Washington: Regarding “Elon Musk, monkeys and our human responsibility” (op-ed, March 14): Four decades ago, scientists mapped the neuronal structure of the macaque monkey brain and subsequently applied deep brain stimulation (DBS) to brain regions tied to symptoms of Parkinson’s disease. It worked. The monkeys had markedly reduced symptoms. The first human DBS procedure proved successful. Today, more than 160,000 patients worldwide have undergone successful DBS for Parkinson’s and other neurological disorders.