The brain
The human brain is the most complicated organ that nature has ever created: 100 billion nerve cells and many more contact points between them provide our brain with capabilities that no supercomputer can match to this day. One of its most important characteristics is its ability to learn. But how can a collection of neurons learn anything in the first place? And can this ability be specifically improved?
Until a few years ago, scientists thought one thing was certain: an adult’s brain will not change. Today, however, we know that the brain is being constantly transformed right up until old age. Some neurobiologists even draw comparisons with a muscle which can be trained. Sellers of so-called brain jogging programmes are now picking up on this idea, offering exercises which are intended to increase learning and memory performance.
The idea that the brain remains capable of learning for a lifetime remains undisputed from a scientific viewpoint. If it were not, humans would not be able to overcome the wide range of challenges that we encounter during the course of our lives. For example, even in old age we can learn a foreign language and yoga, can remember the face and voice of a new work colleague, or the route to a new pizzeria.
However, many scientists doubt whether brain jogging exercises increase the general performance of the brain. They assume that the effects of the coaching have an impact only on the task which is being trained. According to this view, other capabilities accrue little or no benefit from brain jogging programmes.
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Synaptic plasticity
What happens exactly when our brain learns and stores something new?
Learning takes place at the synapses – those are the locations at which the electric signals are relayed from one nerve cell to another. Neuroscientists have discovered that synapses can vary the effectiveness of the transfer. This phenomenon is also described as synaptic plasticity. For example, a synapsis can also be strengthened by a procedure called long-term potentiation (LTP), in which the synapsis distributes more neurotransmitters or forms more neurotransmitter receptors. Similarly, the signal transmission at a synapsis can be reduced by long-term depression (LTD).
The transmission of signals can, however, not just be strengthened or weakened; it can also be enabled in the first place or completely stopped. For example, neuroscientists know today that synapses can be completely re-formed or dismantled, even in the adult brain. In a few places such as in the olfactory system, new nerve cells can be formed one’s entire life. It is therefore not an exaggeration to claim that our brain is a life-long construction site.
Consolidation and deterioration, building-up and reduction - the strength with which the signals are relayed between nerve cells is being constantly adjusted. A simplified way of looking at it is imagining that the transmission of signals is strengthened when the brain stores something – and is weakened when it forgets something. Many neuroscientists today share the view that the synaptic plasticity is the basis of learning and memory.
Without plasticity, the brain would be missing something fundamental: its ability to learn. Learning is much like sports: the more that a certain skill is needed, the more effective it is handled. If you drive a taxi, for example, you need to have a good sense of direction and remember routes. Your spatial memory will improve as a result of your work each day. This will leave behind traces in the brain, such as in the brain of London taxi drivers: researchers have found that the hippocampus in their brain – an area in the brain which is crucial for spatial memory – will become bigger over time. Clearly a spatial sense of direction being trained in such a way needs more space! It is still unknown whether taxi drivers generally have a better memory.
The plasticity also helps the brain to repair damage at least partially. If nerve cells die off in a stroke, neighbouring areas of the brain can partially take over the functions of the affected area. At the Max Planck Institute for Human Cognitive and Brain Sciences, researchers have found that the brain can in this way partially compensate for damage after a stroke. Scientists at a number of Max Planck Institutes are investigating how the brain and its nerve cells remain plastic.
Another important field of research lies in the connections of the brain. Each of the approx. 100 billion nerve cells in the human brain receives signals from other cells via tree-like structures – which are called dendrites – and offsets them against each other. In doing so, they form their own electric signal that the cell relays to another using a thread-like axon.