Cuore di Vetro is one of my favourite Gelato place, it is located in Berlin near Rosa-Luxemburg Platz. Another great Gelato place in the world is Gelato Blue in Newton, Sydney, Australia, it is the only vegan ice-cream I know of which is on par with normal ice-cream, and this one is so good it is on par with Gelato in Italy.
A link to the paper: https://www.jneurosci.org/content/30/16/5498.short
The temporal discount factor, d, which they find is hyperbolic, i.e., of the form d = 1/(1 + k T), where k is some constant and T is the time to reward.