Checkout the work of Walter J. Freeman at UC Berkeley and G. Buzsaki
(I.m not sure where his group is , but I think his name is sufficently
rare to give you the page on a general web search!). Freeman deals
with the changes in the cortical EEG in response to perception,
whereas Buzsaki is concerned with the theta rhythms of the
hippocampus. Both sites have a large number of papers for free
download, so their references should give you ideas for wider
searching later on. Freeman has also published a few books which you
can get on Amazon.
Cheers