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.