Which rodent has the highest ratio of brain mass to body mass?

Beaver a large semiaquatic broad-tailed rodent that is native to North America and northern Eurasia. It is noted for its habit of gnawing through tree trunks to fell the trees in order to feed on the bark and build dams. Beaver has the highest ratio of brain mass to body weight among rodents, which is reflected in the behaviour and the ability to act not only instinctively, but also logically.