The Brain's Pulse Delivers Drugs
Fluid flows in the narrow gaps between brain cells. It doesn't stay still: each heartbeat pushes it forward, and breathing adds its own waves. This was seen in images ten years ago, but only now have researchers calculated how this pulsing accelerates molecules.
If you drop ink into a stream, it drifts with the current. But if the stream speeds up and slows down, the ink spreads wider.