Neuroscientific research on monkeys is ethically troubling—but vital

THE HUMAN brain may be the most complex object on Earth. It contains 85bn nerve cells and trillions of interconnections. As these cells process information, people experience consciousness and thought. The brain is made even more mysterious by the fact it is scrutable only when alive. To truly understand brains means examining them while they are functioning inside the body.Few humans in their right mind would volunteer to plug today’s instruments and sensors into their living brains. Doing so often involves having someone drill into your skull, with the risk of infection or brain damage. And so neuroscientists seeking to understand human brains turn to humanity’s nearest animal relatives, primates.