What does it mean if you've been involved in some type of accident, you have a concussion, you have symptoms, but they ran an MRI on you and it came back normal? I get calls constantly from people who have been in that same situation where they've been to the emergency room and they ran a CT scan and an MRI of the brain and there were no findings. The person leaves the hospital thinking I must not have a brain injury but the fact that these tests are negative does not mean anything in terms of proving the existence of a brain injury.
Remember that the symptoms that you're feeling are the evidence of what's been damaged in your brain. The damage of the brain could be causing memory loss, headaches, speech issues and affecting many types of things in your life. The question then becomes how do you find it and prove where it actually exists.
An MRI many times is not specific enough to find the damage that has occurred in your particular situation. Either the test was done too soon and the damage hasn't shown itself within the brain or the damage such as those to the neurons is too small to be detected. The fact that you have had a negative MRI doesn't mean anything in terms of having a very serious brain injury.