Figure 7.
Inputs to vM1 from motor thalamus. A, AAV injection site in anterior thalamus, after Paxinos and Franklin (2004). B, Fluorescence image of a coronal vM1 section (thickness, 300 μm) showing axonal fluorescence. Dashed lines mark region used for fluorescence quantification. C, Quantification of fluorescence as a function of laminar depth. Cortical depth is shown in fractional coordinates (pia, 0; white matter, 1); fluorescence was background subtracted and normalized. Dashed lines indicate borders of cortical layers. Note peaks in L1, L5A, and L5B, as well as a peak near white matter. D, Comparison of input strength across neurons in different cortical layers. Each point represents input to a pair of neurons in the same slice (solid circles, neuron pairs in which one cell had no detectable input). Dashed line represents unity. N, Number of pairs; p value, Wilcoxon signed rank test. E, Geometric means of the amplitude ratio, normalized to the layer receiving the strongest input (L5A). The overlaid graph shows the mean ratio and SD (bootstrap). F, Left, input maps for pyramidal neurons grouped by layer. Each column represents a single neuron, with its map compressed to a vector by summing across map locations at the same laminar depth. Thick white line, Laminar depth of the cell body. Vertical white lines, Boundaries separating layers. Color map adjusted to saturate top 0.5% of pixels. Right, Same neurons presented with input for each cell normalized its maximum input. G, Description of input location for pyramidal neurons for all four layers. Normalized mean input maps for each pyramidal neuron layer were averaged into a vector and aligned to the soma. These were then plotted as an input vector (left) and a graph (right), showing the input as a function of laminar depth relative to the soma in 50 μm bins. Triangles and dashed lines indicate soma depth. Only the strongest recipient layers (L2/3, L5A, and L5B) are plotted at right. Note points above the pia are plotted as zero.