ABSTRACT
It is unlikely that the wisest 18th-century scholar, with unlimited time and an extravagant reward for the correct solution, would have imagined the details of brain development that have been discovered over the past quarter century. This corpus of information contains many surprises. For example, the cortex is composed of six layers, each with a distinct function, that develop in an inside-out fashion. The second surprise is that although the axonal tracts that mediate motor behavior develop before those that mediate sensation, the newborn can see, hear, feel, taste, and smell, but has relatively poor motor coordination. Perhaps the most counterintuitive discovery is that the 8-month-old infant has many more synapses in the visual cortex than the 8-year-old. A brilliant 18th-century scholar in a mood of exuberant originality would have rejected this idea as bizarre if it occurred on a sunny June morning.
