Okarma said FDA scrutiny was stringent, and that researchers studied the cells in petri dishes and in animals before obtaining permission to test them in humans.

CNN: FDA approves human embryonic stem cell study

The first light-activated neurons were cultivated as layers of cells in Petri dishes, but researchers were quickly able to make the technique work in flies, worms, zebrafish, mice, and monkeys.

WSJ: Scientists Cast Light Onto Roots of Illness Deep in the Brain