Memory loss is one of the most prominent signs of depression. A depressed person appears to recall mainly sad, negative memories. To family and friends this can appear to be memory loss. Depression also inhibits a person’s ability to create long term memory. However, some researchers believe this is due to inattentiveness and lack of concentration.

Depressed people generally have decreased levels of serotonin. Serotonin regulates blood flow, providing cells with the fuel they need to operate. Serotonin is also involved in regulating our arousal levels – including the degree to which we are focused and attentive. A depressed person, therefore, may be too inattentive and unfocused to file passing events from their working memory into short-term memory. In this case, it isn't so much that the depressed person has forgotten, but that the memory was never stored in the first place.