The somatosensory cortex of the blind mole rat, Spalax ehrenbergi: An electrophysiological investigation

The blind mole rat, Spalax ehrenbergi, is a fossorial rodent with atrophied eyes covered with skin and fur. There seems to be no visual representation at cortical levels. The aim of the present investigation was to delineate the somatosensory cortex with special reference to a possible extension into the occipital (visual) area. In anesthetized animals the cortical surface was exposed and explored for surface field potentials or intracortical multiunit activity evoked by air puffs directed to small areas of the skin. Special attention was given to the borders of the head and body representation. Altogether the representation of the head and of various parts of the body is very similar to that found in other rodents. This includes a very large representation of the head. The somatosensory area encompasses large portions of the dorsal and dorsolateral surface, sparing, aside from a medial band of about 2 mm, an area frontal to the limb representation (presumably motor cortex) and a strip of 2-3 mm at the occipital region. This strip caudal to the somatosensory area was explored for visual responses with a photoflash and for auditory responses with an acoustic click, however, no reponses to these stimuli were encountered. Responses to acoustic stimulation were recorded caudolateral to the somatosensory area, which is similar to the location of the auditory cortex in the rat. This investigation shows that the somatosensory area reaches far into the occipital cortex in the mole rat and that no other sensory modalities are represented in the occipital region.