Pro Football Hall of Famer Mike Haynes and current Chicago Bears linebacker Hunter Hillenmeyer are among more than a dozen NFL players who have pledged to donate their brain and spinal cord tissue for concussion research.

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 also pledged to donate his brain after his death. Mackey has dementia.

The NFL and its players association have said they will support the centre's research and encourage players to participate.