An 18-year-old man is involved in a motorcycle accident and sustains a closed head injury. After being in a coma for a few weeks, he awakens to find he has no memory of his family or life, and his cognitive function has declined to that of a 9- or 10-year-old child. His memories of his family and life never return, and he must re-learn how to perform activities of daily living. These findings are most consistent with: