Human olfactory lateralization requires trigeminal activation.
Rats are able to lateralize odors. This ability involves specialized neurons in the orbitofrontal cortex which are able to process the left, right and bilateral presentation of stimuli. However, it is not clear whether this function is preserved in humans. Humans are in general not able to differentiate whether a selective olfactory stimulant has been applied to the left or right nostril; however exceptions have been reported. Following a screening of 152 individuals with an olfactory lateralization test, we identified 19 who could lateralize odors above chance level. 15 of these "lateralizers" underwent olfactory fMRI scanning in a block design and were compared to 15 controls matched for age and sex distribution. As a result, both groups showed comparable activation of olfactory eloquent brain areas. However, subjects with lateralization ability had a significantly enhanced activation of cerebral trigeminal processing areas (somatosensory cortex, intraparietal sulcus). In contrast to controls, lateralizers furthermore exhibited no suppression in the area of the trigeminal principal sensory nucleus. An exploratory study with an olfactory change detection paradigm furthermore showed that lateralizers oriented faster towards changes in the olfactory environment. Taken together, our study suggests that the trigeminal system is activated to a higher degree by the odorous stimuli in the group of "lateralizers". We conclude that humans are not able to lateralize odors based on the olfactory input alone, but vary in the degree to which the trigeminal system is recruited.
University of Dresden Medical School, Smell & Taste Clinic, Dept. of Otorhinolaryngology, Fetscherstr. 74, 01307 Dresden, Germany; University of Gothenburg, Institute of Neuroscience and Physiology, Sahlgrenska University Hospital, Blå Stråket 5, 413 45 Gothenburg, Sweden. Electronic address: ilona.croy@neuro.gu.se.
Ilona
I
Croy
University of Dresden Medical School, Smell & Taste Clinic, Dept. of Otorhinolaryngology, Fetscherstr. 74, 01307 Dresden, Germany.
Max
M
Schulz
University of Dresden Medical School, Smell & Taste Clinic, Dept. of Otorhinolaryngology, Fetscherstr. 74, 01307 Dresden, Germany.
Anna
A
Blumrich
University of Dresden Medical School, Smell & Taste Clinic, Dept. of Otorhinolaryngology, Fetscherstr. 74, 01307 Dresden, Germany.
Cornelia
C
Hummel
University of Dresden Medical School, Department of Neuroradiology, Fetscherstr. 74, 01307 Dresden, Germany.
Johannes
J
Gerber
University of Dresden Medical School, Smell & Taste Clinic, Dept. of Otorhinolaryngology, Fetscherstr. 74, 01307 Dresden, Germany.
Thomas
T
Hummel
D000293:Adolescent; D000328:Adult; D001288:Attention / Q000502:physiology; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009812:Odorants; D055696:Olfactory Perception / Q000502:physiology*; D010296:Parietal Lobe / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology*; D014278:Trigeminal Nuclei / Q000502:physiology*; D055815:Young Adult
Attention; Lateralization; Localization; Myelinated; Olfaction; fMRI