Sniff and sniff
Why do we sniff our noses frantically when someone asks us if we smell "that" too? - Because our brain is told by the increased air flow that it has to carry out an odor analysis. According to modern imaging methods, "sniffing" and "smelling" are different processes for the brain. "We seem to have discovered that the processing of olfactory signals occurs separately in two distinct processes," says John Gabrieli, assistant professor of psychology at Stanford University Medical Center. He distinguishes the increased breathing through the nose - the "sniffing" - from the actual "smelling", in which scents meet nerve cells (Nature from 19. March 1998).
Gabrieli and his colleagues studied the brain activity of subjects who were awake and responding to instructions. With the help of magnetic resonance imaging, they recorded the increased oxygen turnover in the individual areas. After subtracting all activity patterns caused by other activities, the specific signals for sniffing and smelling were left.
When the subjects sniffed the air without any odorant present, the area of the piriform cortex showed the greatest activity. However, if there was really something to smell, more oxygen was converted in the frontal lobe. The active centers overlap in several places. Gabrieli sees the reason in the fact that the sniffing process triggers smelling. "Of course, our nose is open all the time. But we can still compare it to opening our eyes. It can be understood as a warning that an odor is about to follow - a kind of mechanism to attract attention."
"Some people laughed at me when I explained this to them, but I'll use the example of a public toilet to demonstrate," says Gabrieli. "It's only with the first sniff that the smell really knocks you out. If you don't inhale intensively, you don't really notice the smell."
According to the researchers, it is not the movement of the nasal muscles that is decisive, but the airflow through the nose. Attempted sniffing with pinched nostrils does not alarm the brain, but a stream of air blown into it does. A good wind should do the same.
Gabrieli addresses another serious application of his research: Many people lose their ability to smell. Sometimes these are early signs of Parkinson's or Alzheimer's disease. With the distinction between sniffing and actual smelling, the causes of the sensory loss can now be better narrowed down.
The Heidelberger Verlag Spektrum der Wissenschaft is the operator of this portal. Its online and print magazines, including "Spektrum der Wissenschaft", "Gehirn&Geist" and "Spektrum – Die Woche", report on current research findings.
