Cognitive Neuroscience Lab    

Olfactometer Construction


This page describes the construction, caveats, and cleaning of a simple olfactometer that can be used for odor delivery in electrophysiological, fMRI, and psychophysical studies of human and animal odor response.

The first thing that should be noted is that there are other olfactometers available that have far better control of the stimulus. This olfactometer provides a rise time that depends upon flow rate from about 45msec (with 3L/min) to about 100msec (with 1.5L/min). Odor turn off, lasts roughly about 1.5 times as long as the rise time. This can hardly be called a square wave but it is a salient odor change and, given the variability of inhalation, may be completely suitable for many applications such as fMRI and some forms of electrophysiology.

The design described here is a modification of a design by Lorig,T.S., Elmes, D.G., Zald, D.H. & Pardo, J.V. (1999). A computer-controlled olfactometer for fMRI and electrophysiological studies of olfaction. Behavior Research Methods, Instruments & Computers, 31,370-375.

The new design is more efficient to build and somewhat less expensive.











Olfactometer Chassis




The design operates very simply. In essence, air is switched by a computer controller through different air lines and over different odorants placed on syringe filters. To avoid any increases in air flow, one unodorized line is stopped during odor stimulation making the net change in air zero.

The air source for the olfactometer is a commercially available air pump made to supply nebulizers (Respironics). If desired, this air flow is filtered through a charcoal filter to remove any room air odors (If you use a charcoal filter, you MUST filter the air for particulates lest you administer charcoal dust to your subjects!). After passing through the particulate filters the flow is divided and metered through flowmeters (rotometers). One of these valves provides a constant low volume air stream that is unswitched and always on. The other flowmeter provides the air that will be passed over the odors. This stream is also divided and passed to two solenoid valves. Valve A is a single valve that is open when not activiated (Normally On - NO). The other valve is a gang type valve that can have from 1 to 6 solenoids (B1-6). To send a odor to a subject, the computer turns on Valve A (stopping air flow in that line) and turns on Valve Bn opening air flow in that line. The syringe filter that is connected to line Bn contains odor and the air now passes over the filter and through the manifold to the subject. Turning the valves off stops air flow over the filter paper and stops the blockage cause by actuating Valve A.

Because the switching in the valves leads to very brief air flow changes (around 20msec) the constant flow line acts as a "buffer" for the air flow change.





Valve Assembly


The photo on the right shows the inside of the chasis. At the far right is the air pump (placed on foam to reduce noise) and at the left is the relay controller (marked "Measurement Advantage") and a 4 channel valve assembly (each metal cylinder is a solenoid valve). Note the use of spiral wrap to wrangle the tubing.



Inside view

Manifold Assembly


The manifold is one of the few pieces of the olfactometer that requires fabrication. The teflon disk must be drilled and tapped to accommodate the compression fittings and syringe filters. The photo at the right shows this assembly ready for use. Note that glass or teflon balls (4mm dia) are placed in each of the syringe filters and also at the top of the luer fitting. These act as a pair of ball valves and prevent the odorized air from diffusing to the subject and diffusing back down the tubing. The tapped line in the middle of the disk (lower side) is for the constant air flow line. Note that, due to the ball valves, this must remain in a horizontal position. Otherwise, odor will leak into the tubing and subject. Also note that you will need to plug the horizontal drilled holes with nylon screws to prevent air leakage.

If you are using the olfactometer for an application other than fMRI, you may find increased durability by using stainless steel balls and luer fittings.

The photo on the far right shows the manifold connected to a microphone holder that can be used to swing the manifold into and out of place as the subject alternatively is tested and takes breaks.

The Y adapter is used for birhinic stimulation but many other approaches may also be used. In our applications, it is very important to monitor nasal breathing so a dual lumen nasal cannula (Nellcor Puritan Bennett) is used. Teflon tubing is inserted into one side of the cannula and the other opening is connected to a pressure transducer (Biologic Sleepscan) to evaluate nasal breathing.



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