(A) An example experiment (BS265) in which ChR2 was expressed in VPM of a PV-Cre mouse crossed with a LSL-tdTomato report mouse, and whole-cell recordings were obtained sequentially neurons across different cortical layers in wS1. In the example experiment recordings were made from 7 PV-expressing inhibitory neurons (red), 2 PV-expressing L5 pyramidal neurons (#13 and #14, pink), and 10 non-tdTomato-expressing excitatory neurons (black). Neurons were filled with biocytin and post hoc stained with streptavidin conjugated to Alexa 647 to reveal dendritic morphology, which was digitally reconstructed. Neurons #6 (Exc L4), #7 (Exc L4), #9 (PV L4) and #10 (PV L5A) received the largest mean EPSPs in response to optogenetic stimulation of VPM (right). (B) The laminar location was assigned for each recording. The peak amplitude of the evoked EPSP averaged across trials was determined for each cell, and plotted for each layer along with the median (box plot, including interquartile range and whiskers) and the mean (filled circle, along with SD error bars) (left). The EPSP amplitudes from individual slices were normalized to the mean amplitude of the EPSP measured in the L4 EXC neurons of the same slice (center left). The slope of the rising phase of the EPSP was determined and plotted for each cell across layers (center right). The normalized EPSP slope was calculated by dividing by the mean slope of the EPSPs in the L4 EXC neurons recorded in the same slice (right).