MAPPING FUNCTIONAL-ACTIVITY IN RODENT CORTEX USING OPTICAL INTRINSIC SIGNALS

We have investigated the dynamic response of rodent posteromedial barr el subfield (PMBSF) cortex to mechanical whisker deflection, using opt ical intrinsic signal imaging. While electrophysiologic response in ba rrel cortex has been well studied, dynamic metabolic changes affecting activity-related perfusion or oxidative enzymes are not well understo od. Male Sprague-Dawley rats were anesthetized. Contralateral single a nd multiple vibrissae were deflected while images of somatosensory cor tex were acquired with a charge-coupled-device camera. Intrinsic signa ls were observed over PMBSF as stimulus-related reflectance decreases (10(-3) of baseline) comprising two distinct spatiotemporal components , At 610 nm the first, diffuse, component begins 0.5-1 sec after stimu lus onset, peaks at 2.5-3 sec, and returns to baseline by 4-5 sec. The second component is macrovascular, beginning at 1-1.5 sec, peaking at 3 sec, and dissipating by 5-6 sec. Similar patterns were observed at 550 nm and 850 nm, Signal size and location varied with the stimulus, Evoked potentials were found to have maximal amplitude in the region o f maximal optical signals, diminishing toward the optical periphery. W e have demonstrated PMBSF response to vibrissal deflection using optic al reflectance methods. These intrinsic signals overlie regions of max imal electrophysiologic response, but commence, peak, and extinguish o ver a time scale of seconds from stimulus onset. They most likely indi cate activity-related microvascular recruitment and chromophore redox changes.