If there is an injury to the central nervous system such as after a stroke, the brain needs to compensate for this by reorganising itself. To do this, a dense network of molecules between the nerve cells -- known as the extracellular matrix -- must loosen. This is the job of a wide variety of enzymes that ultimately regulate how plastic or how stable the brain is. Researchers studied what happens when certain enzymes are blocked in mice. Depending on whether the brain is healthy or diseased, the inhibition had opposite effects.