Jean-Louis Millot

Sex differences in human olfaction: between evidence and enigma.

The sex of individuals plays an important part in determining their olfactory abilities, with females generally being superior to males. The present review examines the way in which sex differences influence sensitivity, identification, familiarity, and recognition of odours. It also examines whether sex differences are more pronounced with some odours than others, and how sex differences are affected by the manner of testing. Two different explanations for the superiority of females over males in olfaction are evaluated.

Effects of ambient odors on reaction time in humans

The perception of odors is well identified as having strong emotional correlates. The effects of ambient odors on arousal level and task performance have also been suspected but remain poorly assessed in the literature. The present study compared the reaction times of subjects between ambient odor conditions (pleasant and unpleasant) and a no-odor condition. The results showed that the reaction time in simple tasks (responses to visual or auditory stimulation) significantly decreased in the ambient odor conditions (whatever the pleasantness of the odors) compared with the no-odor condition. These results underline the importance of the olfactory environment in human behavior.

Effects of pleasant and unpleasant ambient odors on human voice pitch

The perception of odors is well identified as having strong emotional correlates. It is also well known that the acoustic characteristics of the voice differ according to the emotional state. This study compared some acoustic features of the voice of 18 subjects reading the same text in pleasant (lavender) and unpleasant (pyridine) ambient odor conditions. The results revealed that the pitch of the voice was higher in the pleasant than in the unpleasant condition. These findings are consistent with the hypothesis of local and functional convergences of encoding vocal emotion and hedonic perception of odors.

Complexity of olfactory lateralization processes revealed by functional imaging: a review.

Currently available techniques used in neurosciences and particularly cerebral imaging are contributing to a better understanding of human perception and the treatment of sensorial information. In this field, the chemical senses (taste and smell) have received little attention when compared with the auditory, visual and tactile senses. Nevertheless, recent research has been trying to overcome this. Brain regions involved in the processing of olfactory information have been investigated in several studies including a large number dealing with the question of lateralization. However, functional asymmetry in olfaction has still not been resolved and the resulting data have not been homogeneous. In this field, the contribution of cerebral imaging studies is very important insofar as it shows that the processes of functional lateralization in olfaction depend on many factors (nature of stimulus, nature of task, characteristics of subjects ...) that future research will have to consider.

Patterns of cerebral activation during olfactory and trigeminal stimulations.

It is well known that most odorants stimulate both the olfactory system and the trigeminal system. However, the overlap between the brain processes involved in each of these sensorial perceptions is still poorly documented. This study aims to compare fMRI brain activations while smelling two odorants of a similar perceived intensity and pleasantness: phenyl ethyl alcohol (a pure olfactory stimulus) and iso‐amyl‐acetate (a bimodal olfactory‐trigeminal stimulus) in a homogeneous sample of 15 healthy, right‐handed female subjects. The analysis deals with the contrasts of brain activation patterns between these two odorant conditions. The results showed a significant recruitment of the right insular cortex, and bilaterally in the cingulate in response to the trigeminal component. These findings are discussed in relation to the characteristics of these odorants compared with those tested in previous studies. Hum Brain Mapp, 2009.

Ambient odors modulate visual attentional capture

Sudden visual events capture attention involuntarily because they may signal potential threats. Some theoretical accounts consider that the biological significance of these events is established through the limbic structures. Thus, the manipulation of the limbic activity would affect attentional capture. Since these structures are directly linked to the olfactory system, we have tended to modulate their activity with olfactory stimulations. We have examined behavioral performance in a task of attentional capture by luminance under conditions of ambient odors. Our results show that attentional capture is indeed modulated by ambient odors, and that this modulation may depend on the odors properties.

Olfactory Dysfunction in Multiple Sclerosis: Evidence of a Decrease in Different Aspects of Olfactory Function

Background/Aims: Numerous authors have described olfactory dysfunction in multiple sclerosis (MS) in recent years. The aim of this study was to specify the aspects of olfactory perception that are most affected and to identify any correlations with clinical, anatomical and functional data. Methods: 50 patients with remitting or secondary progressive MS were included. Personal data were collected (medical history, characteristics of their disease, depression and disability scores and number of lesions on cerebral imaging). An olfactory test (Sniffin Sticks®) was used to evaluate subjects’ olfactory function. Results: The odor detection threshold is the most sensitive marker, with 40% of patients presenting hyposmia. The ability to identify odors is affected later on, and is inversely correlated with the level of disability. Conclusion: Our results confirm that several aspects of olfactory function are altered in MS, particularly those aspects requiring greater cognitive involvement, such as discrimination and identification of odors.

The behavioural sequences in the communication system between the child and his pet dog

Abstract This study is based on the analysis of video films of spontaneous actions between children from 2 to 5 years of age and their pet dog ( N = 20), and presents behavioural sequences which regulate the interactions between the child and his dog. The preliminary results indicate and compare the percentages of the different communication behaviours of the child and dog, and the behavioural modifications which followed. The discussion deals with the originality of the child-dog communication systems as compared with the relational systems of a young child with his peers.

Children and their pet dogs : How they communicate

The research of ethologists has provided a better understanding of the mechanisms, role and development of communication behaviour between young children and their peers. However, little is known about the communication systems between children and their pets. A study of these relational systems would be needed to understand how the child interacts with his whole environment. The present study is based on the analysis of video tapes filmed during spontaneous interactions between children from 2 to 5 years of age with their pet dog (N = 45) in their home environment. Inventories were made of the child and dog behaviours during these interactions. The results have shown the different dog behaviours induced by the child and the different child behaviours induced by the dog. The links between these behaviours and the variables which characterize both partners (age, sex, etc.) were treated by factor analysis of correspondences. These data are discussed in relation to the behavioural inventories of children and dogs with their peers and conspecifics.

The role of the amygdala in the perception of positive emotions: an “intensity detector”

The specific role of the amygdala remains controversial even though the development of functional imaging techniques has established its implication in the emotional process. The aim of this study was to highlight the sensitivity of the amygdala to emotional intensity (arousal). We conducted an analysis of the modulation of amygdala activation according to variation in emotional intensity via an fMRI event-related protocol. Monitoring of electrodermal activity, a marker of psychophysiological emotional perception and a reflection of the activation of the autonomic nervous system, was carried out concurrently. Eighteen subjects (10 men; aged from 22 to 29 years) looked at emotionally positive photographs. We demonstrated that the left and right amygdalae were sensitive to changes in emotional intensity, activating more in response to stimuli with higher intensity. Furthermore, electrodermal responses were more frequent for the most intense stimuli, demonstrating the concomitant activation of the autonomic nervous system. These results highlight the sensitivity of the amygdala to the intensity of positively valenced visual stimuli, and in conjunction with results in the literature on negative emotions, reinforce the role of the amygdala in the perception of intensity.