As his former National Institutes of Health (NIH) colleague Irwin Feinberg put it, Peter’s research “took a 180-degree turn” after his move to the University of Chicago in 1974. Instead of focusing on the brains of patients with neurological deficits, he started to study the “gridwork” of healthy brains. As Peter said, “the findings in the normal population were more interesting than the abnormal population.” His landmark 1979 study published in Brain Research was unexpected [1]. The accepted thinking at that time was that brains actually get more connections as we learn and develop, but he found the opposite to be true. After a burst of new synapses form in the first year of life, unneeded connections are removed, or pruned. All scientific discoveries are incremental and build on the work of other scientists. But rarely, a scientific discovery can also present an entirely new way of thinking about a problem – and is truly a breakthrough. In a conversation in May 2022, Feinberg said about Peter’s work: “the idea of brain connections was not in the thinking in the 1980s. The skeptics were many.”