Contributions of mTBI to Neurodegeneration Due to Chronic Traumatic Encephalopathy (CTE) and Alzheimer's Disease (AD)

This study is investigating whether mild or moderate traumatic brain injuries (TBI, also known as concussions) contribute to brain degeneration similar to what is seen in Alzheimer's disease and chronic traumatic encephalopathy (CTE). Participants undergo brain scans and spinal fluid tests to look for early signs of neurodegeneration. **You may be eligible if...** - You have normal colour vision and visual acuity of at least 20/30 - You can demonstrate effort on memory tests - You have intact decision-making ability - You can safely have a lumbar puncture (spinal tap): no blood thinners, no bleeding disorders, no spinal infection, and normal blood clotting values - You fall into one of these groups: a history of mild TBI diagnosed by a physician; a history of moderate TBI; or mild cognitive impairment (MCI) without a history of TBI (control group) **You may NOT be eligible if...** - You are on blood thinners (such as warfarin) or antiplatelet medications (aspirin, Plavix) - You have a space-occupying lesion on MRI - You have a bleeding disorder or abnormal clotting values - You have an infection near the spine - You cannot demonstrate adequate effort on cognitive testing Talk to your doctor to see if this trial is right for you.