Scientists have long believed that constructing memories is like playing with neurological Tinkertoys. Exposed to a barrage of sensations from the outside world, we snap together brain cells to form new patterns of electrical connections that stand for images, smells, touches and sounds.
The most unshakable part of this belief is that the neurons used to build these memory circuits are a depletable resource, like petroleum or gold. We are each bequeathed a finite number of cellular building blocks, and the supply gets smaller each year. That is certainly how it feels as memories blur with middle age and it gets...