1 2 Differential Response Patterns in the SI Barrel and Septal 3 Compartments During Mechanical Whisker Stimulation

26 A growing body of evidence suggests that the barrel and septal regions in layer IV of rat primary 27 somatosensory (SI) cortex may represent separate processing channels. To assess this view, pairs of barrel 28 and septal neurons were recorded simultaneously in the anesthetized rat while a 4 x 4 array of 16 whiskers 29 was mechanically stimulated at 4, 8, 12, and 16 Hz. Compared to barrel neurons, regular-spiking septal 30 neurons displayed greater increases in response latencies as the frequency of whisker stimulation increased. 31 Cross-correlation analysis indicated that the incidence and strength of neuronal coordination varied with the 32 relative spatial configuration (within vs. across rows) and compartmental location (barrel vs. septa) of the 33 recorded neurons. Barrel and septal neurons were strongly coordinated if both neurons were in close 34 proximity and resided in the same row. Some barrel neurons were weakly coordinated, but only if they 35 resided in the same row. By contrast, the strength of coordination among pairs of septal neurons did not vary 36 with their spatial proximity or their spatial configuration within the arcs and rows of the barrel field. These 37 differential responses provide further support for the view that the barrel and septal regions represent the 38 cortical gateway for processing streams that encode specific aspects of the sensorimotor information 39 associated with whisking behavior. 40