Great Aunt Mary has always been a "lark," getting up early, working busily during the day and then going to bed relatively early. She recently had a slight stroke, and the only thing that seems different about her is that her normal periods of sleeping and waking have changed. Now, you never know when she will get up or when she will go to bed, and she is often up half the night but sleeping

during the day. Given what you have learned about sleep and waking, which one of the following brain areas might have been affected by her stroke?

a. the rubrospinal tract
b. the retinohypothalamic pathway
c. the mesolimbicstriatal pathway
d. the thalamopituitary pathway

b