I feel like nasal sounds being associated with negation must be even older than PIE.
replyI've never heard of it being based on that root before. Do you have a source?
replyThe two big ones for discussing Germanic languages and their inheritance would probably be:
reply"From Proto-Indo-European to Proto-Germanic", Ringe.
And the simpler "Lexikon der indogermanischen Partikeln und Pronominalstämme", Dunkel.
Both use "n̥-s-ero-", though in the more traditional /ˈun.se.rɑz/ form.