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Monday, 25 June 2012
A Whole Hippocampus Reveals Its Secrets

Theta-waveSome major scientific discoveries are the result not so much of a particular experiment as of the lengthy efforts to develop the protocol used in it. Such was the case for a study that Sylvain Williams published in Nature Neuroscience in November 2009. Williams and his team had worked for years to refine the method used in this study to record neuronal activity in a whole rat hippocampus preserved in vitro.

The more traditional method, in which researchers record the activity of neurons in a thin slice of hippocampal tissue, is much simpler but necessarily destroys huge numbers of neural circuits internal to the hippocampus—for example, all of the axons that pass through the slice perpendicularly.

It should be no surprise, then, that the very first recordings that Williams and his team made with a whole hippocampus successfully dispelled a misconception that had been accepted for many decades. The theta rhythm—the major rhythmic pattern of discharge of the neurons of the hippocampus—does not necessarily come from an external structure (the septum), as had always been believed, but can come from the hippocampus itself!

In other words, this experiment clearly demonstrated something that hundreds of previous studies with hippocampal slices had failed to show. Given how critically important theta rhythms are for learning and memory, this study’s finding that these rhythms can emerge endogenously in the hippocampus, and specifically in its CA1 sub-region, raises some interesting questions for the future. For example, what kinds of interneurons in CA1 are involved in generating theta rhythms, and how are these rhythms integrated with the other rhythms observed in the cortex, such as gamma rhythms?

i_lien Researchers at the Douglas redefine the role of a region of the brain associated with organizing memory
a_exp Hippocampal theta rhythms follow the beat of their own drum + Self-generated theta oscillations in the hippocampus

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