Biomedical Engineering Reference
In-Depth Information
has been shown to enhance responsiveness of primary visual cells
in the rat
(39)
. Given the distance between the illuminated lens
and the eyes (i.e.,
2.3 cm), we could then estimate the angle
in the visual field subtended by each stimulus. With reference to
an origin at the intersection of the sagittal midline, the coronal
interocular line, and the horizontal plane through the eyes, the
stimuli appear approximately at 35-50
◦
azimuth and 10-40
◦
ele-
vation relative to the horizontal meridian.
In addition to a spatially specific and robust stimulus deliv-
ery method, our goal was to control accurately both the inten-
sity (lux) and wavelength (color) of the stimuli. We opted for
light emitting diodes (LEDs; Luxeon Star III, Lumileds Lighting,
LLC, San Jose, CA), which come in a variety of colors (i.e., with
well defined emission spectra) including “white.” A power mod-
ule (LuxDrive BuckPuck, LEDdynamics, Randolph, VT, USA),
with a custom-made associated circuitry, was used to convert an
applied voltage to a constant current fed to the LEDs because
the output luminous intensity of LEDs is more linearly propor-
tional to current. The controlling input voltage was applied by
the CED unit using Spike2 software. We used acrylic collimator
lenses to target the wide-angle LED light into the optical cables,
which attached to cradles in front of the LEDs. The intensity of
light entering each cable could thus be independently adjusted.
Before each experiment, we calibrated the stimuli using a light
meter (Extech Instruments, Waltham, MA). We measured, at four
different pre-defined input voltages, the illuminance (in lux units)
emitted from the stimuli.
∼
The design of our whisker stimulator is based on accurate control
of airflow through solenoid valves, similar to the case of the olfac-
tory stimulator as discussed above. Aquarium air pumps were con-
nected to two computer-controlled valves, the outputs of which
were connected to long (
2.1.3. Whisker Stimulator
8 m) Teflon tubes that ran the length
of the imaging bore to the rat's whisker pad. Whiskers on the
chosen side(s) were trimmed to a length of
∼
20 mm. All non-
stimulated whiskers, including the non-selected whiskers on the
contralateral side, were trimmed away to avoid spurious activa-
tions. A lightweight masking tape (length and width of 20 and
6 mm, respectively) was fastened to the chosen whisker(s) to
increase resistance to airflow while at the same time ensuring iden-
tical motion of the selected whisker(s). By alternative opening and
closing of the solenoids, we generated short air puffs through the
tubes near the whiskers. The distance between the tubes and the
whiskers was typically about 2 cm. The default orientation of the
tubes moved the whiskers in a rostrocaudal direction, but dorsal-
ventral is also possible by changing the orientation of the tubes
relative to the whisker pad. Alternating air puffs at rates of up to
tens of Hz deflected the stimulated whiskers by
∼
∼
2 mm.
