1OO,OOO,OOO,OOO
Estimated number of brain cells in the average adult brain


10 Billion
Estimated number of brain cells lost by the average adult over a lifetime


200 Million
Estimated number of additional brain cells
lost by an average Alzheimer’s patient


85,OOO
Estimated number of brain cells lost
by the average adult each day


2OO Million
Miles of neurons formed if every
brain cell in the average adult brain
were arranged end to end

A pair of twins is born, and both infants begin to develop normally. By their first birthday, however, the male sibling has begun to diverge from his sister, showing less eye contact and affection. He often wears a spaced-out expression and fixates on certain puzzles and patterns. By age three, his mounting symptoms lead to a diagnosis that has become disturbingly routine in recent years: autism.

What causes the disease, which now strikes 1 in every 166 children, and why does it affect four times as many boys as girls?