He pressed and released the throttle on corners over and over to maintain speed. Read more here: https://www.paradigmshiftracing.com/racing-basics/analyzing-the-f1-greats-ayrton-sennas-throttle-technique#:~:text=As%20Senna%20increases%20throttle%2C%20he's,begin%20the%20process%20over%20again.