Shen-Ju Chou

Primary somatosensory cortex (S1) contains a map of the body that mirrors maps in hindbrain and thalamus. During development, peripheral changes alter the map in S1. Here the authors use a mouse mutation that alters S1 size and leads to plasticity in the S1 map that is transferred to the thalamic map. The primary somatosensory cortex (S1) contains a complete body map that mirrors the subcortical maps developed by peripheral sensory input projecting to the sensory hindbrain, the thalamus and then S1. Peripheral changes during development alter these maps through 'bottom-up' plasticity. Unknown is how S1 size influences map organization and whether an altered S1 map feeds back to affect subcortical maps. We show that the size of S1 in mice is significantly reduced by cortex-specific deletion of Pax6, resulting in a reduced body map and loss of body representations by an exclusion of later-differentiating sensory thalamocortical input. An initially normal sensory thalamus was repatterned to match the aberrant S1 map by apoptotic deletion of thalamic neurons representing body parts with axons excluded from S1. Deleted representations were rescued by altering competition between thalamocortical axons using sensory deprivation or increasing the size of S1. Thus, S1 size determined the resolution and completeness of body maps and engaged 'top-down' plasticity that repatterned the sensory thalamus to match S1.

We will focus on describing our recent studies on the laminar and area patterning of the mammalian neocortex. We describe a novel IgCAM, MDGA1, that is a unique laminar and area specific marker, and functional studies showing its influence on radial migration. We also describe time-lapse imaging studies showing that the preplate and its derivative, the subplate, is a cellular protomap of the cortical ventricular zone, and the implications of this finding for mechanisms of arealization and development of area-specific TCA projections. We will summarize studies of each of the four transcription factors, Emx2, Pax6, Couptf1 and Sp8, expressed by cortical progenitors and involved in specifying area patterning. Finally, we will describe studies showing that area size dictates performance at modality-specific behaviours.