WordNet (r) 3.0 (2006):

brain wave
    n 1: (neurophysiology) rapid fluctuations of voltage between
         parts of the cerebral cortex that are detectable with an
         electroencephalograph [syn: brainwave, brain wave,
         cortical potential]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "brain wave":
   automatic response, blind impulse, brainstorm, drive, fancy, flash,
   fleeting impulse, gut response, impulse, inspiration, instinct,
   involuntary impulse, natural impulse, notion, quick hunch, reflex,
   sudden thought, urge