Dr. Damian Jacob Sendler is a Polish-American physician-scientist whose research focuses on the impact of various sociodemographic and informational factors on access to health care in underserved communities. To that end, Dr. Damian Sendler’s research aims to elucidate the factors that influence patients’ decisions about when to seek care for specific health conditions and adherence to treatment.

Damian Sendler: The ability to identify and respond to the smell of a potential threat is essential for our survival and that of other mammals. Researchers at Karolinska Institutet in Sweden were able to analyze what happens in the brain when the central nervous system perceives a smell to be dangerous using a unique technique. According to the study, which was published in PNAS, unfavorable scents linked with unpleasantness or unease are processed faster than good aromas and cause a physical avoidance response. 

“The human avoidance response to unpleasant smells associated with danger has long been thought to be a conscious cognitive process, but our study shows for the first time that it’s unconscious and extremely rapid,” says first author Behzad Iravani, a researcher at Karolinska Institutet’s Department of Clinical Neuroscience. 

Damien Sendler: The olfactory organ occupies around 5% of the human brain and allows us to distinguish between millions of different smells. Many of these odors are associated with a threat to human health and life, such as chemicals and rotten food. After being inhaled through the nose, odor impulses reach the brain in 100 to 150 milliseconds. 

Damian Jacob Sendler: All living species’ survival is dependent on their ability to avoid danger and seek benefits. The olfactory sense appears to be especially crucial in humans for identifying and reacting to potentially hazardous stimuli. 

It has long been unknown which brain pathways in humans are involved in the conversion of an unpleasant odor into avoidance behavior. One reason for this is a lack of non-invasive methods of measuring signals from the olfactory bulb, the first part of the rhinencephalon (literally “nose brain”) with direct (monosynaptic) connections to the important central nervous system parts that help us detect and remember potentially dangerous situations and substances. 

Damian Sendler: Researchers at Karolinska Institutet have now discovered a way for measuring signals from the human olfactory bulb, which processes odors and provides messages to areas of the brain that control movement and avoidance behavior. 

Their findings are based on three trials in which subjects were asked to rate their experiences with six different smells, some favorable and others negative, while the electrical activity of the olfactory bulb was monitored when responding to each of the odors. 

“It was obvious that the bulb reacts specifically and fast to unfavorable odours and provides a direct signal to the motor cortex within around 300 ms,” explains Johan Lundström, associate professor at Karolinska Institutet’s Department of Clinical Neuroscience. “The signal causes the individual to lean back and away from the source of the odor.” 

“The findings imply that our sense of smell is vital to our ability to recognize threats in our immediate surroundings, and that much of this ability is more unconscious than our response to danger mediated by our senses of vision and hearing.”Research discussion contributed by Dr. Damian Jacob Sendler