Memory dynamics: the cellular architecture of systems memory

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The human brain contains approximately 80 billion nerve cells (neurons). When you learn something new, which of those neurons will be involved in storing that information? Are all neurons equal, or are some more likely than others to store memories? Will a memory always involve the same neurons? Or will the memory trace (known as an 'engram') change over time, allowing you to file memories appropriately, remembering the important information and updating the engram with new knowledge?These questions are all very challenging to answer. But if we do not answer them, we can never understand how the brain works, or how to treat memory disorders associated with illnesses such as dementia, depression and schizophrenia.Over the past few years, technology has advanced to the point at which we can - at least in mice - "capture" the groups of neurons involved in learning a specific memory. These neurons are known as 'engram neurons', and were first discovered in a part of the brain called the hippocampus, which acts as a central indexing system for memory files in all mammals. We can activate engram neurons (to trigger recall of the memory) or silence them (to delete a memory). These methods have transformed our understanding of memory mechanisms over the past 2 years, but they are very new and evolving rapidly, as is out ability to measure brain activity from hundreds of neurons simultaneously.In this 3-year series of experiments, we will combine capture of engram neurons with recording the activity from large populations of neurons in mouse hippocampus and connected brain regions to translate the algorithms used by engram neurons to learn, process and remember new information. This project would not be possible without the international team of neuroscientists involved, which spans the UK and Japan, uniting complementary expertise in genetics, psychology, computational analyses and electrical engineering.We will also measure, for the first time, the activity of engram neurons during sleep. We have known for 2000 years that sleep supports healthy memory, but we still do not know precisely how. Now we have discovered engram neurons, the answers may be within reach.Given that your entire personality and worldview are products of the many memory engrams stored by your brain, neuroscience of this type remains essential if we are to understand the fundamental biology of life and disease.