The papers, all published in the journal Nature, suggest that during sleep, slow electrical waves push the fluid around cells from deep in the brain to its surface.

The new studies come more than a decade after Iliff and Dr. Maiken Nedergaard, a Danish scientist, first proposed that the clear fluids in and around the brain are part of a system to wash away waste products.

It turned out that the waves were acting as a signal, synchronizing the activity of neurons and transforming them into tiny pumps that push fluid toward the brain's surface, the team reported in February in the journal Nature.

In a second paper published in the same issue of Nature, a team led by scientists at the Massachusetts Institute of Technology provided more evidence that slow electrical waves help clear out waste.

In a paper published a few weeks earlier, Kipnis had shown how waste, including amyloid, appeared to be crossing the protective membrane that usually isolates the brain.

So finding ways to help the brain clean itself — perhaps by inducing those slow electrical waves — might prevent a wide array of disorders.

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