Peter Huttenlocher

During the 1960s and well into the 1970s the focus of Peter Huttenlocher’s research, as would be expected from a paediatric neurologist at the time, was neurological defects and abnormalities. He was already widely recognised as an authority on the diagnosis and treatment of children with Reye’s syndrome, tuberous sclerosis, and various seizure disorders.

In the late 1970s, however, Huttenlocher’s research interest would take a 180 degree turn. Instead of focusing only on defective parts of the human brain, he began studying the gridwork of healthy and properly functioning brains. The switch happened during a project designed to document abnormal synaptogenesis in the cerebral cortex of people with intellectual disabilities.

Years later Huttenlocher said, “Paradoxically, in our early studies, the findings in the normal population were more interesting than the abnormal population.”

Huttenlocher and colleagues collected, through autopsies, “21 normal human brains ranging from newborn to age 90 years.” Using an electron microscope, Huttenlocher photographed synapses and counted. He counted at his laboratory, and he counted at home. He counted billions of synapses.

He showed that synaptic …