Af. Cannestra et al., REFRACTORY PERIODS OBSERVED BY INTRINSIC SIGNAL AND FLUORESCENT DYE IMAGING, Journal of neurophysiology, 80(3), 1998, pp. 1522-1532
All perfusion-based imaging modalities depend on the relationship betw
een neuronal and vascular activity. However, the relationship between
stimulus and response was never fully characterized. With the use of o
ptical imaging (intrinsic signals and intravascular fluorescent dyes)
during repetitive stimulation paradigms, we observed reduced responses
with temporally close stimuli. Cortical evoked potentials, however, d
id not produce the same reduced responsiveness. We therefore termed th
ese intervals of reduced responsiveness ''refractory periods.'' During
these refractory periods an ability to respond was retained, but at a
near 60% reduction in the initial magnitude. Although increasing the
initial stimulus duration lengthened the observed refractory periods,
significantly novel or temporally spaced stimuli overcame them. We obs
erved this phenomenon in both rodent and human subjects in somatosenso
ry and auditory cortices. These results have significant implications
for understanding the capacities, mechanisms, and distributions of neu
rovascular coupling and thereby possess relevance to all perfusion-dep
endent functional imaging techniques.