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Neuron. 2020 Jan 8;105(1):35-45.e5. doi: 10.1016/j.neuron.2019.10.006. Epub 2019 Nov 6.

Human Olfaction without Apparent Olfactory Bulbs.

Author information

1
The Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science, Rehovot, Israel; Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel. Electronic address: tali.weiss@weizmann.ac.il.
2
The Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science, Rehovot, Israel; Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel.
3
The Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science, Rehovot, Israel.
4
The Florey Institute of Neuroscience and Mental Health, Melbourne, VIC, Australia; The Florey Department of Neuroscience and Mental Health, University of Melbourne, Melbourne, VIC, Australia.
5
The Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science, Rehovot, Israel; Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel. Electronic address: noam.sobel@weizmann.ac.il.

Abstract

The olfactory bulbs (OBs) are the first site of odor representation in the mammalian brain, and their unique ultrastructure is considered a necessary substrate for spatiotemporal coding of smell. Given this, we were struck by the serendipitous observation at MRI of two otherwise healthy young left-handed women, yet with no apparent OBs. Standardized tests revealed normal odor awareness, detection, discrimination, identification, and representation. Functional MRI of these women's brains revealed that odorant-induced activity in piriform cortex, the primary OB target, was similar in its extent to that of intact controls. Finally, review of a public brain-MRI database with 1,113 participants (606 women) also tested for olfactory performance, uncovered olfaction without anatomically defined OBs in ∼0.6% of women and ∼4.25% of left-handed women. Thus, humans can perform the basic facets of olfaction without canonical OBs, implying extreme plasticity in the functional neuroanatomy of this sensory system.

KEYWORDS:

anosmia; brain plasticity; functional brain imaging; left-handedness; odor coding; olfaction; olfactory bulb; olfactory perception; structural brain imaging

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