Figure 9.
Frontal cortex (M2) excites the output layers of vM1. A–G, Quantification of inputs to vM1 from M2. A, AAV injection site in M2, 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 a single peak in deep layers (L5B and L6). D, Comparison of input strength across neurons in different cortical layers. Each point represents input to a pair of neurons in the same slice. 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 (L5B). 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. Note points above the pia are plotted as zero.