A 59-year-old man presents to the ED for sudden-onset dizziness and unsteady gait that began 2 hours ago. He also reports numbness and burning pain on the left side of his body. On exam, he has left-sided ptosis and miosis. Strength is 5/5 throughout. Pinprick sensation is decreased on the left arm and leg. Vibration and joint position sense are intact. Which of the following brainstem pathways is most directly responsible for the autonomic finding in this patient?