Answer: Reticular formation
Explanation:
Reticular formation is defined as the process in which nuclei of the brains stem get interconnected without any particular defined pattern.This link impacts the consciousnesses of any individual like, sleep, awake and awareness through signals sent to cerebrum.
According to the question, sleepiness caused in Stephanie while being in lectures or other times is due to recticular formation because the brain stems are linked with the sleep and alertness