Part Number: ADS1298R

Hello everyone:

I have a doubt, I see a filters (red rectangle) on page 62 from PDF and the values from resistor and capacitor give a Low-pass Filter which 153 and 339 KHZ (I think that this are antialiasing), but I don´t know why is neccesary to atenuate this frequencies.

I would appreciate to much if you want to explain me why is necessary use this resistor and capacitor values but no others, I am new on this field and I investigate a lot but I don´t get this information.

This information is avaliable on the Document "ADS1298RECG-FE ECG Front-End Performance Demonstration Kit", the link is this:

Pd. Sorry for my english, I started to learn in previous days.