Figure 12.

Summary of the laminar organization of connectivity and unisensory/multisensory features of the LRSS. The laminar distribution of converging extrinsic connections from unisensory areas SI (left) and A1 (right) are represented by the array of light gray arrows that are scaled in proportion to their laminar termination in LRSS. The preference for external inputs to target the supragranular layers (>80% of terminals) corresponds with the higher density of dendritic spines there, presumably to accommodate the high number of excitatory inputs. Intrinsic, translaminar connections from of layer 2/3 neurons (small, dark gray arrows) relay signals to layer 5/infragranular layer neurons where extrinsic inputs are comparatively sparse. Given that unisensory and multisensory neurons are found in both the supra- and infragranular layers, and that the general output targets of cortex are identified as unisensory (black arrows labeled as somatosensory, auditory) or multisensory, suggests that unisensory and multisensory signals are processed in parallel as they course through the LRSS circuit. Dashed lines indicate laminar boundaries. S1=primary somatosensory cortex, A1=primary auditory cortex. Light gray arrows, extrinsic inputs; dark gray arrows, intrinsic connections, black arrows, outputs.