Figure 9.

Cortical and laminar network organization of the AC. Left face of cube shows inputs from the ventral (MGv) and medial divisions (MGm) of the geniculate body and cortical areas and a schematic of the interlaminar connections; right face displays the pyramidal neurons of each layer and gives their axonal targets. Note that this schematic drawing illustrates only the major pyramidal neurons. Lemniscal thalamic inputs from MGv mainly arrive at layers III and IV, but also at layer VI. Nonlemniscal inputs from MGm activate layers I, Vb, and VIa. Thalamic activation of layer IV initiates a flow of information into the supragranular layers I–III and then down to the infragranular layers V and VI. Corticocortical inputs from the ipsilateral hemisphere (Ctx_i) terminate in the middle layers III and IV. Commissural inputs (Ctx_c) are widely distributed and arrive in almost all layers (II–VI). Inputs from the claustrum terminate in layer VI, whereas the entorhinal cortex (EC) and frontal cortex (FC) projects to neurons in layers (I) II, III, and V. Pyramidal cells are present in all layers, but layer I. The pyramidal axons of layers II–VI extend into layer I, with the exception of different pyramidal cell types in layers VIa and VIb. Corticocortical projections emerge from layers III, V, and VI. Feed-back to the auditory thalamus originates primarily in layer VI, but also in layer V, which also projects to the inferior colliculus (IC). Adapted from Mitani et al. (1985), Insausti et al. (1997), Linden and Schreiner (2003), Mitchell and Macklis (2005), Thomson and Lamy (2007) and Izhikevich and Edelman (2008).