Lehrstuhl für Neurobiologie und Genetik
Lehrstuhl Genetik + Neurobiologie, Biozentrum, Am Hubland, 97074 Würzburg
Url: http://bitte ergänzen
Research foci (and basic equipment-based research projects):
GENES, BRAIN AND BEHAVIOR
Martin Heisenberg, Lehrstuhl für Genetik und Neurobiologie
Biozentrum, Am Hubland, D-97074 Würzburg, Germany
Neurobiology is still young. It grows vigorously, it attracts students from all fields of science: it provides fascinating oppor- tunities for basic and applied research. Developmental biologists are beginning to tackle the tantalizing question of how the millions of neurons in the brain find their correct targets. New techniques nourish the old dream of the neuroscope, an instrument visualizing all the processes in the brain at any desirable detail. The field attracts more and more public attention. The brain, we are told by the mass media, may be the last frontier where the boundaries of scientific knowledge are not yet in sight.
Despite the glamour of youth, complacency would be unwarranted. If the main goal in Neurobiology is to understand the brain, progress is slow. How does a brain work? Nobody should miss the excitement and disregard the importance, of the many new discoveries published in hundreds of journals every week and month, but how much do they further our understanding of the brain? As was pre-Kepplerian astronomy, we are faced on the one hand with an abundance of data which by far surpass the capacity of any individual scientist`s mind, and on the other by a seemingly self-evident model of the brain which is not suited to incorporate all the detail, except at the expense of ever in creasing complexity. What is needed in the brain sciences is a unifying conceptual framework, a new basic model of the brain.
The activities of the Lehrstuhl für Genetik und Neurobiologie are devoted to this problem. The motto "Genes, Brain and Behavior" proposes to reflect upon what, at all, may be known of the functions of brains. In the motto, "Brain" is flanked by "Genes" on one side and by "Behavior" on the other. Both aspects are crucial for a conceptual framework and both tell us a lot of what one can know about brains and what not. Take the genes. Their products, the proteins constitute the basic units of neurobiological functions. In the last 25 years, with the advent of recombinant DNA techniques, we have witnessed the discovery of the biochemical diversity of brains. Today some 20 000 different proteins are thought to act and interact in the brain of an insect and, probably more than 50 000 in that of a mammal. We must give up alI hope to understand a brain by restricting our curiosity to the network level. Genetics has not only revealed this molecular complexity, it also provides the means to exploit it.
Genes are equally important with respect to the old question of homology. All brains, including our own, serve similar needs. They operate on similar principles and must have the same basic functional organization. However, at the morphological level this similarity is by no means obvious. Generations of biologists have battled about the homology of certain organs, tissues or cells in distantly related species and more often than not have failed to reach an agreement. This is different at the level of the genes. Most vertebrate genes have their homologues in insects and worms and, what puts an end to alI quarrels. the degree of relatedness can easily be quantified. On this basis the common functional organization of brains can now be worked out.
What molecular genetic analysis does not reveal is the special status of the human brain. Protein kinase A of the gorilla for instance, is just as good a kinase as that of Homo sapiens. This is not to say that the last 10 million years, the species-specific part of our evolutionary history could be ignored. No, but it occurred as the modification of a preexisting network of genetic functions, subtle and distributed. The human genome may differ from that of the gorilla by only 1 % but these mutational events are spread out evenly over nearly alI genes. Thus, the specific genetic properties of our species which enable us, for instance, to learn a human language, to develope a cuIture and to have consciousness, may, to a large extent, not be interpretable at the molecular level.
This point reminds us of a fundamental limitation in the brain sciences: The list of functions of a protein may not be complete. We can never fully account for them. They have been shaped in a long evolutionary process which can not be reconstructed. Functional studies of biological systems are necessarily open-ended. This is important since no function is self-evident. One has to be aware of it before one can ask whether it occurs. In many present-day functional problems in the brain sciences the functions are obvious enough that this limitation may be of little concern. But we should remember it whenever we apply biological concepts to the individual human brain. We are all full of brain functions which govern our hopes, fears, achievements and failures. We hide them deep in our subconscience and take great care that not even we ourselves are aware of them.
With this remark our little discussion has already shifted from genetics to behavior, from the newest to the oldest approach in the study of brain function. To modify a famous quotation from Th. Dobzhansky: "Nothing makes sense in the Neurosciences except in the light of behavior." Behavior is the main function of brains. While the influence of sedentary organisms on their environment is slow and gradual, ambulatory organisms change their environment quickly and radically. Their brain increases the benefits they draw from this "manipulative" property. Brains arose in evolution by natural selection on behavior. Already early in the century, the Behaviorist school of psychology has stressed this point.
The common functional organization of brains, as mentioned above, must be described in behavioral terms and can only be verified by behavioral experiments. The challenge for the behavioral scientist is to reveal and to describe, in these terms, the relevant brain processes which lie behind the level of the overt behavior. This basic scheme of brain function, if it can be conceived, will apply to small and large brains alike since it will relate to the general living conditions of all animals and man. It may, therefore, help to finally bridge the gap between biology and psychology.