Biomedical Engineering Reference
In-Depth Information
written scripts running in the Spike2 environment (Cambridge
Electronic Design, Cambridge, UK) on standard personal com-
puters. All wires, pipes, and optical fibers needed to deliver the
stimuli to the rodent were led into the magnetically shielded scan-
ner room through small access holes in the sidewall. Exactly the
same stimulus delivery mechanisms were applied to the rodents
outside the magnet for bench neurophysiologic studies. All of the
stimulation devices described below were home-built.
2.1. Stimulation
Devices
The design of the olfactometer is based on John Kauer's original
idea
(35)
. We follow the design implemented in Lawrence
Cohen's laboratory
(36)
but with specific modifications neces-
sitated by the long delivery conduits needed between odorant
source (outside the magnet room) and the subject (inside the
magnet). Our olfactometer was designed and built to control
the delivery of odorants mixed in air provided by an aquarium
air pump. A schematic of the design is shown in
Fig. 10.1
.
A charcoal filter was used to remove odorants present in room
air before entering a system of solenoid valves (2 inlets and 1
outlet; Cole-Parmer Instrument, Vernon Hills, IL) and acrylic
flow meters (maintained at 1 L/min; Cole-Parmer Instrument).
The output of the flow meters was connected to long (
2.1.1. Olfactory
Stimulator
8m)
Teflon tubes that were led into the scanner room and then
connected to a glass tube placed in front of the rat lying inside
the magnet bore. The state of each solenoid valve (open/closed)
was switched using a relay circuit controlled by the CED unit
using Spike2 software. To provide a continuous steady-state envi-
ronment to the nasal mucosa, the applied airflow was humidified
and preheated to 28-30
◦
C.
The olfactometer operates as follows: Filtered air enters the
first solenoid valve (S1, always open except during the odor deliv-
ery) and the connected flow meter (FM) delivers that air to the
freely breathing rat. The filtered air stream also enters a glass bot-
tle with a specific odorant, from which the output is led through
the second solenoid valve (S2). The input to a third solenoid valve
(S3) is connected to a vacuum pump. During odorant stimula-
tion, S2 is opened for a defined duration, causing a constant flow
of the odorant, mixed in air, to be delivered into the glass tube
in front of the rat. To rapidly end the stimulus, S3 is opened for
a short period of time causing a transient vacuum in the delivery
tube and thus sucking out all remaining molecules of the odorant.
Each solenoid valve was switched in less than 50 ms. A straightfor-
ward extension to the system described above is one with multiple
odorant containers, solenoid valves, and flow meters arranged in
parallel to allow mixtures of odorants to be presented.
∼
The implemented design of the visual stimulus delivery system
resulted from iterative modifications with the primary goal of
2.1.2. Visual Stimulator
