We can now watch the brain store long-term memories.
A team at Stanford University has persuaded 13 volunteers to go to sleep in an fMRI scanner. They also made them learn a task just before nodding off. The scanner was at first able to observe the brain replay this learning over and over in the cortex. The exciting part of the experiment occurred when the volunteers entered non-REM sleep. The replay activity progressively damped down in the cortex. As it did so, replay activity took over in the putamen (sub-cortical). (This would indicate that the memory in this case is implicit or non-declarative.) The team proposes that they are witnessing the brain transferring a newly learnt memory from short-term to long-term storage. In this way, the cortex is free to go back out into the world and learn new things all over again.
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