The incidence of perinatal stroke is relatively common, as high as 1 in 2,300 births, but little is known about the resulting changes in the brain that eventually manifest as cerebral palsy (CP). More importantly, no therapy has been devised to mitigate these specific maladaptive changes leading to hemiplegic CP. However, motor signs that indicate the infant is beginning to develop CP often do not become evident for several months after the diagnosis of perinatal stroke. This delays therapy. We view the first several months after perinatal stroke as a "window of opportunity" because it is known to be a critical period of development. During this period, a well-designed intervention could minimize maladaptive changes in the brain. To design such a science-based rehabilitation protocol for young infants during this window of opportunity, we must first develop efficient and reliable assessments to detect and measure maladaptive cortical reorganization in the brain.