Learning requires rhythmical activity of neurons

When we learn and recall something, we have to concentrate on the relevant information and experience it again and again. Electrophysiological experiments in mice now show why this is the case. Scientists belonging to Matthias Eder´s Research Group measured the transmission of electrical impulses between neurons in the mouse hippocampus. Under the fluorescence microscope, they were able to observe in real time how the neurons forward signals.

Jens Stepan, a junior scientist at the Max Planck Institute of Psychiatry in Munich, stimulated the input region of the hippocampus the first time that specifically theta-frequency stimulations produce an effective impulse transmission across the hippocampal CA3/CA1 region. This finding is very important, as it is known from previous studies that theta-rhythmical neuronal activity in the entorhinal cortex always occurs when new information is taken up in a focused manner. With this finding, the researchers demonstrate that the hippocampus highly selectively reacts to the entorhinal signals. Obviously, it can distinguish important and, thus, potentially recollection-worth information from unimportant one and process it in a physiologically specific manner.

Filmstrip of an activity wave through the hippocampus. The activity wave is triggered by stimulating the input region with a microelectrode (black arrow) and recorded using voltage-sensitive dyes. Warmer colors represent stronger neuronal activity. Credit: MPI of Psychiatry

With this study, Matthias Eder and colleagues succeeded in closing a knowledge gap. "Our investigation on neuronal communication via the hippocampal trisynaptic circuit provides us with a new understanding of learning in the living organism. We are the first to show that long-term potentiation depends on the frequency and persistency of incoming sensory signals in the hippocampus," says Matthias Eder.

More information: Jens Stepan, Julien Dine, Thomas Fenzl, Stephanie A. Polta, Gregor von Wolff, Carsten T. Wotjak and Matthias Eder (2012) Entorhinal theta-frequency input to the dentate gyrus trisynaptically evokes hippocampal CA1 LTP, Frontiers in Neural Circuits, Volume 6, Article 64, 1-13.

Provided by Max Planck Society