Concerning the excitatory cells, I was referring to L5 PT and L6 CT cortical pyramidal cells that project to the thalamus, and to the miscalled thalamic “relay” cells (“miscalled” because they probably do more than a simple relay)
It seems that virtually all axons between the thalamus and the cortex give some collaterals in the TRN (which sends inhibitory inputs to thalamic relay cells and/or other inhibitory thalamic interneurons).
This illustration from Sherman’s video shows the different options:
Other illustrations from the same video:
I hope it helps. On my side, I don’t know much about the internal thalamic computations.