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Recharging your batteries Frank Haas in conversation with neuroscientist Gerd Kempermann about getting old and staying new ILLUSTRATIONS Shiwen Sven Wang
For the moderately educated layperson, the brain is a very complex matter. What’s it like for you as a professional? Considering everything you have learned, has it become even more complicated or are you resolving its many mysteries? A bit of both. The more you know, the more questions you have, of course. And in the sciences you soon find out that, for some things, there are no answers – yet for others there are clear explanations. You may have the occasional victory along the way, when you discover something that had previously been misunderstood. All in all, however, the brain is incredibly complex, and, when it comes to understanding it, we are still really scratching at the surface. But that’s what makes it so fascinating. The aging of the brain is your main field of research, and you focus on an area called the hippocampus. And this hippocampus is flexible? Not just flexible. More like plastic and malleable as well. Unlike a computer, a brain undergoes constant reconstruction. And if this process grinds to a halt, then the brain as a whole stops working too. Interestingly, there is one region of the brain that is also known as the “gateway to memory.” That is the hippocampus you referred to, and it is particularly malleable. All the information we receive and absorb has to be processed there if we want to store it. And what distinguishes this central region of the brain is the fact that it produces new nerve cells throughout life. These new nerve cells are called neurons, and the process is known as neurogenesis. The rest of the brain lacks this ability, which is why degenerative diseases are such a problem: nothing grows back. You can donate blood and soon you will have your full complement again. Or you might go to the hairdresser’s once a month because your hair keeps growing back. The skin’s stem cells continuously regenerate. The intestine is another organ that constantly renews its cells. The brain doesn’t do that, with this one exception. The renewal in the hippocampus is not the replacement of something lost, though. Instead it’s a continuous
process that never stops adapting its network of neurons in this region until the day we die. How exactly can I best visualize this? In concrete terms, which functions can I acquire or extend? The hippocampus is the place where information is filtered, where it is processed, compressed, and structured chronologically in a way that allows us to adjust flexibly to our environment and our experiences. That’s a very special feature of the human brain: it helps us adapt well to changing circumstances. The human race is able to colonize the whole planet, from areas at the poles with sub-zero temperatures to scorching hot regions, because we possess a high level of cognitive flexibility. As our geographical range increases, so do the cognitive challenges entailed. The more we move around, the more we have to remember – about what is happening currently and which information we have received. And we need to be able to organize this information by its time. This is called episodic memory. The hippocampus is also responsible for this function. For example, in order to find our way back to a place we’ve been, we need to replay the turns and directions we have taken backwards. In other words, we need to keep things in order. Storing memories in a chronological sequence is extremely important for humans because it lays the foundations for our autobiographical memory, without which we could not conceive of ourselves as people at all. To a very large extent, we are composites of our pasts, and we depend on our ability to remember to be ourselves. It’s horrible to see dementia patients losing track of their own biographies. They do not lose their dignity or status as human beings, but they lose sight of themselves as human beings. We have now discovered that it is these regenerating neurons that make flexible adjustments possible, enabling us to distinguish between what is old and new, even when there may be very little difference in time between them. If you leave your car in a large parking lot every day, but not necessarily in the same spot, you always have to remember where it is.
