New insight into mechanisms of hippocampal rhythms

A research team from Berlin, Munich and Haifa has presented new findings concerning the function of the hippocampus, a region of the brain that is important for memory formation. The researchers investigated cellular mechanisms of high-frequency rhythms, which play a key role in memory processes, and possibly also in various brain disorders, albeit in a different manner.

In the current issue of the Neuron journal the research team of scientists in the NeuroCure Excellence Cluster at Charité - Universitätsmedizin Berlin, the Bernstein Centers in Berlin and Munich, and the University of Haifa, presents new findings concerning mechanisms of hippocampal rhythms. Within the scope of memory formation the hippocampus acts as a kind of intermediate memory for the brain. In rest phases, such as during sleep, information that was previously taken in is consolidated and passed on to other regions of the brain for final storage. This hippocampal function is linked to rhythms, so-called oscillations. These rhythms are very similar to the brain waves measured by a physician using an electroencephalograph. The development of these rhythms depends on organized interaction between a multitude of nerve cells. Research in recent years demonstrated that suppression - or intensification - of brain oscillations can impair or improve learning.

In their study the researchers are now concentrating on so-called ripple oscillation, a very fast rhythm at a frequency of 200 Hz, the mechanisms of which are still little understood. They investigated electrical currents in individual hippocampal cells that occur during ripple oscillation. "Our results show directly for the first time how excitatory and inhibitory impulses interact during ripples on a very fast timescale," reports Nikolaus Maier, a neuroscientist at Charité. Understanding these mechanisms is important, not only within the scope of memory research but also because any change in synchronous activity can have fatal consequences. "Disturbance of the hippocampal rhythms can be a potential cause of pathological conditions like epilepsy, schizophrenia or memory impairments in Alzheimer's disease," explains Dietmar Schmitz, coordinator of the NeuroCure Excellence Cluster. That is why the results now published also represent a basis for researching future approaches to clinical treatment.