Rhythmic Learning: Our Oscillating Reality

Researchers at the Max Planck Institute of Psychiatry in Munich, have discovered an important mechanism for long term learning in the hippocampus of the mouse brain.

Max Planck Institute

The hippocampus represents an important brain structure for learning. Scientists at the Max Planck Institute of Psychiatry in Munich discovered how it filters electrical neuronal signals through an input and output control, thus regulating learning and memory processes. Accordingly, effective signal transmission needs so-called theta-frequency impulses of the cerebral cortex. With a frequency of three to eight hertz, these impulses generate waves of electrical activity that propagate through the hippocampus. Impulses of a different frequency evoke no transmission, or only a much weaker one. Moreover, signal transmission in other areas of the brain through long-term potentiation (LTP), which is essential for learning, occurs only when the activity waves take place for a certain while.

...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.

...One possible reaction is the formation of the so-called long-term potentiation (LTP) of signal transmission at CA3-CA1 synapses, which is often essential for learning and memory. The present study documents that this CA1-LTP occurs only when the activity waves through the hippocampus take place for a certain time. Translating this to our learning behavior, to commit for instance an image to memory, we should intently view it for a while, as only then we produce the activity waves described long enough to store the image in our brain. 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. _MedXPress_via_Max Planck

The translation from the German is a bit sloppy, but the basic idea is that in order for the brain to remember something, the information must be encoded properly and presented for a minimum time period.

We have looked at the importance of brain oscillations in consciousness and cognition, previously. Specifically, oscillations in the gamma band -- modulated by theta frequency oscillations -- appear to facilitate communication between different brain centres in an intermittently synchronous manner.

In other words, unlike digital computers, the brain does not have a central clock to maintain synchronous transfer of data. But by using specific modulated brain frequencies, the brain can apparently synchronise information transfer between different parts of the brain for short periods of time.

This is a key concept in understanding how sophisticated biological brains function. An incredible amount of insight can be derived from that simple concept, and Al Fin cognitivists anticipate that both neuroscience and the broader field of cognitive science will benefit immensely, once the insights are more broadly propagated within the various fields of study involved.