A variant of the mammalian somatotopic map in a bat

Abstract

Two ordered representations of the body surface, S-I and S-II, have been described on the cortical surface of the brains of a variety of mammals; additional separate topographical maps have been found in the somatosensory cortex of the cat and monkey^1–5. Except for minor variations in the placement of the body parts, the basic somatotopy of the maps is remarkably consistent across species⁵. As the reasons for this consistency and the minor variations are unclear, we examined the somatotopy of the bat, whose body plan has been modified extensively so that the forelimb can be used for flight⁶. We report here that in both S-I and S-II of the grey-headed flying fox, not only is the representation of the distal forelimb displaced from its usual position on the map, but the digits are directed caudally instead of rostrally as they are in all other mammals studied. The variant somatotopy appears to reflect the postural differences between flying and walking mammals, supporting the notion that topographical maps may have functional significance apart from their point-to-point connections with the sensory periphery.