Now the instructions for building your brain get more complicated, since you will be rigging up the wiring that permits complex conversations involving billions of brain cells.

This image shows one network of neurons from the cerebellum of a mouse. The brilliant white blobs are Purkinje cells, large neurons that allow the animal to coordinate complex movements. The cells' dendrites form the feathery outer fringe, and the axons gathered in the middle dive into the depths of the cerebellum to send signals within.

Early in postnatal development, before this bouquet of cells makes connections with other types of neurons, the cells engage in cross-talk among themselves, Michael Hausser has found. The cells send synchronized waves of electrical impulses back and forth, almost like a dress rehearsal to help them learn how to hook up with other parts of the brain.

Without nature's innate processes to guide you, your wiring job would be very challenging--even if you were an experienced electrician.