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Spatial Memory: Place Cells Lie in Wait

Researchers discover cells to prepare early for their spatial memory task

Memories, places and actions are stored in our brain. But what determines for a certain task the contribution of specific nerve cells out of billions of cells? For a long time scientists debated whether the cell’s activation in a specific brain region during a particular case is random or not. Jèrôme Epsztein, Michael Brecht, and Albert K. Lee of the Bernstein Center Berlin and Humboldt-Universität zu Berlin now proved clearly that it is not randomness. On the example of spatial memory in rats they showed that later active cells differ early from their quiet neighbors. Their findings push the understanding of memory formation a major step forward.

If we move in an unknown environment, a neuronal map is created in our brain. Particularly well understood is the memory function in rats. Cells of the rat’s hippocampus ensure that an animal always knows its location. Each of these so-called “place cells” is particularly active when the rat is in a certain area, the cell “fires”. Thus, each site is coded by specific cells. However, in the corresponding region of the brain are also cells that do not fire, they are "silent". This activity pattern and the selection of active cells is very specific for a particular environment.

Using a sophisticated method Jèrôme Epsztein, Michael Brecht, and Albert K. Lee succeeded for the first time measuring the electrical properties within individual cells of the hippocampus, while the animals were freely moving. They studied the electrical base line and the current level from which individual cells responded with a stimulus response - the so-called threshold. The scientists measured cell activity before, during and after exploration. Therefore they could compare the behavior of silent cells and place cells before the first site-specific activity. They found that place cells showed from the outset a lower threshold and different discharge patterns.

The scientists assume cell-intrinsic properties to be responsible for these differences. This triggers a series of new questions: What factors account for the differences? How are these cell properties set? Are these properties changed if other cells are active in a different environment? In humans, the hippocampus is central for the transformation of content of the short-term into the long-term memory. Dysfunctions in this brain region result in anterograde amnesia. In such cases, memories remain, but new information cannot be permanently stored. With their results, scientists contribute to a better understanding of our memory.

To view the article:
Epsztein J., Brecht M., Lee A., Intracellular Determinants of Hippocampal CA1 Place and Silent Cell Activity in a Novel Environment Neuron (2011), Volume 70, Issue 1, p. 109-120.

Prof. Dr. Michael Brecht
Bernstein Zentrum Computational Neuroscience Berlin
Humboldt-Universität zu Berlin
Philippstr.13, Haus 6
10115 Berlin
Phone: +49 30 2093-6772