A 71-year-old right handed man with a long history of cigarette smoking and hypertension had an episode 5 months before admmisione of "right hand weakness and speech difficulty, and mixing up words". Since then, he has had several episodes, lasting few minutes each, of dim, blurry vision in the left eye. Finally,  he fell on three separate occasions when his righ leg suddenly gave out, most recently on the day of admission. Examination was normal except for high-pitched bruit over the left carotid artery.

What is the most likely cause of this patient transient neurological episodes?

For each type of episode shown in bold above, indentify the branch of the internal carotid artery that could be responsible for the patient's symptoms.