a battle, to when the person was no longer in immediate danger. in processing the memory in these ways it becomes less likely to intrude into their thoughts as an unwanted flashback. the memory also becomes less vivid, less distressing and seems more distant to the person's present life. eye movement desensitization and reprocessing (emdr) main article: eye movement desensitization and reprocessing eye movement desensitization and reprocessing (emdr) is a therapy for treating traumatic memories that involves elements of exposure therapy and cognitive behavioral therapy. despite controversy remaining in some quarters, emdr is rated at the highest level of efficacy for ptsd by numerous organizations, most notably by the international society for traumatic stress studies in a comprehensive study of all effective treatments for ptsd. there is an extensive theoretical model called adaptive information processing (aip) underlying emdr. the role and mechanism of eye movements, or more generally, bilateral, dual attention stimulation (bls) is still unclear, and though early studies cast doubt on their necessity for emdr's efficacy, bls is still considered an integral part of the system by most practicing therapists. emdr begins by identifying troubling memories, cognitions and sensations a patient is struggling with. then negative thoughts are found that the patient has associated with each memory. while both memory and thought are held in mind the patient follows a moving object with their eyes. after, a positive thought about the memory is discussed in an aim to replace the association the negative thought has to the memory with a preferable thought. experiments have shown that targeted negative memories are recalled less vividly and with less emotion after treatments with emdr. skin conductance responses, a measure of stress and arousal, have also shown lower levels when negative memories treated with emdr were brought to mind. a possible mechanism for emdr has been proposed. as memories are recalled they enter a labile state, where they become vulnerable to being forgotten again. normally these memories would be reconsolidated, becoming stronger and more permanent again. adding in eye movements creates extra demand on working memory (which keeps currently-used information available). this makes it difficult for all the details of the memory to be held at once. once the memories are reconsolidated they are less emotional and vivid. video gaming emily holmes at the university of oxford ran an experiment that showed the video game tetris could be a potential method of reducing the strength of traumatic memories. the experiment involved participants watching emotionally distressing video footage. compared with a control group the participants who played tetris experienced far less intrusive and upsetting thoughts about the footage over a week-long period. the ability to recall details of the footage was not impaired by playing tetris. another group of participants exposed to the same footage were given a different task as a distractor, a verbal "pub quiz" game. this involved answering trivia questions from a range of topics unrelated to the distressing video footage. those in the pub quiz condition were more likely to experience flashbacks compared to both a no-task, waiting a comparable amount of time without an activity, and the tetris conditions. holmes and colleagues thus concluded that it was not merely that those playing tetris were distracted but that they were distracted in a way that served to disrupt the formation of unwanted and intrusive memories. the explanation given for the success of administrating tetris as opposed to other interventions is that tetris draws heavily on visuospatial processing power. because the brain only has a limited supply of resources to process information, playing tetris hinders the ability of the brain to focus on other visual information, such as traumatic images. however, the details of the event can still be thought of and rehearsed verbally, as tetris should not interfere with verbal processes of the brain. this explains why participants could remember the details of the footage they watched but why they still experienced fewer flashbacks. neuroscience has shown that memories are vulnerable to disruption for several hours after they form. holmes and colleagues proposed that because of this visuospatial distractors like tetris, if administered within six hours of a traumatic event could help prevent symptoms of flashbacks. also there is some evidence that memories can become vulnerable to disruption even at longer periods of time in a process known as reconsolidation. ethical concerns the prospect of memory erasure or alteration raises ethical issues. some of these concern identity, as memory seems to play a role in how people perceive themselves. for example, if a traumatic memory were erased, a person might still remember related events in their lives, such as their emotional reactions to later experiences. without the original memory to give them context, these remembered events might prompt the subjects to see themselves as emotional or irrational people. in the united states, the president's council on bioethics devoted a chapter in its october 2003 report beyond therapy to the issue. the report discourages the use of drugs that blunt the effect of traumatic memories, warning against treating human emotional reactions to life events as a medical issue. issues of self-deception arise when altering memories as well. avoiding the pain and difficulty of dealing with a memory by taking a drug may not be an honest method of coping. instead of dealing with the truth of the situation a new altered reality is created where the memory is dissociated from pain, or the memory is forgotten altogether. another issue that arises is exposing patients to unnecessary risk. traumatic experiences do not necessarily produce a long term traumatic memory, some individuals learn to cope and integrate their experience and it stops affecting their lives quite quickly. if drug treatments are administered when not needed, as when a person could learn to cope without drugs, they may be exposed to side effects and other risks without cause. loss of painful memories may actually end up causing more harm in some cases. painful, frightening or even traumatic memories can serve to teach a person to avoid certain situations or experiences. by erasing those memories their adaptive function, to warn and protect individuals may be lost. another possible result of this technology is a lack of tolerance. if the suffering induced by traumatic events were removable, people may become less sympathetic to that suffering, and put more social pressure on others to erase the memories. despite potential risks and abuses, it can still be justifiable to erase traumatic memories when their presence is so disruptive to some and overcoming them can be a difficult process.