What are the likely causes of brain blood clots and what are their symptoms?

Artery/Fibrillation: Most strokes are due to clots to the brain. These occur due to clots from the heart in those with atrial fibrillatiion and those with plaque in the carotid arteries. Small clots form, travel up to the brain and occlude small arterioles and thus a small stroke. There are other causes but those are the most common. That is why Coumadin (warfarin) and Aspirin are used in prevention of clot formation.