Sensorimotor corticocortical projections from rat barrel cortex have an anisotropic organization that facilitates integration of inputs from whiskers in the same row

Abstract

We used a dual anterograde-tracing paradigm to characterize the organization of corticocortical projections from primary somatosensory (SI) barrel cortex. In one group of rats, biotinylated dextran amine (BDA) and Fluoro-Ruby (FR) were injected into separate barrel columns that occupied the same row of barrel cortex; in the other group, the tracers were deposited into barrel columns residing in different rows. The labeled corticocortical terminals in the primary motor (MI) and secondary somatosensory (SII) cortices were plotted, and digital reconstructions of these plots were quantitatively analyzed. In all cases, labeled projections from focal tracer deposits in SI barrel cortex terminated in elongated, row-like strips of cortex that corresponded to the whisker representations of the MI or SII cortical areas. When both tracers were injected into separate parts of the same SI barrel row, FR- and BDA-labeled terminals tended to merge into a single strip of labeled MI or SII cortex. By comparison, when the tracers were placed in different SI barrel rows, both MI and SII contained at least two row-like FR- and BDA-labeled strips that formed mirror image representations of the SI injection sites. Quantitative analysis of these labeling patterns revealed three major findings. First, labeled overlap in SII was significantly greater for projections from the same barrel row than for projections from different barrel rows. Second, in the infragranular layers of MI but not in the supragranular layers, labeled overlap was significantly higher for projections from the same SI barrel row. Finally, in all layers of SII and in the infragranular layers of MI, the amount of labeled overlap was proportional to the proximity of the tracer injection sites. These results indicate that SI projections to MI and SII have an anisotropic organization that facilitates the integration of sensory information received from neighboring barrels that represent whiskers in the same row.

Current Flow in Vibrissa Motor Cortex Can Phase-Lock With Exploratory Rhythmic Whisking in Rat

“…2B and 5B). The presence of a motor signal in S1 cortex is certainly consistent with the known topographic connections between vibrissa M1 and S1 cortices (Deschenes et al 1998;Hoffer et al 2003;Izraeli and Porter 1995;Keller et al 1996;Kim and Ebner 1999;Veinante and Deschenes 2003). However, it appears inconsistent with the findings of Fee et al (1997), in which spiking by S1 units in phase with the fast, cycle-by-cycle motion of the vibrissae was largely extinguished on a unilateral lidocaine block of transmission along the contralateral facial nerve.…”

“…First, there are extensive intercortical projections from S1 to M1 cortices (Hoffer et al 2003;Izraeli and Porter 1995;Keller et al 1996;Kim and Ebner 1999). These maintain the topography of the vibrissa organization, with the majority of axons originating in layer 5 of S1 cortex and terminating in superficial layers of M1 cortex (Izraeli and Porter 1995).…”

Cellular mechanisms of motor control in the vibrissal system

“…VMC is the most intensely investigated vibrissal motor structure. Recent work clarified the localization [41,46], subdivisions [48], cytoarchitectonics [41], and connectivity of VMC [52][53][54][55]. Single-cell stimulation experiments in VMC allow for determining the cellular basis of cortical motor control with unprecedented precision [20].…”

“…A recent anatomical study [53] demonstrated that S1 inputs from vibrissa rows converge in VMC. VMC, in turn, projects selectively to septal columns of barrel cortex [54].…”

Early postnatal alcohol exposure reduced the size of vibrissal barrel field in rat somatosensory cortex (SI) but did not disrupt barrel field organization

“…Cortical barrels within the PMBSF receive one-to-one input from specific vibrissae on the contralateral face and provide the major somatosensory input for the rodent to navigate through its environment (Welker and Woolsey, 1974). Output from barrel columns project, in part, to motor cortex where it serves to modulate motor output (Hoffer et al, 2003). Barrel size depends on thalamocortical input and a smaller barrel field and barrels reported here likely reflect diminished cortical sensitivity and reduced sensory feedback to motor cortex.…”