Diagrams of axonal tracing paradigm and connections of rat brain somatosensory cortex.

<p>(A) Schematic diagram showing the principles of anterograde axonal tracing. Following injection of an anterograde axonal tracer to a brain region (I), the tracer is taken up by neurons (red dot in region I) within the injection site, and anterogradely transported along efferent axons, yielding distinctly labeled axons and terminal fields (solid lines) in regions (II, III) receiving axonal projections from the injected region. While the tracer <i>Phaseolus vulgaris</i> leucoagglutinin only gives anterograde labeling (solid red lines), the bidirectional tracer biotinylated dextran amine, also gives rise to retrograde labeling of neurons (red dot in region II), as well as secondary anterograde labeling of collateral axons (dashed red lines to regions II and IV). (B) Diagram of the rat brain showing axonal projections from the primary somatosensory cortex to well-known ipsilateral (solid red lines) and contralateral (dashed red lines) subcortical targets. (C) Schematic wiring diagram (modified from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022669#pone.0022669-Welker1" target="_blank">[31]</a>) showing the input and output relationships of the primary somatosensory cortex (SI). SI input from the trigeminal system is shown (solid black lines). SI output connections (solid red lines) reach several cortical and subcortical regions. Grey shading indicates regions investigated in the present study (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022669#pone-0022669-g005" target="_blank">Fig. 5</a>). CP, caudate putamen; Cb, cerebellum; MI, primary motor cortex; PN, pontine nuclei; Po, posterior complex thalamus, PR, perirhinal cortex; Rt, reticular nucleus thalamus; SI, primary somatosensory cortex; SII, secondary somatosensory cortex; SC, superior colliculus; TN, trigeminal nuclei; VB, ventrobasal complex thalamus.