Cemented Memory
The better we learn something, the more hands the nerve cells in the brain shake and the tighter they hold each other. It has finally been shown directly that learning actually works according to this principle. How is the information memorized? Quite simply: In the brain, the nerve cells involved connect more firmly to one another by strengthening the connections between the neurons, the synapses, through so-called long-term potentiation. The phenomenon of long-term potentiation was discovered more than thirty years ago - however, it has still not been clearly proven that it is really a consequence of learning. Now, finally, two independent working groups have succeeded in testing and counter-testing this theory.
Jonathan Whitlock of the Howard Hughes Medical Institute and his team tackled the learning process problem from the beginning: he tested whether a learning process actually induces long-term potentiation [1]. To do this, he implanted fine electrodes in the hippocampus of rats, the area of the brain in which the animals learn and store spatial information. He then taught the rodents to avoid an enticingly dark room, where the animals were given a mild electric shock.
We prove what everyone always believed
(Mark Bear) When the scientists then compared nerve activity in the hippocampus before and after exercise, some of the electrodes showed a long-term potentiation after exercise. It was obviously a consequence of the learning process. Additional biochemical studies confirmed that learning was indeed what caused long-term potentiation."We're proving what everyone always believed," says a happy colleague, Mark Bear. Since the changes were only seen in some of the implanted electrodes, only individual nerve cells are apparently involved in this learning process.
Eva Pastalkova's team from the State University of New York rolled up the problem from the back: The working group assumed that what had been learned would be lost if long-term potentiation was deliberately prevented [2]. So far, this has not been feasible, since there was no substance that could have removed an already existing long-term potentiation like an eraser. Pastalkova now used a new substance called ZIP, which inhibits a protein that is necessary for the permanent establishment of long-term potentiation.
Her team also taught rats to avoid a certain place. The animals were placed on a rotating platform that was mostly safe, but where a mild electric shock could be administered in a designated stationary sector. When the power was off, the animals moved all over the platform. However, when the shock function was turned on, the animals learned very quickly to avoid the uncomfortable area as the rotating disc carried them there, and they remembered the dangerous spot for at least a day.
When the rodents had now learned their task, the scientists injected ZIP into their hippocampus 22 hours after the learning process. The animals promptly acted completely clueless and – just like before their training – let themselves be carried without resistance by the rotating plate into the danger zone: they had forgotten what they had learned. Even after a week, when the substance had long since disappeared from the animals' bodies, the ZIP-treated rats had no memory of the danger zone.
Comparative animals injected with a saline solution in the brain, on the other hand, knew exactly where it was going to get uncomfortable after the injection and continued to avoid the dangerous area. By removing the protein necessary to establish long-term potentiation, ZIP had successfully erased this and thus permanently erased the memory of the animals.
The experiments of the two working groups taken together thus confirm - each from a different perspective on the process of consolidation of what has been learned in the brain - the common view that learning strengthens the connections between the affected nerves and thus cements the memories.
