involuntary memories. In clinical disorders Posttraumatic stress disorder Often people who have been the victims of some type of trauma describe vivid memories that intrude on their thoughts spontaneously and without warning. Such mental intrusions, if maintained over time compose the hallmark symptom of posttraumatic stress disorder (PTSD). The DSM-IV defines a trauma as an event in which someone experiences, or witnesses' severe injury to themselves or others or a threat to their integrity. The person must also have responded with fear, helplessness or horror at the time of the trauma. The main psychological consequences of this include re-experiencing the traumatic event (through both intrusive thoughts and images), avoidance of trauma-related stimuli, and increased arousal levels. When it comes to involuntary memory, researchers are mainly interested in the concept of these trauma-related intrusions, which generally involved some form of re-experiencing the event, including a sensory component (e.g., imagery in any modality be it visual, auditory etc.). These intrusions, often termed "flashbacks", make the victim feel as though they are reliving the trauma, and cause high levels of emotional arousal, and the sense of an impending threat. Typically, they are parts of the traumatic event that were most salient at the time, known as "hotspots" and have the definitive feature that they cause high levels of emotional distress, and may be difficult to recall deliberately. Although this is a defining feature of PTSD, intrusive memories are also frequently encountered in anxiety-based disorders, psychotic disorders and even within the general population. Regardless of the context in which they are encountered, intrusions tend to have the same central feature; that the stored information is being recalled involuntarily. It is thought that intrusions arise when an individual encounters stimuli similar to the stimuli that were processed and stored during the trauma, thus triggering the memory into the conscious mind. A common example is one in which someone who has the victim of a car crash, upon hearing the screeching of tires experiences a flashback of their own collision, as if they are back at the original event. Psychosis Stressful and traumatic events, which may manifest as involuntary memories called flashbacks, may trigger a wide range of anxiety-based and psychotic disorders. Social phobia, bipolar disorder, depression, and agoraphobia, are a few examples of disorders that have influences from flashbacks. Psychosis is defined as a range of perceptual presentations, with the associated symptoms frequently referred to