Post-Concussive Diffuse Theta Slowing

A 19-year-old college football player presents to the sports-medicine clinic 5 days after a helmet-to-helmet collision with brief loss of consciousness and post-traumatic amnesia. He reports persistent headache, difficulty concentrating, photophobia, and poor sleep. Neurologic examination and non-contrast CT head are normal. A routine EEG is obtained to evaluate persistent post-concussive symptoms. The recording shows the pattern marked **A** in the diagram—a symmetric diffusely slowed background with dominant activity in the theta range (5–7 Hz) instead of the expected 9–10 Hz posterior alpha rhythm for his age. What does this EEG finding most likely represent?