Can think nerve cells

Thinking is not a monologue

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Effective communication in the brain is only possible when the sending units (red) and receiving stations (green) come together in the right proportions.
Effective communication in the brain is only possible when the sending units (red) and receiving stations (green) come together in the right proportions.
© Max Planck Institute for Neurobiology / Nägerl
© Max Planck Institute for Neurobiology / Nägerl

Communication is the be-all and end-all of the brain. As a master of data exchange, each of the roughly one hundred billion nerve cells in our brain is in contact with thousands of neighboring cells. At these contact points, the synapses, the neural information flows along a one-way street: from the upstream to the downstream cell. The brain can only cope with its complex tasks if nerve cells can exchange information via such contact points at the right time and in the right place.

It's no wonder, then, that one of the brain's great qualities is its immense adaptability. This is based on the variability of the synapses, which can be built up and dismantled again as required. For most neuroscientists it is clear that learning and memory are only possible through this flexible exchange of information.

The two sides of information transfer

When new synapses are established and dismantled, the receptor sides of the contact points, the thorns, play an active role. If more information has to be processed, a nerve cell sets up more receiving stations: New thorns grow towards neighboring cells, and new synapses can arise. If the flow of information decreases, the synapses disappear and the thorns can retract again. The second side of the synapse, the transmitter unit (also called bouton), has so far only been assigned a reactive role in the synapse design.

However, this assumption was wrong, as scientists from the Max Planck Institute for Neurobiology have now been able to show. For the first time they managed to observe not only the receiving end but also the transmitting stations over a longer period of time. To do this, they marked some nerve cells with a red fluorescent dye and colored the cells connected to them green. With the help of a high-resolution two-photon microscope, they were able to observe the changes on both sides of the synapse in fast motion.

It quickly became clear that the transmitter unit of a synapse plays a much more active role in its construction and dismantling than previously thought. If the flow of information that a nerve cell has to pass on decreases, many of the now superfluous transmitting stations are dismantled. In addition, the scientists were able to prove the thesis that the breakdown of thorns actually leads to the loss of synapses, since the new experimental approach allowed them to observe the "breaking apart" of the contacts between boutons and thorns directly on the microscope.

Brain remodeling unexpectedly complex

"It is also particularly exciting that the bottom line is that the number of broadcasting stations remained roughly the same," says Valentin Nägerl. Because although the number of synapses is reduced when there is a reduction in the flow of information, new transmission stations have been created elsewhere. Since only the nerve cells originally communicating with each other were color-coded, the scientists could not tell whether the new transmitters passed information on to nerve cells that had not previously been involved in communication.

"It could be that synapses to inhibitory nerve cells are created in this way, which further reduce the transmission of the weakened flow of information," says Nadine Becker, interpreting her results. The scientists now want to investigate whether this is the case with more extensive cell staining. One thing is certain, however: It is not just the recipient cell whose structural changes enable information to be processed. The sender cell also reacts actively to the current situation and thus plays an important role in our ability to learn things or to remember them.

Max Planck Society (2008)