Some Women Without the Brain’s Olfactory Bulbs Can Still Smell. Scientists Say It Makes No Sense

Left-handed women missing the brain structures were still able to smell as well–or better—than average

Bulbless Brain
A brain with a normal olfactory bulb on the left and a brain lacking the bulb on the right. Weizmann Institute of Science

The way we perceive the world around us is super complex, but researchers seem to have a grasp of the basics—rod and cones in our eyes are used to see, tastebuds on our tongue help us taste, a maze of parts in our ears let us hear, nerve endings in our skin make us feel and the olfactory bulb toward the back of the nose allows us to smell.

But a new paper published in the journal Neuron has scientists questioning what the nose knows. Researchers have identified two women without olfactory bulbs that were still able to smell just as well, or better, than the average person.

The finding happened by chance. Researchers at the Weizmann Institute of Science in Israel were conducting MRI scans of people with a good sense of smell. So the study team was shocked when they looked at the brain scan of one participant and found the 29-year-old, left-handed woman did not appear to have an olfactory bulb.

The study’s senior author Noam Sobel, a neurobiologist at the Weizmann Institute of Science, tells Yasemin Saplakoglu at Live Science that at first, they thought there was a mistake and perhaps the woman did not notice the part of the ad asking for volunteers with a good sense of smell. But the woman insisted that she could smell just fine, and in fact, had a sense of smell superior to most people.

“We tested her smelling faculties in every way would could think of, and she was right,” Sobel says in a statement. “Her sense of smell was indeed above average. And she really doesn’t have olfactory bulbs. We conducted another scan with especially high-resolution imaging, and saw no signs of this structure.”

This first woman without an olfactory bulb that they tested also happened to be left-handed. Both left-handedness and lacking an olfactory bulb are traits known to affect how the brain is organized. The team decided to investigate further, so they sought out a control group of left-handed women to compare the original subject to. Eight women came in, no luck.

But then “[w]hen the ninth subject in the ‘control’ group also turned out to be lacking olfactory bulbs, alarm bells started ringing,” says the study’s lead author Tali Weiss in a statement.

Finding two women without olfactory bulbs, but with a sense of smell seemed like too much of a coincidence, so the team did a deep dive into the data, analyzing MRI brain scans from the Human Connectome Project, which has published over 1,113 brain scans. From that data set, which includes 606 women, they found three more female subjects who did not have olfactory bulbs, but retained their sense of smell. One of those women was also left-handed. According to the data, the team estimates that about 0.6 percent of women globally and 4.25 percent of left-handed women lack an olfactory bulb but still retain a sense of smell. None of the men in the database appeared to have the same ability.

The team also tested the sense of smell of the two women without bulbs and 140 others. The pair both showed an ability to smell on par with the women with olfactory bulbs, and their “olfactory perceptual fingerprint,” or the unique way they perceive smells, were more closely matched to each other than the other participants in the study. There were some anomalies. For instance, neither woman could identify rose-like odors.

How exactly the women are able to smell without their sense organ is not known. “I’m not sure that our textbook view of how the [olfactory] system works is right,” Sobel tells Sofie Bates at Science News.

The team does have a theory about how the smelling works. It’s thought that scents are mapped onto the olfactory bulb, with certain areas corresponding to certain smells. But it’s possible that in these cases, scents are mapped on a different area of the brain.

“Current ideas posit the olfactory bulb as a ‘processing center’ for information that is complex and multi-dimensional, but it may be that our sense of smell works on a simpler principle, with fewer dimensions,” Sobel says in a statement. “It will take high resolution imaging – higher than that approved for use on humans today – to resolve that issue. But the fact remains that these women smell the world in the same way as the rest of us, and we don't know how they achieve this.”

Not everyone agrees that these subjects are totally abnormal. “I am not convinced that the women are indeed missing their bulbs,” Jay Gottfried of the University of Pennsylvania, who was not involved in the study, tells Bates.

It’s possible that small bits of olfactory tissue or microscopic structures remain that are too small for the MRI to pick up. Other researchers tells Saplakoglu that it’s possible the elements of olfactory perception are displaced, differently shaped or disorganized, and therefore, unidentifiable on the scans.

In the meantime, if the brain is able to compensate for the lack of an olfactory bulb, the team suggests doctors should start screening children for anosmia, or the lack of the ability to smell.

They write in the paper:

Currently in the West, newborns are tested for vision, audition, and more, all within the first hours or days after birth. It is perhaps time to start screening children, or perhaps even babies, using non-verbal measures of olfaction. Early identification of reduced olfaction could then perhaps be addressed within an odor enrichment program in the aim of triggering compensatory mechanisms, [which would promote the formation of olfaction areas in other parts of the brain.]

The team is currently searching out more people lacking olfactory bulbs for follow-up studies. If there really is an alternate pathway to identify smell, the hope is that it could lead to treatments for people who can’t smell.

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