Figure 4. Challenges correlating electrophysiology and histology.

a–b) Average (a) and individual (b) depths of cortical layer IV, in mouse V1, where 0 represents the depth of layer IV on the day of insertion. Cortical layers drift along implants even when they are rigidly fixed to the skull. Therefore, it is not possible to correlate tissue sections to corresponding recording sites simply by tissue section depth. c) Linear silicon array next to coronal section of V1m (NeuN = green, Iba1 = red, Hoechst = blue, IgG = white). Histological cortical layers can be identified by the morphology and density of neurons. d) Current source density following presentation of visual stimulus (drifting grating) can be used to identify electrophysiological cortical layers. Current sinks are observed in L4, followed by L2/3, then L5, and then CA1. Representative CSD was recorded from isoflurane anesthetized mouse. (c) and (d) can be used to correlate histological outcomes to corresponding electrophysiological performance at the endpoint. Reprinted from⁸, Copyright 2015, with permission from Elsevier.