Human odor exploration behavior is influenced by olfactory function and interest in the sense of smell

Cattle olfaction-Dairy cows' interest in odors and factors affecting their odor exploration behavior

Animals use their sense of smell in various situations, including foraging, selecting mates, and assessing predation risks. Consequently, odors are likely to affect numerous handling and management practices involving farm animals. Cattle have a well-developed sense of olfaction that may play a larger role in their everyday life than is currently considered. The current body of research on cattle olfactory abilities is, however, surprisingly scarce. The aim of this study was to investigate if cows can detect and discriminate 4 odors of natural, nonsocial origin, and if any of the specific odors evoke more interest (measured as sniffing time) than others. We further aimed to assess if age, parity, and breed affected this. In addition, we investigated olfactory-exploration behavior (other than sniffing: licking, biting, flehmen, head movements, backing, snorting) of dairy cattle and ear positions to elucidate if certain behaviors and ear positions are restricted to certain odors. Twenty-eight cows (16 Swedish Holstein, 12 Swedish Red) were enrolled in a habituation-dishabituation test where they were tested in pairs on 4 natural odors (essential oils, nondiluted): cedarwood, lavender, orange, and peppermint. The test was conducted on individual animals in their home environment where each odor was presented 3 times in a row for 1 min each with an intertrial interval of 2 min. Following another 2-min interval without the first odor, the cow was presented with a different odor, with order of odor presentation balanced among animals. Duration of sniffing (muzzle in proximity to) the odor box, occurrence of licking or biting the odor box, and avoidance behavior (backing and head movements), and ear positions were recorded. Although the results showed a decrease in sniffing time over repeated presentations of the same odor, only the first-to-third presentation of cedarwood and first-to-second and first-to-third presentation of orange differed significantly. Only some dishabituation trials elicited a significant reinstatement of sniffing; hence, it is unclear if cows were able to discriminate all odors from each other. Testing cows in pairs potentially led to brief pre-exposure to odors, thereby affecting overall sniffing durations. More studies are thus needed to elucidate if cows can recognize but also discriminate the odors. Cows did not show a clear interest in any particular odor, though they numerically sniffed cedarwood the most and orange the least. Younger cows expressed more sniffing behavior than older cows regardless of odor, and younger cows also expressed axial ear positions for longer. Specific odors did not elicit more of any of the ear positions than others. Behaviors indicative of avoidance reactions (head movements, backing, snorting) were generally low for all odors, but Swedish Holstein cows expressed more backward ear positions than Swedish Red, highlighting the need for further studies including various cattle breeds. We encourage future studies on olfactory abilities and preferences, as well as refinement of methods to further adapt testing regimens for cattle olfaction.

Horse odor exploration behavior is influenced by pregnancy and age

In spite of a highly developed olfactory apparatus of horses, implying a high adaptive value, research on equine olfaction is sparse. Our limited knowledge on equine olfaction poses a risk that horse behavior does not match human expectations, as horses might react fearful when exposed to certain odors, which humans do not consider as frightening. The benefit of acquiring more knowledge of equine olfaction is therefore twofold; (1) it can aid the understanding of horse behavior and hence reduce the risk of dangerous situations, and (2) there may be unexplored potential of using odors in several practical situations where humans interact with horses. This study investigated behavior and olfactory sensitivity of 35 Icelandic horses who were presented with four odors: peppermint, orange, lavender and cedar wood in a Habituation/Dishabituation paradigm. The response variables were sniffing duration per presentation and behavioral reaction (licking, biting, snorting, and backing), and data were analyzed for potential effects of age, sex and pregnancy. Results showed that habituation occurred between successive odor presentations (1st vs. 2nd and 2nd vs. 3rd presentations: P < 0.001), and dishabituation occurred when a new odor was presented (1st vs. 3rd presentations: P < 0.001). Horses were thus able to detect and distinguish between all four odors, but expressed significantly longer sniffing duration when exposed to peppermint (peppermint vs. orange, lavender and cedar wood: P < 0.001). More horses expressed licking when presented to peppermint compared to cedar wood and lavender (P = 0.0068). Pregnant mares sniffed odors less than non-pregnant mares (P = 0.030), young horses (age 0-5 years) sniffed cedar wood for longer than old horses (P = 0.030), whereas sex had no effect (P > 0.050). The results show that horses’ odor exploration behavior and interest in odors varies with age and pregnancy and that horses naïve to the taste of a substrate, may be able to link smell with taste, which has not been described before. These results can aid our understanding of horses’ behavioral reactions to odors, and in the future, it may be possible to relate these to the physiology and health of horses.

Motor Cortex Response to Pleasant Odor Perception and Imagery: The Differential Role of Personality Dimensions and Imagery Ability

Background

Neuroimaging studies have shown a complex pattern of brain activation during perception of a pleasant odor and during its olfactory imagery. To date, little is known regarding changes in motor cortex excitability during these tasks. Bergamot essential oil (BEO) is extensively used in perfumes and cosmetics for its pleasantness. Therefore, to further our understanding of the human sense of smell, this study aimed to investigate the effect of perception and imagery of a pleasant odor (BEO) on motor cortex using Transcranial magnetic stimulation (TMS).

Materials and Methods

We examined the primary motor cortex (M1) excitability during perception of a pleasant odor (BEO) or perception of odorless saline (experiment 1). Furthermore, we tested the effect of olfactory imagery (OI) of BEO on corticospinal excitability (experiment 2). The increase in motor evoked potential (MEP) amplitude was correlated with personality dimensions scores, pleasantness, vividness, and general imagery ability.

Results

The results indicate that the corticospinal excitability changed after both perception and imagery of a pleasant odor (BEO). The correlation analysis shows an association with neuroticism personality trait (experiment 1) and with general olfactory imagery ability (experiment 2).

Conclusion

Both perception of a pleasant odor and its olfactory imagery modulate motor cortex excitability. The enhanced brain activation is affected by specific individual characteristics. Overall, our findings provide physiological evidence for a complex interaction between the olfactory and motor systems.