ONTOGENETIC DEVELOPMENT OF SOMATOSENSORY THALAMUS .1. MORPHOGENESIS

Structural maturation of the somatosensory thalamus in several laboratory mammals [rat, cat, primate and human] was studied by Golgi methods. The period covered extended from approximately 1 wk before term to 90 days after birth with emphasis on the immediate postnatal period. Although all systems appeared immature at birth, those ascending and descending axon systems playing upon the ventrobasal complex tended to mature more quickly than certain significant elements on the neuropil of the receptive field. Those elements were particularly the small dendritic structures (for example, excrescences, tufts, etc.) which enter into the formation of synaptic glomeruli and were probably involved in the dendrodendritic linkages which abound in this part of the thalamus. The possible significance of the earlier maturation of thalamopetal afferents compared to the intrinsic thalamic neuropil whose processing operations they modulate, was discussed.