Knowing that neurons are able to grow in the adult brain gives us a chance to enhance the process and explore under what conditions — genetic, sensory or other — we can make that happen.

The scale of change is much smaller than what goes on during the critical period of development, but the fact that it goes on at all is earth-shattering.

Maybe the inhibitory network is where the capacity is for large-scale changes. What’s more, this growth is tied to use, so even as adults, the more we use our minds, the more robust they can...