Figure 3. Representative FP response depth profiles and corresponding CSD analyses before and after induction of LTP in a P4 (B) and P0 (C) rat. A, photograph of the 1 × 16-channel Michigan electrode array (left). Digital photomontage reconstructing the location of the DiI-covered electrode in coronal Nissl-stained section (right). B, C, Depth profiles of FP responses to single-whisker stimulation and corresponding CSD analyses in a P4 and P0 rat. The interelectrode distance was 100 μm in the P4 rat and 50 μm in the P0 rat. B1, C1, Control data obtained during baseline recording. B2, C2, Data after LTP induction. In CSD analyses, current sinks (blue) are downward-going and current sources (red) are upward-going. D, Relative FP slopes recorded in layer II/III and IV at P3–P5. E, Relative FP slopes recorded in the cortical plate and deep layer at P0–P1. Data are expressed as mean ± SEM. Box plots represent FP slopes during baseline and 35–60 min post-LTP induction (right). MZ, marginal zone; WM, white matter; SP, subplate; CP, cortical plate.