Dm. Rector et al., Scattered-light imaging in vivo tracks fast and slow processes of neurophysiological activation, NEUROIMAGE, 14(5), 2001, pp. 977-994
We imaged fast optical changes associated with evoked neural activation in
the dorsal brainstem of anesthetized rats, using a novel imaging device. Th
e imager consisted of a gradient-index (GRIN) lens, a microscope objective,
and a miniature charged-coupled device (CCD) video camera. We placed the p
robe in contact with tissue above cardiorespiratory areas of the nucleus of
the solitary tract and illuminated the tissue with 780-nm light through fl
exible fibers around the probe perimeter. The focus depth was adjusted by m
oving the camera and microscope objective relative to the fixed GRIN lens.
Back-scattered light images were relayed through the GRIN lens to the CCD c
amera. Video frames were digitized at 100 frames per second, along with tra
cheal pressure, arterial blood pressure, and electrocardiogram signals reco
rded at 1 kHz per channel. A macroelectrode placed under the GRIN lens reco
rded field potentials from the imaged area. Aortic, vagal, and superior lar
yngeal nerves were dissected free of surrounding tissue within the neck. Se
parate shocks to each dissected nerve elicited evoked electrical responses
and caused localized optical activity patterns. The optical response was mo
deled by four distinct temporal components corresponding to putative physic
al mechanisms underlying scattered light changes. Region-of-interest analys
is revealed image areas which were dominated by one or more of the differen
t time-course components, some of which were also optimally recorded at dif
ferent tissue depths. Two slow optical components appear to correspond to h
emodynamic responses to metabolic demand associated with activation. Two fa
st optical components paralleled electrical evoked responses. (C) 2001 Acad
emic Press.