Caretaker29, welcome to the forum. I think it all depends on what type of brain injury. And the age of the person. Some people, such as football players can receive brain concussions but it isn't until they are much older that they could develop memory issues.
My Mom was in her late 90's and was fairly sharp until she fell and had head trauma. That fall accelerated her into late stage dementia where she could no longer stand/walk, or understand what was going on around her.
My FIL fell and hit his head on cement steps. He suffered a head injury. He was in the hospital for several months. He seemed to recover completely but several years later he had dementia. We always thought it was a result of the fall.
My Mom was in her late 90's and was fairly sharp until she fell and had head trauma. That fall accelerated her into late stage dementia where she could no longer stand/walk, or understand what was going on around her.
https://www.alz.org/alzheimers-dementia/what-is-dementia/related_conditions/traumatic-brain-injury
My FIL fell and hit his head on cement steps. He suffered a head injury. He was in the hospital for several months. He seemed to recover completely but several years later he had dementia. We always thought it was a result of the fall.