Universal Soldier

In 1969, a U.S. Army Special Forces team receives orders to secure a village against North Vietnamese forces. Luc Deveraux (Jean-Claude Van Damme) discovers members of his squad and various villagers dead, all with their ears removed. Deveraux finds his leader Andrew Scott (Dolph Lundgren), who has gone insane, with a string of severed ears and holding a young boy and girl hostage. Devereaux, who is near the end of his tour of duty, tries to reason with Scott, who shoots the boy and orders Devereaux to shoot the girl to prove his loyalty. Deveraux refuses and tries to save the girl, but Scott kills her with a grenade. The two soldiers shoot each other to death. Deveraux and Scott's corpses are recovered by a second squad and cryo-genically frozen, their deaths covered up as "missing in action".
Deveraux and Scott are revived without memories of their previous lives and are selected for the "Universal Soldier" program, an elite counter terrorism unit, and are deployed via an Aero Spacelines Mini Guppy to the Hoover Dam to resolve a hostage situation. Devereaux used efficient means to dispatch terrorists, but Scott used excessive force, which causes concern among the project technicians. The team demonstrates their superior training and physical abilities against the terrorists, such as when GR76 (Ralf MÃ¶ller) withstands close-range rifle fire. After the area is secured, Devereaux begins to regain patches of memory from his former life upon seeing two hostages who strongly resemble the villagers he tried to save in Vietnam, causing him to ignore commands from the control team and become unresponsive.
In the mobile command center, it is revealed that the UniSols are genetically augmented soldiers with enhanced healing abilities and superior strength, but also have a tendency to overheat and shut down. They are given a neural serum to keep their minds susceptible and their previous memories suppressed. As a result of the glitch, Woodward (Leon Rippy), one of the technicians on the project, feels it may be better to remove Devereaux from the team until he can be further analyzed, but UniSol commander Colonel Perry (Ed O'Ross) refuses. TV journalist Veronica Roberts (Ally Walker), who was fired while covering the Hoover Dam incident, tries to get a story on the UniSol project in order to get her job back. Roberts sneaks onto the base with a cameraman, discovering GR76 immersed in ice, still alive despite normally-fatal injuries.
When her presence is noticed, Devereaux and Scott are ordered to capture her. She flees to her cameraman's car, but they crash. Scott coldly executes the cameraman against orders, before Devereaux stops him from shooting Roberts. Together, Devereaux and Roberts escape in a UniSol vehicle. Colonel Perry insists on preventing knowledge of the UniSols getting out, not only to the public, but to the Pentagon, which does not know the true nature of the project. Devereaux and Roberts flee to a motel, where Roberts discovers she has been framed for the murder of her cameraman. Scott's previously insane personality begins to emerge, causing him to kill Perry and the technicians. Scott then takes command of the UniSol team, ordering them to find and kill Devereaux and Roberts.
Devereaux continues to rebuild his memory while Roberts tries to find more information about the UniSol program. They meet Dr. Christopher Gregor (Jerry Orbach), the creator of the program, who informs them that the UniSol project was started in the 1960s in order to develop the perfect soldier. Although they were able to reanimate dead humans, they were never able to overcome the body's need for constant cooling. The other major problem is that memories of the last moments of life are greatly amplified. In Devereaux's case, he still believes he is a soldier who wants to go home, while Scott believes he is still in Vietnam fighting insurgents. When Devereaux and Roberts leave the doctor's office, they are caught and arrested by the police. En route to jail, the police convoy is ambushed by Scott and GR76. A chase ensues, ending when the police bus and the UniSol truck both drive off a cliff and explode, killing GR76. Devereaux and Roberts head to Devereaux's family's farm in Louisiana.
After Devereaux reunites with his family, Scott appears and takes the family and Roberts hostage. A brutal fight ensues, and Scott's use of muscle enhancers enables him to mercilessly beat Devereaux. Roberts manages to escape, only to be seemingly killed by a grenade thrown by Scott. Devereaux grabs the muscle enhancers Scott used and injects himself. Now evenly matched, Devereaux fights back and is able to impale Scott on the spikes of a hay harvester. Devereaux then starts the machine up, grinding Scott into pieces. Roberts survived the explosion and she and Devereaux embrace.
Alternate ending[edit]
The Special Edition DVD release features an alternative ending which starts shortly after Scott takes Deveraux's family and Roberts hostage. As Deveraux grabs a shotgun in the kitchen, the front door opens and he sees his mother before Scott shoots her to death. In the final fight between Deveraux and Scott, Deveraux does not use Scott's muscle enhancers. Shortly after grinding Scott to death, Deveraux is shot by his father before Dr. Christopher Gregor and his men appear.
Gregor explains that he used Deveraux to get both him and Scott, and that Deveraux was living with people posing as his parents. He then has his men shoot Deveraux, but before Deveraux dies, the police and Roberts' news crew arrive. The news crew douse Deveraux with a fire extinguisher to stabilize him while Dr. Gregor and his men are arrested. Roberts is given the microphone to cover the arrest, but she loses all composure while on the air, dropping the microphone to comfort Deveraux.
Several days later, Deveraux is reunited with his real parents. The film ends with a eulogy narrated by Roberts, who explains that Deveraux rejected all life-prolonging medications before dying a natural death.

Question: What causes Devereaux to regain patches of memory from his former life ?