimited amounts of information to be retained. The second argument, which is even more forcible, is that this method of storing information dates back to the very first moments of life and that Nature still employs it for handing on information from one generation to the next.

By this is meant the so-called genetic information, a set of very rigid rules and demands that defines what every individual belonging to a given species is to be like. This not only governs the appearance of an animal and the specific functions of its internal organs, but also determines the pattern of its behaviour. No one teaches ant lions how to build traps, lie in wait and catch their prey; no one shows the spider how to spin its web; the female cabbage white butterfly tells automatically males of its own species from other admirers. This innate knowledge with which the animal is endowed is as permanent as other features of its organism. It was not without reason that Wagner, a Russian zoologist, suggested classifying spiders according to their behaviour rather than tb their morphology, which is perhaps more sensible since some species are very similar in their appearance.

The pattern of behaviour in higher animals and even in man is partly inherited. Nobody teaches a newborn baby to suck; it is an innate reaction of its organism. There seem to be very many reactions of this sort, though relatively little is known about them.

Scientists were recently very surprised to find that newly hatched chicks, even those hatched from eggs laid by a hen which has never seen a bird of prey, can easily tell a predatory bird from a harmless one. When the newborn chicks were shown a moving silhouette of a flying kite (a small head drawn into the shoulders, large widely spread wings, a long, thin body and a tail), they were panic-stricken. If the silhouette was moved in the opposite direction, it looked like a duck or goose on the wing (the tail became a head on a long neck stretched forward, and the small head, a short tail), the chicks were now no longer afraid of it.

This means that the image of a predatory bird is imprinted on the mind of a tiny chick, and this information is inherited from its parents with the help of a biochemical code. If the inherited image is coded biochemically, why should an image resulting from actual experience not be coded in the same way? We have noted repeatedly that Nature seldom neglects good finds. Why should it act differently this time?

Problems Pertaining to Memory

Posted: November 29th, 2009 | Filed under: Memory | Tags: , , | No Comments »

Modern biology is faced with the tremendous task of solving the mystery of memory. This problem is being tackled by hundreds of scientists all over the world. At present, we know next to nothing of what memory is, and what parts of the brain are involved in storing our recollections and the vast amount of knowledge that we have collected bit by bit throughout our lives; above all, we need to find out how all this information is coded in the brain. In other words, scientists must find out what paper, ink and alphabet our brain makes use of to imprint on the mind the information it receives.

These are just a few of the numerous problems pertaining to the memory. It would, for instance, be useful to know how the information the brain needs is sorted, selected and extracted from the stores of our memory. There is every reason to suppose that the human brain firmly retains all the information acquired, and that it is only the imperfect mechanism of extraction which is responsible for the fact that we use only a negligible part of the knowledge stored.