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What these findings tell us is that the meaning of a nerve impulse triggered in a place cell at any given point in time will depend on its relationship to the particular phase of a rhythmic wave pattern that is occurring in the background at that same time. And these place cells fired in the exact same sequence (only sped up) as when the rat had actually been moving down the corridor past their receiving fields! Not only that, but when the rat reached the end of the corridor and began eating its reward, the researchers observed other sharp waveвЂ“ripples while its hippocampus played back (this time in reverse) the same sequence of place-cell firings as when it had been making the trip, as if the rat were re-encoding this precious sequence that had led it to its yummy treat!

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ThatвЂ™s already pretty interesting, but thatвЂ™s not all! In one set of experiments, scientists recorded the activity in a ratвЂ™s hippocampus as it travelled down a linear corridor to get a food reward, Once the rat had completed a few trips down the corridor, the scientists watched the rat stand motionless before starting its next trip, while a series of place cells fired and sharp waveвЂ“ripples were triggered in its hippocampus. On the basis of such observations and many others, some scientists have hypothesized that the sharp waveвЂ“ripples of the hippocampus enable the retrieval of memories that can then be used immediately by other brain circuits downstream that are involved in decision-making, planning, recollection and/or imagination, while simultaneously initiating memory-consolidation processes. In experiments with rodents, disrupting these patterns disrupted the animalsвЂ™ memories, as observed through their behaviour. For example, neuroscientists have discovered that the sharp waveвЂ“ripples (rapid oscillations at frequencies of 150 to 200 Hz) that are specific to the hippocampus can represent past and potential future experiences. But to discuss them in any greater depth, you really canвЂ™t avoid talking about brain rhythms. The fact is that nowadays, we know a lot more about these phenomena. Or you might read that your recently acquired memories are consolidated while youвЂ™re asleep or reconsolidated when you retrieve them, and that the hippocampus is somehow involved, but thatвЂ™s it.

ThatвЂ™s just about all that a lot of textbooks have to say on the subject-nothing about what specific mechanism might be involved. One good example is the consolidation of learning, which is associated with certain types of neural activity in the hippocampus. But unfortunately, college and university neuroscience textbooks discuss the brainвЂ™s neural rhythms only very superficially, even though they are actually starting to shed light on many different scientific mysteries. These patterns, which have different frequencies, are one of the neuronsвЂ™ preferred means of communicating with one another. Whether your support is moral, financial, or both, thank you from the bottom of our hearts!Д«runo Dubuc, Patrick Robert, Denis Paquet, and Al DaigenДЄn example of the importance of our brain rhythmsДЄ large majority of the neurons in the human brain display rhythmic activity patterns-in other words, they send out one nerve impulse, then go quiet, then send out another nerve impulse, and so on.

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Please, rest assured that we are doing our utmost to continue our mission of providing the general public with the best possible information about the brain and neuroscience in the original spirit of the Internet: the desire to share information free of charge and with no adverstising. We must therefore ask our readers for donations so that we can continue updating and adding new content to The Brain from Top to Bottom web site and blog. But we have not managed to find the funding we need. We have approached a number of organizations, all of which have recognized the value of our work. After providing all the funding for The Brain from Top to Bottom for over 10 years, the CIHR Institute of Neurosciences, Mental Health and Addiction informed us that because of budget cuts, they were going to be forced to stop sponsoring us as of March 31st, 2013.