Correlations between major brain regions in Chiroptera.

Unlike small homogeneous nuclei, progression indices of large heterogeneous brain regions show no negative correlations and give no evidence of compensatory effects, presumably because the evolutionary progressions and regressions of multiple neighboring functions mask each other. The diencephalon and various parts of the telencephalon show large positive correlations, apparently reflecting the general increase in size of the brain, relatively to body weight, from presumably primitive to advanced forms. The neocortex is strongly correlated with the striatum, a putative precursor, and with the diencephalon, but less strongly correlated with the cerebellum in Chiroptera than in Primates. The mesencephalon is moderately correlated with the medulla oblongata and cerebellum, but uncorrelated with all parts of the telencephalon except the paleocortex. The bulbus olfactorius is correlated with the septum, schizocortex and hippocampus, but these correlations may be due mostly to the progression of these four structures in Megachiroptera and their regression in insectivorous Microchiroptera, and may not imply major direct functional relationships.