Damage to the posterior temporal lobe of the dominant hemisphere is the cause of Wernicke's aphasia. The etiology of this damage can vary greatly, with the most common cause being a cerebrovascular event such as an ischemic stroke. Ischemic stroke is the result of a thrombus occluding a blood vessel, restricting blood supply to a particular area of the brain. Other causes of focal damage potentially leading to Wernicke's aphasia include head trauma, infections affecting the central nervous system, neurodegenerative disease, and neoplasms. A cerebrovascular event is more likely the cause in an acute-onset presentation of aphasia, whereas a degenerative disease should be suspected in aphasia with gradual progression over time. Imaging is often useful in identifying a lesion, with most common initial imaging consisting of computed tomography (CT) scan or magnetic resonance imaging (MRI). Electroencephalography (EEG) can also be useful in patients with transient aphasia, where findings may be due to seizures, although this is a less common cause.