Using Your Nose

by Ben Wilbert
December 2004

While most scientists who study human brain evolution tend to regard something people do very well, such as language, Dr. Tyler Lorig, PhD at Washington & Lee University studies one of the least understood senses, and something people tend to do poorly: smell. He studies the olfactory (a.k.a. sense of smell) system in his lab, specifically how the brain responds to an odor. His work led him to
develop his own olfactometer, an instrument used to deliver and help measure odors. He built it out of mostly off-the-shelf chromatography parts that required little modification. All parts of the olfactometer that could contaminate smells are high purity, and hence minimize residual odors that could affect the experiment results.

Overall, the instrument needed essentially seven features:
(1) computer control;
(2) effective delivery of a variety of odors, in series or randomly;
(3) production of an odor stimulus of selectable and reliable duration in a constant airstream, without any additional type of ancillary stimulation (e.g., tactile, auditory);
(4) resistance to contamination;
(5) durability;
(6) ease of operation, refilling, and cleaning; and
(7) low cost (Lorig et al. 1999). And since he uses the olfactometer near an fMRI (functional magnetic resonance imaging), to measure brain activity, it obviously has to be free of ferrous metals, which will wreak havoc near the magnet.

Following the drawing above, air from a compressor is passed through a charcoal filter to remove odors and then through particulate filters to prevent charcoal dust from being administered to the test subject. After passing through the particulate filters the flow is divided and metered through variable-area flowmeters. One of the lines is always open and provides a constant low-volume air stream. 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 normally open. The other valve is a multi-port valve that can have from 1 to 6 individual normally closed solenoid valves (B1-6). To send an odor to a subject, the computer turns on valve A (stopping airflow in that line) and turns on valve Bn commencing airflow in that line. The syringe filter connected to line Bn contains odor, and the air now passes over the filter and through the manifold to the subject. Turning the valve off stops airflow over the filter paper and stops the blockage cause by actuating valve A. To avoid any increases in airflow, one non-odorized line is stopped during odor stimulation making the net change in air zero.

Because the switching in the valves lead to very brief airflow changes (around 20 milliseconds) the constant flow line acts as a buffer for the airflow change, thereby reducing any extraneous sensory stimulation to the test subject.

In relatively normal test subjects, Lorig finds people have measurable brain activity induced by odors, even when the test subject reports not smelling anything!

“Some of the research done shows we are exquisitely sensitive to smells, contrary to our expectation.” states Lorig.

Furthermore, when an odorous chemical is blindly switched from one to another—neither reported as smelled—the brain responds differently. There’s now understanding of the connection between olfaction and certain health problems, and Lorig states he would like to see olfaction analysis become
simplified and used more in clinical applications. Current research examines the relationship between olfaction and maladies such as Parkinson’s Disease, Huntington’s Disease, Korsakoff’s Syndrome, Schizophrenia, Depression, and Alzheimer’s Disease (AD). Recent evidence suggests that areas in the central nervous system processing olfactory information are affected at the early stages of AD, even before the onset of cognitive decline, and that olfactory dysfunction might be an early indicator of AD (Murphy, 1999). Aside from aiding pathological diagnosis, Lorig’s current and future toils include research on how the brain is organized, pathways the brain uses to process odors, and the many relationships between smelling and the other senses.