GLOBAL FORM AND SINGULARITY - MODELING THE BLIND SPOTS ROLE IN LATERAL GENICULATE MORPHOGENESIS

Optic nerve terminals segregate by functional class into distinct laye rs in the lateral geniculate nucleus, the thalamic relay nucleus of th e visual system. In the rhesus monkey, the number of geniculate layers changes abruptly from six posteriorly (central vision) to four anteri orly (peripheral vision). The plane of transition between these patter ns passes through small laminar gaps corresponding to the perceptual b lind spot caused by the exit of the optic nerve from the eyeball. Howe ver, this plane of transition has no apparent functional link to the b lind spot. A thermodynamic model of geniculate morphogenesis supports the hypothesis that the blind spot traps the transition in its stereot ypic position by introducing a singularity in an otherwise smooth grad ient in forces guiding the development of geniculate morphogenesis. Th is relation suggests that small-scale anomalies may be important in th e determination of large-scale patterns in biological structure.