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By Root 875 0

There were Decisives—people who sniffed and promptly announced their rating—and there were the Agonizers, who sniffed and resniffed and sniffed again before summoning up a rating. Every combination of behavior and decision-making style turned up in my lab: Delicate sniffers who were very decisive, Honkers who were Agonizers, and so on. These patterns were so consistent that after two or three squeeze bottles I could predict how long the entire test would take. A diverse range of local oddballs answered our recruiting ads. Once, in the middle of a test, my research assistant handed a sample of patchouli around the screen. There was some squeezing and sniffing, followed by a long silence. Finally she looked around to find that her subject had poured the sample into his hand and was massaging it into his beard. He said he liked how it smelled.

Intuitively, it seems the more one sniffs, the better one smells. Like dogs at a fire hydrant, multisniffers must be extracting every last bit of information from a smell. But are they? David Laing systematically controlled sniffing to see how it affected a person’s ability to detect and describe a smell. Sometimes he allowed his subjects to sniff with their natural pattern; other times he told them exactly how many sniffs to take, how long to wait between sniffs, or how big a sniff to take. When subjects were limited to a single sniff, they took one that resembled the first in a natural sniffing episode. Whether the sniff was the first-and-only or the first-of-many, it did not appear to vary with odor strength. After many experiments he could state his findings in a nutshell: “a single natural sniff provides as much information about the presence and intensity of an odour as do seven or more sniffs.” A natural first sniff can’t be beat. (For the technically minded, the optimum sniff has an inhalation rate of 30 liters per minute, a volume of 200 cubic centimeters, and a minimum duration of .40 to .45 seconds.)

There are two aspects to sniffing that are reflected in how we use the verb “sniff.” It can refer to a purely mechanical act (the drawing of air “through the nose with short or sharp audible inhalations”) or to an olfactory experience (“to smell with a sniff or sniffs”). The dictionary’s dichotomy between physical and sensory sniffing is programmed into the central nervous system at a profound level. The brain is not a passive recipient of smells drawn up the nose; it actively manages the acquisition of odor by the nose, and it does so on a time scale of milliseconds.

UC Berkeley smell researcher Noam Sobel was puzzled to find smell-related activity in the cerebellum, a brain area principally involved in tactile discrimination and the control of motor movements. When he and his lab team followed up, they discovered that two parts of the cerebellum were involved in sniffing. One was a smell-activated area; it lit up when a person smelled an odor. The stronger the odor, the greater the activation. Normally this area is activated in the course of sniffing scented air. Sobel found it was also activated by passive smelling, where odors were puffed into the subject’s nose through a tube while they held their breath. The second area of the cerebellum is sniff-activated; it lights up during the physical act of sniffing, but not during passive smelling. The sensation of air flowing through the nose explains the activation in the tactile part of the brain. When topical anesthetic was applied to a subject’s nasal passages to numb the nose, brain activity plunged. Together, two brain areas adjust sniff size to odor strength. This feedback happens very quickly: less than two-tenths of a second into the sniff. (By measuring with far greater precision than was available to Donald Laing, Sobel’s group found that the first sniff of a series was not fixed—only its first 160 milliseconds were.) As a strong odor is detected, the cerebellum signals the respiratory muscles to throttle back on the sniff. What appeared at first to be anomalous brain activity led Sobel and his team to a new understanding