Here's a reference to an interesting 2009 study showing that playing tetris for 30 minutes can interfere with memory consolidation of upsetting visual imagery:
This is an example of evolving evidence that an important period for consolidation of memories occurs in the first 24 hours after an experience. A consolidated implicit association between the factual components of memory and strong negative emotions may also form most strongly during this initial post-exposure period.
The same group published a 2010 study showing that a game like tetris was more effective than a quiz-type game activity for reducing visual flashbacks following exposure to upsetting imagery:
I think the message here is not that tetris in particular has some kind of unique medicinal properties, but that a non-passive activity which requires continuous, intense visual attention is most effective at reducing consolidation of intrusive visual memory. A distracting activity lacking strong visual involvement may be less likely to interfere with this consolidation mechanism.
Other research has suggested that propranolol, a beta-blocking drug, can reduce post-traumatic memory consolidation, particularly the troubling implicit or emotional component responsible for psychological symptoms of PTSD. (see my other post, http://garthkroeker.blogspot.com/2009/02/beta-blockers.html)
Some of the standard psychological treatments in the immediate post-trauma period may be harmful, such as critical incident stress debriefing. If individuals are compelled to revisit details of their trauma in a group setting, during the sensitive 24-hour post-incident window, this may increase rather than decrease memory consolidation. I think this tactic is especially problematic if there is social pressure or overt prescriptive advice from professionals to do this, when the individual may not wish to talk about the trauma. This type of pressure may feel coercive rather than freely consensual, a dynamic which could be re-traumatizing.
In another recent study (http://www.ncbi.nlm.nih.gov/pubmed/20889142 ), sleep deprivation following exposure to upsetting visual stimuli was shown to reduce aspects of implicit memory consolidation. This is consistent with other evidence showing that sleeping facilitates learning, by helping to consolidate recently acquired memories.
In conclusion, I think it is useful to know some simple techniques which could reduce the harm which traumatic experience can immediately impose upon the brain's memory systems. Immediate distraction with an absorbing visual activity, such as tetris, could be helpful. Sleeping right away may not be helpful, and may actually increase consolidation of traumatic memory.
For consolidated symptoms of PTSD, and for longstanding troubling thoughts, memories, images, and emotions, etc. it is clear that therapeutic dialog can be very helpful, provided the setting is safe, non-pressured, comfortable, with a strong sense of trust. Such gentle dialog could begin the process of weakening the strong negative emotional grip that the traumatic experiences may have in daily life. The evidence mentioned above has to do with reducing the incidence of PTSD in the first place, through specific tactics to be undertaken immediately after the trauma.
We could infer, conversely, that engaging in distracting activities, such as video games, after doing an activity that you would want to remember vividly (such as studying, or some other pleasurable or meaningful event), could lessen retention of these positive experiences (so, you shouldn't distract yourself with an absorbing visual activity right after studying). Also, having a good sleep after a pleasurable event, or after studying, would be expected to make these experiences more permanent in your factual and emotional memory. So, it's important to be conscious of what you do, during, but also after, events of significance.