hide
Free keywords:
barrel cortex; layer 2/3; voltage-sensitive dye; imaging; in vivo; sensory response
Abstract:
The spatiotemporal dynamics of the sensory response in layer 2/3 of primary somatosensory cortex evoked by a single brief whisker deflection was investigated by simultaneous voltage−sensitive dye (VSD) imaging and whole−cell (WC) voltage recordings in the anesthetized rat combined with reconstructions of dendritic and axonal arbors of L2/3 pyramids. Single and dual WC recordings from pyramidal cells indicated a strong correlation between the local VSD population response and the simultaneously measured subthreshold postsynaptic potential changes in both amplitude and time course. The earliest VSD response was detected 10−12 msec after whisker deflection centered above the barrel isomorphic to the stimulated principal whisker. It was restricted horizontally to the size of a single barrel−column coextensive with the dendritic arbor of barrel−column−related pyramids in L2/3. The horizontal spread of excitation remained confined to a single barrel−column with weak whisker deflection. With intermediate deflections, excitation spread into adjacent barrel−columns, propagating twofold more rapidly along the rows of the barrel field than across the arcs, consistent with the preferred axonal arborizations in L2/3 of reconstructed pyramidal neurons. Finally, larger whisker deflections evoked excitation spreading over the entire barrel field within ˜50 msec before subsiding over the next ˜250 msec. Thus the subthreshold cortical map representing a whisker deflection is dynamic on the millisecond time scale and strongly depends on stimulus strength. The sequential spatiotemporal activation of the excitatory neuronal network in L2/3 by a simple sensory stimulus can thus be accounted for primarily by the columnar restriction of L4 to L2/3 excitatory connections and the axonal field of barrel−related pyramids
