This research study is designed to investigate the effects of a simple cognitive task (a memory reactivation cue following by playing the computer game "Tetris") on flashbacks and other post-traumatic stress symptoms after a road traffic accident. Patients presenting to a hospital emergency department soon after a road traffic accident will be randomly allocated to either the simple cognitive task intervention or usual care. Participants will be followed up at one week and one month. It is predicted that participants given the simple cognitive task intervention will develop fewer flashbacks and less severe clinical symptoms than those who are not. This will inform the potential future development of a simple technique to prevent distressing psychological symptoms after a traumatic event.

Inclusion Criteria:

• Aged 18 or over
• Experienced or witnessed a road traffic accident (as a driver, passenger, motorcyclist, cyclist or pedestrian)
• Met the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) criterion A1 for Post-Traumatic Stress Disorder (PTSD) ("experienced, witnessed, or confronted with actual or threatened death or serious injury)
• Can be seen in the emergency department within 6 hours of leaving the scene of the accident
• Report memory of the accident
• Fluent in written and spoken English
• Alert and orientated, Glasgow Coma Scale score (GCS) = 15
• Have sufficient physical mobility to play a computer game on the intervention platform (a Nintendo DS) at the point of taking informed consent
• Willing and able to provide informed consent and complete study procedures
• Willing and able to be contacted following discharge to complete follow-up assessments

Exclusion Criteria:

• Loss of consciousness of > 5 minutes
• Current intoxication
• Report a history of severe mental illness
• Current substance abuse or neurological condition
• Currently suicidal