Memory loss refers to the loss of memory. There are many types of memory loss, the most common being selective memory loss and memory loss caused by Alzheimer’s disease. Selective amnesia usually occurs after a large emotional stimulus, head trauma, and a short-term partial memory loss. It is usually impossible to recall what happened during the injury or emotional stimulation, and it is difficult to recover this part of the memory afterward. Age-related memory loss is related to Alzheimer’s disease. As the brain shrinks and its functions deteriorate with age, some elderly people develop senile dementia, which is usually characterized by recent memory loss or even absence. For example, if the patient is asked what he or she did yesterday or what he or she ate for dinner, the patient usually cannot answer. However, long-term memory is generally unaffected, for example, patients are able to answer questions about things that happened in earlier years.