Biomedical Engineering Reference
In-Depth Information
impedance microelectrode and a fiberoptic laser Doppler probe
(50, 51)
. The microelectrode was glued to the side of an 18 G
spinal needle shaft (Terumo, Tokyo, Japan) and the bare laser
Doppler probe was placed inside the needle shaft so that tips of
each sensor protruded (approximately 1.5 mm) beyond the nee-
dle tip. The shaft of the needle was then placed in a microelec-
trode holder (Plastic One, Roanoke, VA) on the stereotaxic appa-
ratus, and the tip of the dual-probe was advanced into the rat
cortex (see below) to a depth corresponding to cortical layer 4,
which could later be verified by histology
(52)
. For all olfactory
bulb and visual recordings, only the microelectrode was used. The
coordinates for all neurophysiologic measurements were guided
by prior fMRI data
(16, 26)
.
Cerebral blood flow (CBF) was measured using a fiberop-
tic laser Doppler probe (830 nm; Oxford Optronix, Oxford, UK)
sensitive to red blood cell flux. The bare fiber laser Doppler probe
had a total diameter of less than 450
m. CBF was dynamically
recorded by the CED unit without any additional filtering. Elec-
trical activity was measured with tungsten matrix microelectrodes
consisting of two electrodes separated by 410
μ
μ
m (FHC, Bow-
doinham, ME) with high impedance (2-4 M
m).
The pre-amplified electrical signal was digitized with the CED
unit. The data were collected with a large bandwidth (10 Hz-
20 kHz) and filtered into local field potential (LFP; 10-150 Hz)
and multi unit activity (MUA; 300-1500 Hz) bands. The LFP
data were represented in the raw arbitrary units of mV. From the
MUA data, a template-matching algorithm (Spike2) was used to
detect action potentials fired by individual neurons near the elec-
trode tips to calculate spike rates (10 s bins) in units of Hz.
For recordings from somatosensory regions, tiny burr holes
above contralateral and ipsilateral areas [forelimb area (S1
FL
): 4.4
mm lateral and 1.0 mm anterior to bregma; whisker barrel field
(S1
BF
): 4.5-5.5 mm lateral 2.5-3 mm posterior to bregma] were
thinned and the skull was carefully opened. Recordings from the
visual areas were guided by locations from the Paxinos and Wat-
son atlas
(53)
. For recordings from the olfactory bulb, tiny burr
holes above the olfactory bulb were made
(
medial location: 0.5
mm lateral and 7.7 mm anterior from bregma; lateral location:
1.5 mm lateral and 8.7 mm anterior from bregma].
, tip size
<
1
μ
3. Results
3.1. Olfactory
Stimulation
We examined odorant-induced activity patterns in the olfactory
bulb with ester (isoamyl acetate) and aldehyde (hexanal) stimu-
lations given to both nostrils in the same subject (
Fig. 10.2)
.
None of the odorants or their concentrations examined caused
