Somatotopic organization and cortical projections of the ventrobasal complex of the flying fox: an "inverted" wing representation in the thalamus

The present study investigates the somatotopic representation in the somato sensory thalamus of a megachiropteran bat. Using standard microelectrode ma pping techniques, representational maps were generated for the ventrobasal (Vb) and posterior (Po) thalamic complexes of the Grey-headed flying fox. A natomical tracing from neocortical injections provided additional data conf irming the somatotopy found physiologically. A full representation of the b ody surface innervated by the trigeminal and spinal nerves was found. Howev er, in contrast with other mammals, the representations of the forelimb and adjacent thoracic trunk within the thalamus were inverted. This means that the distal portions of the wing membrane and the tips of the digits were r epresented dorsally in Vb, and the thoracic trunk was represented ventrally In Po the digit tips were represented in the ventral most portion and the thoracic trunk in the dorsal portion of the nucleus. These results are disc ussed in relation to similarities of megachiropteran somatosensory thalamic nuclei to those of other mammalian species and in relation to the formatio n of thalamic somatotopic maps and fiber sorting.