Transient global amnesia has been explained by epileptic mechanisms or transient ischemic attacks affecting the hippocampus. None of these two mechanisms appear likely. The animal experimental phenomenon entitled spreading depression of cortical electrical activity (SD) or spreading depression of Leao has been implicated in migraine pathogenesis and may be relevant to transient global amnesia. In experimental animals, SD in the hippocampus causes a temporary functional ablation lasting minutes to hours with full functional recovery. Glutamate, which is present in large amounts in the hippocampus, may experimentally elicit spreading depression, and strong emotional events may possibly liberate glutamate and bring about this reaction in human patients.