How was this achieved and do these scenes serve any purpose story-wise or meant as a simple mind trip to generate the feel of the movie?
Limitless even opens with such a seemingly endless zoom shot better know as Fractal zoom, though the scene you referred to, is not endless, but is more of a fly-by zoom shot. Such effects are often rendered by processing normal footage (using cameras) using advanced video editing software (like Adobe After Effects) or customized code to render fractal zoom.
This interview here discusses in detail about the technology, technique and idea behind that opening shot for Limitless.
The article referred to, above says this about the software used
Another example of a really long fractal zoom can be found here on YouTube. This video, took 6 months to render!