This article states:
Once the neural tube closes, at around week 6 or week 7 of pregnancy, it curves and bulges into three sections, commonly known as the forebrain, midbrain and hindbrain. Just to the rear of the hindbrain sits the part that will soon turn into your baby's spinal cord. Soon, these areas bubble into those five different regions of the brain that we're most familiar with: the cerebrum, cerebellum, brain stem, pituitary gland and the hypothalamus.
How "soon" after 6 - 7 weeks is this soon the article talks about? When does the brain stem appear in humans?