The ________ levels are fully developed at birth and regulate most reflexes and fundamental activities in the body.

The subcortical levels are fully developed at birth and play a crucial role in regulating most reflexes and fundamental bodily activities. These areas of the brain, which include structures such as the brainstem and the basal ganglia, are responsible for essential functions such as heart rate, breathing, and basic reflex responses. They operate autonomously and are vital for the survival of the newborn, as they control basic life-sustaining functions without requiring higher cognitive processing.

In contrast, cortical levels are not fully developed at birth; they continue to mature significantly in the first few years of life. The peripheral system refers more to the network of nerves outside the central nervous system and does not directly engage in the regulation of reflexes and fundamental activities. Gray matter encompasses various regions of the brain, including both subcortical and cortical structures, but the specific development of reflex regulation is attributed primarily to the subcortical areas at the time of birth.