Figure 2.

Experimental setup for measuring degree of lateral stimulus spread (spatial selectivity). (A) Schematic of setup. Studies were performed to demonstrate the capacity of the sMEA to activate a specific region of longitudinally oriented axonal bundles (spinal tracts) in the in vitro, isolated spinal cord of postnatal days 10–14 rats. Single-site sMEA stimuli were delivered to the surface of the cord (thoracic levels 6–8) and the evoked compound action potential (CAP) response was recorded on adjacent white matter tracts located 10–15 mm (approximately eight spinal segments) caudal to the site of activation. A rigid tungsten microelectrode stimulating the same longitudinal tract was used as a comparison. (B) Photograph of sMEA and tungsten electrode positions on cord surface. The sMEA was wrapped, exposures facing inward, around the spinal cord, and delivered bipolar stimuli between the second and third electrodes from the left. Dotted line shows alignment of bipolar stimulus locations for the two electrode types (sMEA and tungsten). (C) Photograph of in vitro setup showing recording location. White arrow points to glass suction recording electrode tip, which was moved in 50 μm lateral increments to measure CAPs evoked from the stationary sMEA and rigid tungsten electrodes. Bar on cord shows lateral range of recordings (>700 μm).