Is Our Nervous System Beginning to Understand Itself?
Is it possible to describe developments going many million years back?
We'll try just that in this essay.
First, we're describing basal similarities in the function of the nervous system.
Then we'll look at biological differences developed through evolution.
Many authors have detailed the structures of our peripheral nervous system and our brain.
However, if you ask them how the structures of the brain cooperate, their explanations become vague.
We have for a long time been missing an account of our nervous system as seen from a simple biological viewpoint.
Leif Rasmussen, Professor emer.
Jesper Dybvad Olesen, C.Sc.
October 2018
© Copyright Mentorsclassroom.com
Table of contents
Insights
1. Similarities and Model Systems in Biology
2. Examples of the Use of Model Systems
3. Features Connected with our Consciousness
4. Free Will
Overview After Insights
Insights
It is our luck in presenting this essay that certain basic principles in the function of the nervous system go far back in time. Furthermore, many structural and molecular similarities have been retained in the course of the biological evolution.
Changes in Environment and Biological Adaptations
It is a problem with our present brain that it has been adapted to living conditions of past times. These conditions have changed ever since the first vertebrates appeared. Let us jump fast forward from the society of 'Hunters and Gatherers' through thousands of generations to modern times. Every step in evolution has presented our nervous system with new tasks. The brain's development has often (always?) lagged behind the actual requirements.
Theodor Dobzhansky, a leading figure in the study of evolution, has coined an important phrase in biology: "Nothing in biology makes sense except in the light of evolution" [1]. That means that all biological structures and functions – at any time in history – were the best ones that could be obtained under the prevailing circumstances. Any textbook on biology – and medicine – should include this quotation by Dobzhansky at the beginning and end of the textbook.
Heresy and Conformity
Our nervous system is complex; our brain consists of 100 billion nerve cells, each with many and changing connections. Some people have called it the most complicated structure in the Universe. Maybe they are right.
Civilizations have been advanced by people who have disagreed with previously accepted knowledge. Recently, such people have developed – right or wrong – scientifically based ideas about as fields as varied as: far-away times; the large Universe; the smallest parts of matter etc. However, other people just accept the surroundings as they appear. This balancing act between the desires for 'heresy' and for 'conformity' has always taken place. Development has been fastest when humans have been challenged.
1. Similarities and Model Systems in Biology
In Zoology we have traditionally studied the kind of differences anybody could see. However, during the latter decades we have also seen emphasis put on similarities and patterns in biology. Slowly we have understood that physiological, biochemical and genetic similarities made it easier – and legitimate – to study interesting functions in any animal or any cell presenting advantages with respect to cultivation or manipulation. A good example is the use of mice and rats as experimental animals. Today, we also use bacteria, uni-cellular animals and plants as models for activity in human cells.
Common Biological Control Mechanisms
The study of cellular similarities gave us important results. Imagine for a moment a common basic plan for all life on Earth. If correct, the old mechanisms in control of a fundamental feature like the cell cycle would also be common in today's cells. Such mechanisms were first found in cells from mammals. Therefore there was an animosity towards accepting the idea that these mechanisms could have originated much earlier – in our uni-cellular ancestors. Possibly this history reflects that physiologists, biochemists and geneticists had no knowledge of the field of evolution. Biology bloomed when results from uni-cellular and other 'simple' model organisms could be used in technology and medicine.
2. Examples of Use of Model Systems
Paramecium's Avoidance Reaction
The uni-cellular animal, Paramecium, shows an avoidance reaction [2]. The animal moves forward in the water propelled by beating of its cilia, long 'hairs'. If it meets a hindrance Paramecium has a fixed pattern of response: it will reverse, tumble, and then swim forward in another direction than that in which it arrived. It looks like a well-considered chain of events.
The beating direction of the cilia is controlled by the concentration of calcium-ions near the base of the cilium. The contact between the cell and an object will open calcium channels on the surface of the animal and increased Ca++ concentrations make the cilia beat reverse. In a short time the excess Ca++ is reduced again, and the cell moves forward – in a slightly different direction than before. Some mutant cells of Paramecium are lacking the avoidance reaction. They are missing the ion channels mentioned above. This shows that the cell reaction is 'automatic'. The cell has not considered what is effective for it – although it looks like that. The anatomy of the cilia in combination with a control of the internal concentration of Ca++ explains it all.
There are similarities between Paramecium and ourselves. We have many cilia exactly like Paramecium's in our body. Because they are fixed onto stationary cells, the cilia beating moves both surrounding fluids and particles located on the cell surface away. In a non-smoker's trachea there are about 10 million beating cilia per square millimeter – moving fluids up and away from the lungs. All these cilia react to changes in concentrations in Ca++ as described in Paramecium. In addition, many of the signal systems in our cells react to movement of Ca++ across the cell membranes.
From Snails to Nobel Prize
Many researchers have studied the function of the nervous system. In the year 2000, a Nobel Prize was given to Carlsson, Greengard and Kandel for their studies on transmission of cellular signals in nerves. Kandel and colleagues used a snail in the study of its reflexes. This snail has only few nerve cells and they are so large that they can be seen without a microscope. Kandel et al. consolidated their results obtained on snails with responses in mammalian nerve cells.
Below we present a short view of the present idea of our knowledge of our nervous system. The historical development has taken place during the last hundred years – with increasing intensity.
The Headless Frog
Professor Brandt Rehberg showed experiments on reflexes in a frog at the Zoophysiological Laboratory at the University of Copenhagen, Denmark [3]. The frog's head had been removed half-an-hour earlier. During the first 30 minutes after decapitation the activities in the spine of the headless frog are so chaotic that it is not possible to carry out the experiment.
The 'frog' was fastened to a stand and a powerful lamp cast a shadow picture on the wall, making it possible for 500 people in the audience to see what happened: Rehberg put a small piece of filter paper dipped in acid on the skin on the right side of the dead frog. A moment later the right hind-leg removed the paper. Then he returned the paper, now holding the right leg between his fingers. The frog hesitated but removed the paper with its free, left hind-leg. They were all reflexes in a frog that had been dead for 45 minutes. These reflexes ran a characteristic course: sensory cells in the skin were stimulated and the signals were converted in nerve cells of the spine to contractions in the muscles of the hind-legs, resulting in the removal of the annoying paper.
These results fit the idea that reflexes are basal functions of the nervous system. Reflexes are stereotype, but may be quite complicated. Furthermore, even if only a tiny fraction of our brain cells also becomes involved, the end-result may be very complex. Maybe our dreams indicate that brain activity can appear without sensory cells being involved [4]. This problem has not been solved yet.
Our brain always receives many signals from the outside. It decides in unknown ways whether these signals should be reacted on or not. Our consciousness – which we don't understand – developed maybe in connection with the growth of the brain in relation to the size of our body.
It has been proposed that the present size of our brain arose after we began controlling fire for cooking of our food [5]. Such food is utilized faster and better than raw food, and that provided time for other activities than just always eating – the way apes and monkeys are doing. Our brain weighs just a few per cent of our body, but it is utilizing one-fifth of our total energy. Even during sleep the brain is very active.
3. Features Connected with our Consciousness
Our nervous system has many inborn patterns and reflexes. Patterns in babies fit in a wonderful way into the patterns of their mothers. Without a close fit between the two, mankind would not have survived.
Two-year Old Babies and Their Recognition of Faces
Eric Kandel presents an example of that with root in the biological evolution [6]. He says that two-year children can distinguish between more than 1,000 faces. This happens in spite of the fact that a face has only few features: two eyes, a nose, and a mouth, all on an oval background. It doesn't sound probable that this ability has been learnt. So, we are dealing with inborn patterns.
This ability is important for children's recognition of their mothers' face. It has been a central part of our development. Similar accounts – in slightly different shapes – are known from many species, especially from birds and mammals, taking care of their offspring.
Tabula rasa
Some people think that humans are born with a tabula rasa, 'a pure slate', and that all knowledge stems from experiences. We'll emphasize that in biological terms we know little of this consciousness. Anyway, we can hardly maintain the idea of a tabula rasa: we know that even newborns have many reflexes without which they wouldn't survive for long. Today, most people would probably think that even the personality to a large extent is inborn, although it may not show up until a late time point in life.
Human Memory
No nerve cells touch each other; they are all connected only by transmitter compounds in synapses. In this way the nervous system retains its plasticity. We have at least two kinds of memories: the short-term memory that is lasting maximally a few minutes. This short-term memory makes it possible to make plans and to read sentences, where you have to remember the beginning before you get to the end. This type of memory may be unique for mankind.
The long-term memory is different. One theory says: when several nerve cells are active at the same time and the concentration of transmitter compounds remains high, these compounds may reach the cell nucleus. Then proteins, called 'transcription factors', become activated and 'loosen' other proteins that are keeping the tightly bound DNA inactive. In this way new RNA and proteins are formed and new synapses appear. These synapses may exist during a life time. Age-dependent changes may lead to a reduction in these events – causing a gradual loss of ability to learn.
Researchers have subdivided our memory into many subgroups. We expect that future research will present us for many more details than we see today. The foundation of our present concepts is to a large extent due to Eric Kandel.
In Artificial Intelligence, AI, or Machine Learning, the quest for the Holy Grail has consisted in constructing an algorithm that can simulate our brain. Long time ago it was thought that when we got enough capacity of memory the problem would be solved. In the year 2018 we have computer memories so large that they correspond to more or less the collected information our brain receives during a long life. People in Machine Learning are now realizing that never the less we are not near the goal of constructing algorithms capable of handling information: register, catalogue, sort, create, moralise (?) etc. the way our brain is doing.
4. Free Will
There are many definitions of 'free will'. One goes like this: a free will is the possibility that a person could have reacted in another way. Another argues that common sense controls the actions of a person – independent of natural or supernatural factors. Whenever we agree on a definition of 'free will' several other questions arise: how often does a given person exercise his free will? Will the same person's free will result in the same reaction every time? Can a person's free will result in indecisions with respect to various issues?
Some choices are unimportant – tea or coffee, other choices are important, and in other cases you are not able to choose freely because you are born into a system of un-breakable rules. So far, the question of free will seems to lack an explicit meaning. In spite of that, certain groups of people have their (fixed) ideas of other people's free will.
Thus the starting point for judges is that we all have a free will. A judge will focus on the Law – without any other evidence than interpretations of the text of the law, and statements from witnesses. In case of insanity at the moment of the deed, the judge may decide: "Guilty, but exempt from punishment". Here is another case for believing in the free will: the Church in Middle Ages maintained the idea of an All-knowing and Loving God. In that case the Church also had to postulate a free will otherwise the thought of a good God combined with Hell becomes meaningless. Probably, today this opinion is still prevailing among theologicians.
What we are missing is a commonly accepted definition of a 'free will'. When we have that we can establish experiments whose results can tell us if our definition is true or false. A third possibility is that the question will remain unsolved – at least for some time.
Overview After Insights
We have mentioned features of the development of our nervous system through times. Brains have always changed in such a way that those which were best adapted to the environment had a greater chance of surviving than those less adapted. Each species has had its own challenges and the results have varied with the challenges. In general, Nature has preserved many basal principles through time.
Using biological model systems we have got insight into some of these basal features: Movement of ions across cell membranes and their effects; sensory inputs leading to contraction of muscles; and recognition of patterns in the youngsters of mammals. We have mentioned a hypothesis, that will explain that the development of our brain depended on our ancestors' use of fire for preparing food.
We have mentioned a couple of memory types in which some of the biochemical features are known; we have touched on the concept of 'free wills' for making decisions – a riddle not yet solved.
In spite of large holes in our knowledge of the function of our brains we attempt to present a coherent story about it. This story has its origin in biological evolution. "Nothing in biology makes sense except in the light of evolution." The future may show which details have to be revised. Anybody may see differences in the World – and also similarities are interesting.
References
1. Theodosius Dobzhansky, 1973. Variations on the theme of variation. "Nothing in Biology Makes Sense Except in the Light of Evolution". nekhbet.com/dobzhansky.shtml
2. Herbert Spencer Jennings, 1904. The Behaviour of Paramecium. Additional feature and general relations. J. Comp. Neurol. 14, p. 441- 510.
3. August Krogh og Poul Brandt Rehberg, 1953. Menneskets Fysiologi, Forsøg 53, p. 98, 12. udgave, Gyldendalske Boghandel, and personal recollections by Leif Rasmussen.
4. Michael Finkel, 2018. Want to fall asleep? Read this story. National Geographic, August, 48-77.
5. Rachael Moeller Gorman, 2008. Cooking up bigger brains. Scientific American, 298, p. 86-87.
6. Eric Kandel, 2016. TEDxMet, Oct. 28.