If we take a young rat about 6 months old and put it into the water for a few minutes, then the locus of its movements on this first trial on the first day are given in the first row and column of figure 17: in this particular trial the rats legs didn't hit the stand beneath the water so the rat just swam around for a couple of minutes. But a few trials later, namely the fifth trial on this first day (see figure 17), the rat has learnt in the intermediate trials the position of the stand and so it swims immediately to it and sits down. Presumably this rat has formed a spatial memory of the position of the stand as a consequence of the normal functioning of its septo-hippocampal circuits. Of course by the fourth trial on the fifth day the rat has no trouble at all, no matter where it enters the water, it immediately locates where the stand is (see figure 17). on the fifth trial of the fifth day a nasty trick is carried out: the stand is removed and the rat is entering the water tank at a random position swims around frantically trying to find the stand; the locus of its movements are then centred on the position where the stand was, as shown in figure 17. We can use this technique to pick out those rats which are suffering senile dementia from those that are not. In the second row of figure 16 the results are shown for a three and a half year old rat, about the equivalent of a human at eighty: it is apparent that even by the fifth trial on the fourth day, after the rat had bumped into- the stand many times during the preceding days, it could still not locate the stand using spatial clues. This was an aged impaired rat, that is it had senile dementia. All old rats do not get senile dementia any more than all old humans do: in the fourth row of figure 17 the results are shown for another three and a half year old rat: by the fifth trial on the first day it had evidently formed a good spatial map of the whereabouts of the stand. On succeeding days it did as well as the young rat whose performance is shown in the first row.

Using this water tank technique, invented by Morris, we are able to sort out rats suffering from senile dementia from those that are not suffering from senile dementia. This is we can separate out those whose septo-hippocampal circuit is functioning from those in which these circuits are in bad shape. If we take an aged rat suffering from senile dementia now and operate on it in the way I previously described, that is introducing embryonic septal neurones into its hippocampus, then after a month r so has elapsed to allow the implanted neurones to make connections, the water tank test shows that the rat has recovered its ability to lay down spatial memories (see the last row in figure 17). This approach clearly demonstrates that transplants of neurones from embryonic material which allows the reconstitution of damaged or degenerating neuronal circuits involved in the formation of spatial memory.

In conclusion then I have been proposing that we are confronted in the 21st Century with what I regard as the third great area of mystery concerning natural knowledge. The first involved the discovery of quantum mechanics in 1926 by Schrodinger and Heisenberg. The second was to some extent begun by Schrodinger himself with his little book "What is Life", which attracted physicists of high quality into biology. One of these was Francis Crick who after codiscovering the structure of DNA in 1952 went on to delineate the concept of the genetic code in specific ways which Schrodinger had only dreamed of in his little book. This helped lay the foundations of molecular biology that has come to dominate a good deal of science in the latter part of the 20th century, illuminating our understanding of embryology in particular. The third challenge for us now is the human brain.

Figure 18. A human embryo at 5 weeks (15 mm. long) The hands are clearly visible with the just clearly delineated fingers. The heart, with liver below, can be seen between the hands; the diaphragm separates the heart and liver. Most striking, are the two halves of the cerebrum which can be seen through the transparent skin of the forehead above the developing eyes.

There are two questions that I have laid stress on which will dominate science in the 21st century. one of these is what are the actual workings of the brain that give rise to consciousness and how does this develop (figure 18) . We have seen that consciousness involved in visual phenomena requires the correct funptioning of parietal cortex and inferior temporal lobe. The second question that we have considered is whether our increased knowledge of the workings of the brain, particularly in relation to the search for the neuronal concomitants of consciousness, will provide us with insights into means of ameliorating various neuronal diseases. In particular those diseases which arise as a consequence of vascular stroke and as a consequence of schizophrenia, diseases which produce hallucinations and which completely distort our consciousness of reality. This essay has stressed one possible approach to the problem. This is through the introduction into the appropriate parts of the degenerating brain of neurotrophic factors that allow for the survival of specific classes of neurones. Alternatively a transplant of appropriate viable neurones may be made to replace degenerating ones. The next century offers us the possibility of understanding our own brains.

Acknowledgments

I am extremely grateful to my colleague, Dr. Bogdan Dreher, for his critical reading of the manuscript and his many helpful suggestions.

Further Reading

Crick, F. (1988) "What Mad Pursuit." Weidenfeld and Nicolson. London.

Judson, H.F. (1979) "The Eighth Day of Creation". Simon and Schuster. New York.

Moore, W. (1989) "Schrodinger". Cambridge University Press. Cambridge.

Schrodinger, E. (1944) "What is Life?" Cambridge University Press. Cambridge.