An 83-year-old man comes to the office because 2 days ago he had an episode of garbled speech that lasted ≤1 minute. He is accompanied by his wife, who describes the sudden onset of word-finding difficulty, during which he substituted the word "juice" with the word "fuse" and was unable to follow her instruction to sit down in the kitchen chair. There were no other signs before or since the event. History includes a lacunar stroke 6 years ago, hypertension, diabetes mellitus, and hyperlipidemia. Current medications are atorvastatin, lisinopril, hydrochlorothiazide, metformin, and aspirin (81 mg/d); he has not missed any doses. On examination, blood pressure is normal, and heart rate is 78 beats per minute. There are no carotid bruits, and cardiac auscultation is normal. There is a left facial palsy, which has been present since his stroke 6 years ago. Speech and language findings are normal, and there are no new focal neurologic deficits. Which one of the following should be done first?
a. Increase aspirin dosage to 325 mg/d.
b. Begin warfarin
c. Order carotid Doppler ultrasound.
d. Order electroencephalography (EEG).