Taken from Wikipedia:

Degus entered the research spotlight due to their unique relationship with sugar and diabetes, but are also studied for a wide variety of other reasons. Neuroscientists at the Riken Institute in Tokyo, Japan, used degus for research into tool use in animals with good eye-and-paw coordination, in which they spontaneously learned to use a tiny rake to retrieve out-of-reach seeds.[27] Degus have also been found to spontaneously stack objects in order of decreasing size.[28] In both cases it is the first time these behaviours have been recorded in animals other than apes and birds.
Another interesting area of degu research is circadian rhythm function, i.e. the ability of the brain to tell what time of day it is. Degus have the ability to show both diurnal and nocturnal rhythms if the environment permits,[29] allowing a unique opportunity for study. Degus can take cues that do not relate to day length, such as temperature,[30] melatonin levels[31] and even scents from other degus[32] to adjust their rhythms.
Degus are also invaluable in development and aging studies. Research has shown that separation anxiety caused by separating pups from their mother from an early age for periods of half an hour or more can cause developmental and behavioural changes in later life, similar to ADHD in humans.[33] In elderly degus, neural markers have been discovered which are remarkably similar to those in humans with Alzheimer's disease,[34] which is the first time this has been seen in a non-human mammal.