Retired players Zach Thomas, Kyle Turley and Conrad Dobler also have said they'll help the Center for the Study of Traumatic Encephalopathy at Boston University School of Medicine.
The wife of Hall of Famer John Mackey pledged to donate his brain after his death. Mackey has dementia.
In December, the NFL and its players association said they would support the center's research and encourage players to participate. The NFL said it was willing to give $1 million or more to the center.
Current NFL players Sean Morey of the Cardinals, Matt Birk of the Ravens, and Lofa Tatupu of the Seahawks earlier had agreed to donate their brain for research.
"The only way we will truly understand the long-term effects of repetitive head trauma in football is to study a large group of athletes throughout their lives and then examine their brains following death," said Dr. Robert Stern, a co-director of the center.
The BU brain researchers have said they found links between repeated head trauma and brain damage in boxers, football players and a former NHL player - and the group has been critical of the NFL's stance on concussions.
NFL commissioner Roger Goodell met in October with a member of the center to discuss concussions and the BU project.
The NFL took several steps this season to ramp up its attention to concussions in the aftermath of a congressional hearing on the topic and as high-profile players such as Ben Roethlisberger, Kurt Warner, Clinton Portis and Brian Westbrook were sidelined by head injuries.
The league's steps included stricter return-to-play guidelines detailing what symptoms preclude someone from participating in games or practices; a mandate that each team select a league- and union-approved independent neurologist to be consulted when players get concussions; and the departure of the two co-chairmen of the NFL's committee on brain trauma.