The neurobiologists from the University of Amsterdam carried out their observations on the hippocampus of rats. The hippocampus probably plays an important role in converting the short-term memory to the long-term memory.
The hippocampus contains two sorts of brain cells: pyramidal cells and interneurons. Pyramidal cells are the most important cells in the hippocampus. They process incoming information and pass on information to pyramidal cells in other areas of the brain. The interneurons can control the activity of the pyramidal cells.
The researchers studied the electrical signals that nerve cells use to communicate. They found that the interneurons inhibit the pyramidal cells in two ways. Some interneurons receive the same signals as pyramidal cells and so they can control what information the pyramidal cells received. This is therefore a form of prior control. Other interneurons can only control the pyramidal cells when these want to issue new signals. They control the activity of the pyramidal cells retrospectively.
One advantage of the double control mechanism is that the brain can be continually alert without becoming overloaded. Epilepsy illustrates the importance of not being overloaded. During an epileptic seizure, the brain (including the hippocampus) becomes disorganised and all of the pyramidal cells fire signals at the same time. The brain becomes overloaded and can no longer respond adequately to external signals. The patient then becomes unconscious.
There are indications that the interneurons in epilepsy patients are affected, with the result that the pyramidal cells are less well controlled. Future research needs to establish which of the two types of interneurons is affected.
The defence of the doctoral thesis will take place on 18 January 2002. Ms Wierenga's supervisor is Prof. W.J. Wadman.
The research was funded by the Netherlands Organisation for Scientific Research (NWO).