A 50-year-old male with a 2-year history of cirrhosis underwent barium meal examination one year ago, revealing worm-eaten filling defects in the lower esophagus. Two days ago, he experienced melena, followed by somnolence and nighttime restlessness, prompting emergency admission. Physical examination showed flapping tremors. Laboratory tests revealed elevated blood ammonia. The most likely mechanism by which ammonia causes central nervous system dysfunction is: