These were not as rich as the IT-type axons because corticothalamic projections only weakly cross the midline. But maybe we will be able to make some useful study of the differences of these two thalamic inputs in the future. 20/24

We were also asked by the reviewers about the corticothalamic projections. Here we used some other mouse lines in L5B (PT-type projections, Sim1_KJ18_Cre) and L6 (CT-type projections, Ntsr1_GN220_Cre). 19/24

Again, we see that injections close to each other – low offset (in um) – are again pretty similar (7GHI, top). This is especially strong in frontal and sensory. But correlations across the midline were symmetrical/strong for frontal but not motor or sensory (7GHI, middle). 18/24

We made similar comparisons in striatum. These images of ipsi and contralateral frontal corticostriatal projections are quite pleasing to the eye. They are, as you might predict from cortex, the most symmetrical for more anterior projections. 16/24

We even subdivided medial and lateral parts of S1 (suggested by a reviewer) and you can see how they differently project to the contralateral entorhinal areas (5MNOPQ). This figure was fun to make. 15/24

The cortical comparison shows that frontal projections to the other side are stronger than motor which in turn is stronger than sensory (3E). But even more than the strength, we were able to compare each injection to nearby injections from different mice (3GHI, top). 11/24

Focus on 3 parts of cortex: anterior mouse brain (frontal), motor, and somatosensory areas. I tried to stick to a red/purple/blue color scheme for these areas through the paper. Here we show where the injection was, with the ipsilateral and contralateral cortex in detail. 7/24

This line is pretty well restricted to layer 5 and we have a library of injections all over the dorsal cortex. As you might expect in anatomy work, we try to show some good examples of well labeled axons in a few examples. 6/24