Complex sentence: There is much debate as to when people started looking at the functions of different organs, but for many centuries, the brain was looked upon as a useless organ and was generally discarded during burial processes and autopsies.
Split into simpler sentences: There is much debate as to when human societies started looking at the functions of different organs. For many centuries, the brain was looked upon as a useless organ and was discarded during burial processes and autopsies.