Brain structures of echolocating and nonecholocating bats, derived in vivo from magnetic resonance images.

Magnetic resonance images of the brain of five species of wild bats, including three species of Microchiroptera, one species of echolocating Megachiroptera and one species of nonecholocating Megachiroptera, were obtained in vivo. The relative volumes of the inferior colliculus and the superior colliculus to the brainstem were derived from the magnetic resonance images and compared among different species. In general, the relative size of the inferior colliculus was much larger in Microchiropterans than in Megachiropterans, and in echolocating Megachiropterans than in nonecholocating Megachiropterans. The relative size of the superior colliculus was similar in these two suborders. Agreeing with the previous results and consistent with the current hypothesis that Megachiropterans originated from Microchiropterans, the results suggest that the inferior colliculus of Megachiropterans tends to degenerate during the process of evolution, as these fruit bats use more vision and smell than hearing when they forage. The results also demonstrate that magnetic resonance imaging can be used to study the neuroanatomy of wild bats noninvasively.