Biomedical subjects

Gérard Brand

Publications and source records attributed to Gérard Brand.

8 recordsLinked to original sources

PubMed2006

Olfactory/trigeminal interactions in nasal chemoreception.

For a long time, studies devoted to intranasal chemoreception have separately considered the different systems which coexist in the human nasal cavity, especially the olfactory and trigeminal systems. For the former, the findings have contributed to a better understanding of transduction, perception and the treatment of odors. For the latter, data have contributed to the knowledge of somatosensory innervation into the nose, especially in relation to nociception. During the last two decades, an increasing number of studies focused on interactions occurring between both systems. Indeed, most odorant molecules have the propensity to simultaneously stimulate olfactory and trigeminal systems in the nasal cavity. The interactions between both systems appear complex and take place at peripheral, central or perceptual levels. Studies in neurobiology, electrophysiology, psychophysics or functional imaging contribute to determine how both olfactory and trigeminal systems coexist and how one system could influence the other in the treatment of sensory information. However, several structural, functional and methodological questions remain unsolved in the field of olfactory/trigeminal interactions and deserve further research.

Animals↗

PubMed2005

Ambient odors influence the amplitude and time course of visual distraction.

Behavioral performance was examined in a task of attentional capture by luminance under conditions of ambient odors (phenyl ethyl alcohol [PEA], olfactory stimulus, and allyl isothiocyanate [AIC], mixed olfactory/trigeminal stimulus). The AIC increased the amplitude and duration of capture, whereas the presence of PEA led capture to disappear. Furthermore, the PEA caused a general slowing in the speed of information processing. The amplitude and time course of capture were correlated to the irritating components of these odorants, whereas a control experiment showed that the general slowing caused by the PEA was correlated to a drop-off of the subjects' arousal level. These results suggest that ambient odors may exert differential influence of visual-attentional processes and that this influence may depend on the odor's properties.

Adult↗

PubMed2005

Trigeminal sensitization and desensitization in the nasal cavity: a study of cross interactions.

Chemical irritation in the human nasal cavity is poorly documented. In this field, an important issue concerns the differential responses produced by successive stimulation. Repeated identical chemical irritant stimuli can produce increases or decreases in responses (two phenomena known as self-sensitization or self-desensitization). In the same way, different molecules can interact and produce cross-sensitization or cross-desensitization. The aim of this study was to contribute to this question using two specific molecules, acetic acid (AA) and allyl isothiocyanate (AIC). As the self-sensitization and -desensitization for AIC is known, a first experiment in the present work investigated the response, acute effects and time course of sensitization or desensitization to acetic acid. A second experiment tested the responses of acetic acid after a previous stimulation with allyl isothiocyanate (mustard oil) and inversely with a short inter-stimulus interval (ISI of 45 s). A third experiment similar to the second used a long inter-stimulus interval (ISI of 3 min 30). Twelve healthy subjects participated in the study using psychophysical (intensity ratings) and psychophysiological (skin conductance response) measurements. Firstly, the results showed that repeated nasal stimulation with acetic acid produced a self-desensitization whatever the ISI. Secondly, the results showed a cross-desensitization of allyl isothiocyanate by previous acetic acid stimulation. In contrast, previous stimulation with allyl isothiocyanate had no effect on the following acetic acid response. These findings confirm that trigeminal sensitization and desensitization in the nasal cavity do not follow the same processes in relation to molecules used.

Acetic Acid↗

PubMed2004

Unconscious odor detection could not be due to odor itself.

Unconscious odor detection has been demonstrated but the mechanisms implied in this process have been poorly studied. In so far, most odorants activate both olfactory and trigeminal systems, it is relevant to explore how each system could be involved in the unconscious detection processes. This study used three methods to determine the detection thresholds for three odorants. The results showed that (1). psychophysical were lower than self-evaluated thresholds whatever the odorant; (2). an odorant with trigeminal component had the ability to produce an autonomic (skin conductance response-SCR) activation with lower concentrations than psychophysical and self-evaluated thresholds; on the contrary, an odorant, which stimulates only the olfactory system, induces an autonomic activation only with higher concentrations than psychophysical and self-evaluated thresholds. These findings suggest that unconscious odor detection could be due to the trigeminal component of odorants.

Adult↗

PubMed2004

Influence of nasal trigeminal stimuli on olfactory sensitivity.

In the nose, the capacity to detect and react to volatile chemicals is mediated by two separate but interrelated sensory pathways, the olfactory and trigeminal systems. Because most chemosensory stimulants, at sufficient concentration, produce both olfactory and trigeminal sensations (i.e., stinging, burning or pungent), it is relevant to seek how these anatomically distinct systems could interact. This study was designed to evaluate by psychophysical measurements the modifications of the olfactory sensitivity of 20 subjects to phenyl ethyl alcohol (PEA) and butanol (BUT), after trigeminal stimulation with allyl isothiocyanate (AIC). Thresholds obtained in two separate sessions, one with and the other without previous trigeminal stimulation, were compared using a two-alternative forced-choice procedure, with a classical ascending concentrations method. The results showed that, whatever the odorant (PEA or BUT), AIC trigeminal activation produced a decrease in the olfactory thresholds, corresponding to an increase in olfactory sensitivity. These data confirm that in physiological conditions the trigeminal system modulates the activity of olfactory receptor cells but do not exclude the possibility of a central modulation of olfactory information by trigeminal stimuli. These findings are discussed in terms of methodological and physiological conditions.

Adult↗

PubMed2004

Left:right differences in psychophysical and electrodermal measures of olfactory thresholds and their relation to electrodermal indices of hemispheric asymmetries.

The study of lateralization processes in olfaction in human subjects has given rise to many contradictory findings. Indeed, sensorial cerebral asymmetry in olfaction depends on several factors (nature of task, quality of stimulus, characteristics of subjects, etc.) and could be also related to differences between the nostrils. In this field, few studies have assessed simultaneously the left-right nostril differences and the hemispheric asymmetry. The present work dealt with this question in the same population with the same odorants, procedures, and stimulations. Seven different concentrations of four specific odorants (two pleasant and two unpleasant) were used by single nostril stimulation with 30 dextral subjects (20 women and 10 men). Threshold detection in unilateral stimulation was investigated using electrodermal response to confirm the first psychophysic measure. Moreover, bilateral recordings of electrodermal activity (EDA) with unilateral stimulation were used as a measure of functional hemispheric asymmetry. Analysis showed no differences between the two nostrils for the threshold detection regardless of the method used (psychophysic or EDA response). However, most subjects presented a constant direction of electrodermal asymmetry whichever nostril was stimulated and whichever odorant stimulus used. The constant bilateral differences in EDA recordings are discussed in terms of asymmetrical activation of the hemispheres.

Adult↗

PubMed2003

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 odor's properties.

Adult↗

PubMed2002

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.

Acoustic Stimulation↗