Slurred speech is another commonly occurring symptom of a concussion. The doctors categorize slurred speech after a traumatic brain injury as dysarthria. A person experiences dysarthria when the regions of the brain that manage the muscles in use for speech suffer severe damage. A brain injury like a concussion can leave the muscles in your pharynx a lot weaker or even paralyze them. As a result, the people might know exactly what they are willing to say but find it hard to say those words in a clear voice.