A positronic brain contained a neural net. The positronic brain required a lot of artificial synapse jumping. The Doctor said this made them "tricky to untangle".
Because positronic brains were closed systems, they were less venerable to corruption. This was a fact that saved Data from having his mind rewritten by the Tigan Edic in 2364. (TNG - The Space Between comic: "History Lesson")
Dr. Julian Bashir implanted Bareil Antos with a positronic matrix to keep him alive after part of his brain stopped functioning. Bareil awoke but said that the sensations he was experiencing did not seem real and seemed like a distant memory. Later, when other parts of Bareil's brain stopped functioning, Bashir chose to let Bareil die rather than replace the rest of his brain with positronic implants. (DS9 episode: "Life Support")