Hi another dave b
They're integrated into the brake levers!
Called Shimano STI Levers.
The way they work is this:
On this bike you have "Sora" gearing, they use a small button on the inside of the brake hoods to shift from a big cog to a smaller one. To move from a small cog to a bigger one you push the whole gear lever inwards towards the centre of the bike. The RH lever controls the rear gears, the LH lever contols the front.
Campagnolo uses the same button and lever system as Shimano Sora.
Higher Shimano systems use a small lever behind the brake lever to shift to a smaller cog instead of the thumb button on Sora and Campagnolo.
It takes a little getting used to but it allows shifting without taking your hands off the hoods or drops.
The only real downside is the added complexity over the old down-tube shifters or other kinds of thumb-shifters, but they're pretty damn reliable.