You aren't really "sending data" though. Each one of the neruons just ends up triggering a circuit. And some of the fire signals are actually inhibitory signals to stop other neurons from firing. Not to mention all of the chemical signaling going on and the different types of patterns/behaviors that get activated through repetitive or limited activity.

So really to calculate bandwidth is kind of pointless. One the neurons use more dimensions than just on and off electrical signals as their state and two, neurons don't really pass information along when you think about it they just trigger circuitry.