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CA neurons

Unlocking the Brain’s Memory Retrieval System

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Memory Trace in Mouse Hippocampus

Credit:Sahay Lab, Massachusetts General Hospital, Boston

Play the first few bars of any widely known piece of music, be it The Star-Spangled Banner, Beethoven’s Fifth, or The Rolling Stones’ (I Can’t Get No) Satisfaction, and you’ll find that many folks can’t resist filling in the rest of the melody. That’s because the human brain thrives on completing familiar patterns. But, as we grow older, our pattern completion skills often become more error prone.

This image shows some of the neural wiring that controls pattern completion in the mammalian brain. Specifically, you’re looking at a cross-section of a mouse hippocampus that’s packed with dentate granule neurons and their signal-transmitting arms, called axons, (light green). Note how the axons’ short, finger-like projections, called filopodia (bright green), are interacting with a neuron (red) to form a “memory trace” network. Functioning much like an online search engine, memory traces use bits of incoming information, like the first few notes of a song, to locate and pull up more detailed information, like the complete song, from the brain’s repository of memories in the cerebral cortex.

Snapshots of Life: Color Coding the Hippocampus

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Credit: Raunak Basu, University of Utah, Salt Lake City

The final frontier? Trekkies would probably say it’s space, but mapping the brain—the most complicated biological structure in the known universe—is turning out to be an amazing adventure in its own right. Not only are researchers getting better at charting the brain’s densely packed and varied cellular topography, they are starting to identify the molecules that neurons use to connect into the distinct information-processing circuits that allow all walks of life to think and experience the world.

This image shows distinct neural connections in a cross section of a mouse’s hippocampus, a region of the brain involved in the memory of facts and events. The large, crescent-shaped area in green is hippocampal zone CA1. Its highly specialized neurons, called place cells, serve as the brain’s GPS system to track location. It appears green because these neurons express cadherin-10. This protein serves as a kind of molecular glue that likely imparts specific functional properties to this region. [1]