A new study published in the Journal of Neuroscience indicates that the sense of smell is significantly influenced by cues from other senses, whereas the senses of sight and hearing are much less affected.
A popular theory of the brain holds that its main function is to predict what will happen next, so it reacts mostly to unexpected events. Most research on this topic, called predictive coding, has only focused on what we see, but no one knows if the different senses, such as smell, work in the same way.
To figure out more about how smell relates to how we handle different sensory impressions, the researchers conducted a study with three experiments, two behavioral experiments, and one experiment using the brain imaging method fMRI at Stockholm University Brain Imaging Centre (SUBIC).
"The main finding is that smelling was much more dependent on predictions than vision was. This is interesting because many people think that smell is primitive and reactive, when our research shows it is in fact quite sophisticated and proactive," says Stephen Pierzchajlo, PhD Student at the Department of Psychology, and main author of the study.
The study shows how important it is for our different senses to be able to use correct cues when we classify different sensory impressions.
Sensory Interactions and Predictions
"We have all experienced that we react to when an unexpected smell appears, for example when we enter someone's flat and encounter a new smell. Our research shows that the sense of smell is highly influenced by the cues from other senses, while the sense of sight and hearing are affected to a much lesser extent," says Jonas Olofsson, professor at the Department of Psychology, and co-author of the study.
The researchers also show that when the brain tries to identify odors that it had not expected, both the olfactory and visual brains are activated, despite the absence of visual cues in the task.
"The olfactory brain thus has a completely unique way of processing smells and it is about whether the smells are expected or not. The sense of smell warns us of smells that we had not expected, and engages the visual brain, perhaps to be able to see what it is that smells. It's a smart function because we humans are so bad at recognizing smells if we don't get clues," says Jonas Olofsson.
In the experiments, participants listened to spoken word cues, such as "lemon", and then received a picture or smell, and participants quickly decided whether it matched with the cue, for example with a lemon picture or smell, or did not match, for example with a rose picture or smell.
"We noticed that overall, the expected pictures and smells led to quicker decisions, which fits well with predictive coding theory. We used the difference in response speed to compare the senses with each other – a bigger delay for unexpected stimuli means that the sense relies more on predictions," says Stephen Pierzchajlo.
The study is the first concluded part of his PhD research.
"The human sense of smell is not a reactive, but a proactive sense. It uses a unique brain strategy to process unexpected smells in order to understand what the smells are," says Stephen Pierzchajlo.
Reference: "Olfactory categorization is shaped by a transmodal cortical network for evaluating perceptual predictions" by Stephen Pierzchajlo, Teodor Jernsäther, Lara Fontana, Rita Almeida and Jonas K. Olofsson, 31 March 2024, Journal of Neuroscience.
DOI: 10.1523/JNEUROSCI.1232-23.2024
The study was funded by the Knut och Alice Wallenbergs Stiftelse, Swedish Research Council, Stockholm University.
News
Fever-Proof Bird Flu Variant Could Fuel the Next Pandemic
Bird flu viruses present a significant risk to humans because they can continue replicating at temperatures higher than a typical fever. Fever is one of the body’s main tools for slowing or stopping viral [...]
What could the future of nanoscience look like?
Society has a lot to thank for nanoscience. From improved health monitoring to reducing the size of electronics, scientists’ ability to delve deeper and better understand chemistry at the nanoscale has opened up numerous [...]
Scientists Melt Cancer’s Hidden “Power Hubs” and Stop Tumor Growth
Researchers discovered that in a rare kidney cancer, RNA builds droplet-like hubs that act as growth control centers inside tumor cells. By engineering a molecular switch to dissolve these hubs, they were able to halt cancer [...]
Platelet-inspired nanoparticles could improve treatment of inflammatory diseases
Scientists have developed platelet-inspired nanoparticles that deliver anti-inflammatory drugs directly to brain-computer interface implants, doubling their effectiveness. Scientists have found a way to improve the performance of brain-computer interface (BCI) electrodes by delivering anti-inflammatory drugs directly [...]
After 150 years, a new chapter in cancer therapy is finally beginning
For decades, researchers have been looking for ways to destroy cancer cells in a targeted manner without further weakening the body. But for many patients whose immune system is severely impaired by chemotherapy or radiation, [...]
Older chemical libraries show promise for fighting resistant strains of COVID-19 virus
SARS‑CoV‑2, the virus that causes COVID-19, continues to mutate, with some newer strains becoming less responsive to current antiviral treatments like Paxlovid. Now, University of California San Diego scientists and an international team of [...]
Lower doses of immunotherapy for skin cancer give better results, study suggests
According to a new study, lower doses of approved immunotherapy for malignant melanoma can give better results against tumors, while reducing side effects. This is reported by researchers at Karolinska Institutet in the Journal of the National [...]
Researchers highlight five pathways through which microplastics can harm the brain
Microplastics could be fueling neurodegenerative diseases like Alzheimer's and Parkinson's, with a new study highlighting five ways microplastics can trigger inflammation and damage in the brain. More than 57 million people live with dementia, [...]
Tiny Metal Nanodots Obliterate Cancer Cells While Largely Sparing Healthy Tissue
Scientists have developed tiny metal-oxide particles that push cancer cells past their stress limits while sparing healthy tissue. An international team led by RMIT University has developed tiny particles called nanodots, crafted from a metallic compound, [...]
Gold Nanoclusters Could Supercharge Quantum Computers
Researchers found that gold “super atoms” can behave like the atoms in top-tier quantum systems—only far easier to scale. These tiny clusters can be customized at the molecular level, offering a powerful, tunable foundation [...]
A single shot of HPV vaccine may be enough to fight cervical cancer, study finds
WASHINGTON -- A single HPV vaccination appears just as effective as two doses at preventing the viral infection that causes cervical cancer, researchers reported Wednesday. HPV, or human papillomavirus, is very common and spread [...]
New technique overcomes technological barrier in 3D brain imaging
Scientists at the Swiss Light Source SLS have succeeded in mapping a piece of brain tissue in 3D at unprecedented resolution using X-rays, non-destructively. The breakthrough overcomes a long-standing technological barrier that had limited [...]
Scientists Uncover Hidden Blood Pattern in Long COVID
Researchers found persistent microclot and NET structures in Long COVID blood that may explain long-lasting symptoms. Researchers examining Long COVID have identified a structural connection between circulating microclots and neutrophil extracellular traps (NETs). The [...]
This Cellular Trick Helps Cancer Spread, but Could Also Stop It
Groups of normal cbiells can sense far into their surroundings, helping explain cancer cell migration. Understanding this ability could lead to new ways to limit tumor spread. The tale of the princess and the [...]
New mRNA therapy targets drug-resistant pneumonia
Bacteria that multiply on surfaces are a major headache in health care when they gain a foothold on, for example, implants or in catheters. Researchers at Chalmers University of Technology in Sweden have found [...]
Current Heart Health Guidelines Are Failing To Catch a Deadly Genetic Killer
New research reveals that standard screening misses most people with a common inherited cholesterol disorder. A Mayo Clinic study reports that current genetic screening guidelines overlook most people who have familial hypercholesterolemia, an inherited disorder that [...]
