Comparing megaflops performed by the silicon hardware with symbolic operation by the human brain is comparing apples and oranges. If you measure the number of additions and multiplications performed by the neurons (yes, less precise but more fault tolerant) you will arrive at a much higher number of flops. Think about mental addition more like editing a spreadsheet cell. That includes lots of operation related to updating, display, IO, ... and the addition itself is an insignicant part of it. Same if you juggle number which actually represent anything in your head. The representing is the hard part. Not the arithmetic itself.

You can see the teraflops of the human brain at work if you consider the visual cortex where it is easy to compare and amp the image transforms to well known operations (at least for the first processing stages).