Neuromaturation of the human fetus.

The fetal human possesses an active central nervous system from at least the eighth week of development. Until mid-gestation the most significant center of activity is the brainstem. By the end of the first trimester, it appears that the brainstem could be acting as a rudimentary modulator of sensory information and motor activity. What importance ought to be attached to such regulatory activity is uncertain. Some argue that it represents a level of integrated activity sufficient to bolster an argument for conferring some measure of standing at this point. Our thinking about sentience is not advanced a great deal, as we as yet have no good way of talking about it at the brainstem level. As for the neocortex, available evidence indicates that it does not become a functional part of the neuraxis until at least mid-gestation. It is not until then that the thalamus--the major gateway for sensory input to the cerebrum--makes its first afferent contacts with the neocortex.