The correct answer is - brain drain.
The brain drain process is a process that appears when the population is declining through migration. With a migration in which mostly the younger population that has higher education is leaving to live in other places, the region is losing the young and prosperous minds, thus being in a process of brain drain.
With the suggested situation that the population is growing in the region, the result will for sure not be to have a brain drain process. Instead, it will be more of a situation of brain gain, as there's more and more people in the region.