The Galaran memory device is a device created by the Galarans from Goa'uld memory recall devices that were discovered on their planet. The device is capable of copying a persons memory into another person.
In 2006, Marell used the device to implant his memory of the murder of Reya Varrick into Lt. Colonel Cameron Mitchell and erase it from his own mind. However, the implantation was not perfect; by examining the memory of Reya's murder and comparing it to Mitchell's memory of a time he accidentally destroyed a civilian convey that was incorrectly identified as a military target, they were able to compare and contrast the false memory with a genuine example of a time Mitchell had been knowingly responsible for the deaths of innocent people (he had been informed of the real circumstances after firing the missiles but before they struck the convoy). Having determined that the memory of Reya's murder was fake, they subsequently examined the memory in greater detail and determined that Mitchell's brain was 'rebelling' against the sight of 'his' reflection in a mirror, allowing them to analyze the reflection and correct it accordingly. (SG1: "Collateral Damage")
Several months later, Mitchell used a modified version of the device to show Major Bryce Ferguson what he had been exposed to traveling through the Stargate, just hours before he died, due to Mitchell's guilt about his self-perceived role in the accident that led to Ferguson's death. (SG1: "Stronghold")