Jess Is Fast Asleep

Multiple Choice

Jess is fast asleep. Her roommate, Crystal, is studying in the next room when their cat knocks a lamp off the bookshelf. Crystal jumps up from her desk, but Jess remains asleep. What brain structure is responsible for raising or lowering the thresholds of conscious awareness such that Crystal reacts to the stimulus while Jess does not?

A) The reticular formation
B) The substantia nigra
C) The medial parietal cortex
D) The corpus callosum