Skull of LB1 (Homo floresiensis) and modern human.
A few links and papers on Homo floresiensis brain size and the evolution of primate brain size. It seems that the evolution of brain size in primates is not one directional (always leading to larger brain) but instead body size and brain size is subjected to separate selective pressure. In the evolution of Homo floresiensis, evolution shrunk its brain size much like how evolution shrunk the brain size of Mouse Lemur, Marmosets and Mangabeys. So, the small brain size in Homo floresiensis is not pathological but instead a product of evolution. There's a good write up at A Primate of Modern Aspect.
A White-collared Mangabay (Cercobebus torquatus)
A Pygmy Mouse Lemur (Microcebus myoxinus). Smallest primate in the world. Photo from National Geographic.
A Pygmy Marmoset (Callithrix pygmaea). Photo from Wikipedia.
Links to paper and articles:
Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis (Montgomery et al, 2010)
Scientific American: What the small-brained hobbit reveals about primate evolution.
EurekAlert!: Is the Hobbit's brain unfeasibly small?
EurekAlert!: Does evolution always lead to bigger brains?
Wired Science: Evolution Shrank Some Primates’ Brains.