THE DEVELOPMENT OF THE SOMATOSENSORY REPRESENTATION IN THE SUPERIOR COLLICULUS OF VISUALLY DEPRIVED MICE

Mice were enucleated bilaterally at birth in order to investigate whether early visual deprivation had any influence on the development of the somatosensory representation in the superior colliculus (SC). Single unit recordings were performed during the 2nd, 3rd, 5th and 8th postnatal week in both normal and enucleated mice. It was found that, in visually deprived mice, there was a dramatic increase of the SC somatosensory units starting from the 3rd postnatal week, as occurs in normal mice. During the 5th and 8th postnatal week, this increase was larger than in normal mice, mainly due to the invasion of the somatosensory input into the superficial layers. In visually deprived mice, both the orientation of the somatosensory map and the magnification of some body parts, such as the upper vibrissae, did not show any difference with respect to normal mice. These results indicate the involvement of both vision-dependent and independent mechanisms in the formation of the SC somatosensory representation. In fact, whereas the segregation of the somatosensory afferents in the deep layers depended on the presence of visual input, the postnatal emergence and the topographic arrangement of the somatosensory map resulted to be independent of vision.