They separated out those with mild injury, involving loss of consciousness or amnesia for less than 30 minutes with no skull fracture, moderate injury with loss of consciousness or amnesia for more than 30 minutes but less than 24 hours, or a skull fracture, and severe injury with loss of consciousness or amnesia for 24 or more hours. The scientists then tested volunteers to see which of the veterans had Alzheimer's. The risk of Alzheimer's and other forms of dementia was doubled in the men with moderate head injury, and it was four times greater in those who had severe head injury. Havlik said inflammation could be involved. Pathologists are seeing these within a few days or weeks of head injury.
Scientists believe the amyloid plaques are evidence of the brain trying to repair itself.
When brain cells are damaged, they send out many different chemical signals. For unknown reasons, some of these signals cause surrounding healthy brain cells to die. Havlik said the study got around earlier problems of previous studies, which showed that people could not remember head injuries they got decades ago, or which were based on interviews with family members. But he said other, unknown factors may have had a role to play. Copyright 2000 Reuters .