Recent findings from a team of British researchers point to multiple factors that may contribute to the onset of unwanted, distressing memories in people with PTSD. The unwanted reliving of traumatic memories while sleeping or awake is one of the four classic symptoms of post-traumatic stress disorder (PTSD). In a study review published in 2015 in the Journal of Psychology, researchers from the United Kingdom\u2019s King\u2019s College London explored the possible explanations for the onset of these persistent and unpleasant memories in PTSD-affected individuals. The researchers identified three such explanations, including the ways in which people with PTSD interpret and respond to the naturally occurring memories of their prior highly traumatic experiences. PTSD In addition to unwanted, distressing memories that appear during waking hours or during nightmares, the core symptoms of PTSD include a sharp uptick in daily negativity and \u201cdown\u201d moods, an inability to shut down the hyper-alert state that characterizes the body\u2019s natural \u201cfight-or-flight\u201d response and a compelling wish to stay away from anything that serves as a reminder of previous exposure to sources of emotional trauma such as major accidents, combat, sexual or physical assault, natural disasters and acts of terror. Roughly one-fifth of all women will develop some version of these symptoms in the aftermath of their highly traumatic experiences. About 8 percent of all men exposed to such experiences will develop the disorder. Under current guidelines used throughout the U.S., PTSD is not officially diagnosable in the one-month period following trauma exposure. This is true, in part, because the average person will naturally experience some sort of trauma reaction before recovering his or her mental health and well-being over a relatively short span of time. A sizable minority of trauma-exposed individuals will develop an amplified, dysfunctional form of this normal reaction and thereby qualify for a short-term diagnosis called acute stress disorder or ASD. Most people diagnosed with ASD will eventually develop PTSD. However, not all people with ASD will qualify for a PTSD diagnosis, and some people with PTSD never experience any adverse stress reactions until the one-month deadline for diagnosing acute stress disorder has passed. PTSD and Unwanted Memories People who live through traumatic experiences typically remember those experiences (although some individuals may develop a form of amnesia associated with trauma exposure). While trauma-related memories can cause considerable discomfort, they typically take on a less distressing quality over time as they\u2019re gradually incorporated into a larger body of life experiences. In a person with PTSD, trauma-related memories retain their power to disorient and disturb, rather than fading in intensity with the passage of time. Some affected individuals experience waking traumatic memories commonly known as flashbacks, while others relive traumatic situations or events in their sleep in the form of nightmares. An individual with PTSD may also experience a combination of flashbacks and nightmares. How Do Unwanted Memories Form? In the study review published in the Journal of Psychology, the King\u2019s College London researchers used findings from a large number of previously conducted studies to explore the potential underlying reasons for the persistent and distressing trauma-related memories of people with PTSD. These researchers preliminarily concluded that the memories of trauma-exposed people who develop the disorder are largely similar to the memories of trauma-exposed people who don\u2019t develop the disorder. However, several key differences emerge. Specific qualities that distinguish the memories of PTSD-affected individuals include an unusual sense of immediacy to memory content, loss of the ability to place trauma-related memories in a larger context, a greater likelihood of experiencing trauma-related memories that are triggered by seemingly unrelated situations and a higher chance of viewing relived memories as a source of substantial personal distress. The researchers concluded that there is no clear consensus for the underlying cause of unwanted, PTSD-associated memories. However, they believe that three current theories may at least partially help explain this phenomenon. In some cases, people with PTSD may undergo changes in memory processing that make them more susceptible to the uncontrolled triggering of trauma-related memories. In other cases, people with the disorder may interpret their trauma-related memories in specific ways that increase the memories\u2019 ability to cause a distressing emotional\/psychological reaction. In still other cases, people with PTSD may develop behaviors and thought processes that increase their chances of re-experiencing their traumatic memories. In all likelihood, all of these factors affect any given person with the disorder to one degree or another.