Prenatal development of the human lateral geniculate nucleus.

The development of the human lateral geniculate nucleus has been studied on Nissl- and silver-stained sections from 61 fetal human brains collected during normal autopsy procedure. The age of the fetuses, which ranged from 16 to 40 (newborn) weeks was determined by comparing crown-to-rump lengths and body weights to the values published by Streeter ('20). The development of the human lateral geniculate nucleus is remarkably similar to that described for the rhesus monkey (Rakic, '77). As a result of the late growth of the pulvinar, the human lateral geniculate nucleus is displaced and rotated such that, at around week 24, the nucleus had come to lie along the ventrolateral border of the thalamus. The cellular laminae that characterize the adult nucleus are formed over a 3-week period of time beginning around the 22nd week of gestation. More caudal parts of the nucleus laminate first. During this same period of time, the optic disc representation in laminae 4 and 6 is also formed. Throughout most of the development of the human lateral geniculate nucleus, individual rows of cells can be seen extending across the nucleus. Although such rows of cells are best seen before the nucleus laminates, in older laminated nuclei the rows of cells are oriented either perpendicular or oblique, but never parallel, to the plane of the laminae. Previous findings in both the monkey (Rakic, '77) and human (Hickey and Guillery, '79) suggest it is possible that these rows of cells can be used to define the lines of projection through the nucleus. Incoming optic tract fibers run along, rather than perpendicular to, these rows of cells.