Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Stroke ?
    ### Response:
    Ischemic Stroke and Transient Ischemic Attack
                
An ischemic stroke or transient ischemic attack (TIA) occurs if an artery that supplies oxygen-rich blood to the brain becomes blocked. Many medical conditions can increase the risk of ischemic stroke or TIA.
    