在大腦皮質中，有一群神經細胞稱corticothalamic (CT) neurons，他們的特色是擁有很長的軸突(axons)伸到丘腦(thalamus)去。他們參與許多重要的生理功能，其中包括參與大腦的決策。
我們利用DiI染色的方法研究了出生前後時期CT neurons的型態。CT neurons是大腦皮質中較早形成的pyramidal cells。由胚胎時期第十八天(E18)到出生當天(P0)，細胞型態有顯著的改變：細胞體由光滑的卵形變為近似三角的形狀，且basilar dendrites形成；apical dendrite分支數目也明顯變多。同樣在此時期，大腦皮質最外緣的一層構造：the marginal zone (MZ)細胞組織排列也有明顯變化，分層結構由三層轉變為一層。而早在E18時期，CT neurons的apical dendrites就與位於MZ的細胞接觸。
CT neurons會形成突觸(synapses)，在E18時期即可以發現突觸小泡上的蛋白質synaptophysin會表現在apical dendrites上；而到了P0時期，synaptophysin也會分布在細胞體及鄰近的樹突(proximal dendrites)上。我們知道在E18時期大腦皮質與丘腦之間已形成雙向聯繫，我們發現此時接受GABA和glutamate訊號的突觸也已經在apical dendrites上形成了。因此我們認為至少在大鼠出生前三天，大腦皮質與丘腦之間已經有功能性的雙向傳遞。

The corticothalamic (CT) neurons, residing in the neocortex and sending axons to the thalamus, are important components for cortical processing and other brain functions. The morphology of DiI-back-labeled CT neurons in perinatal rat cortices was studied. The CT neurons are early-generated pyramidal cells in the neocortex. The CT neurons develop from cells having an oval cell body, no basilar dendrites and an apical dendrite with few branches in the marginal zone (MZ) into cells displaying a pyramidal-shaped cell body, 2-3 basilar dendrites and an apical dendrite with more complex branching in the MZ between embryonic day 18 (E18) and the day of birth (P0). The cellular organization of the MZ also indicates significant changes from a three-lamina pattern to a single-lamina one during the same period. The apical dendrites of the CT neurons can be found forming contacts with Cajal-Retzius (CR) and other cells in the MZ at E18. Synaptophysin-positive clusters mainly locate on the apical dendrites of E18, E20 and P0 CT neurons, while also are found on the cell bodies and proximal dendrites of P0 CT neurons. GABAergic and glutamatergic synapses are already formed on the apical dendrites of CT neurons as early as E18, when the cortical projection has reached their thalamic targets. Thus, it is likely that the cortex and thalamus in rat brains are linked to each other by functional connections in a two-way fashion at least three days before birth.

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