Behavioral and Neurobiological Convergence of Odor, Mood and Emotion: A Review.

The affective state is the combination of emotion and mood, with mood reflecting a running average of sequential emotional events together with an underlying internal affective state. There is now extensive evidence that odors can overtly or subliminally modulate mood and emotion. Relying primarily on neurobiological literature, here we review what is known about how odors can affect emotions/moods and how emotions/moods may affect odor perception. We take the approach that form can provide insight into function by reviewing major brain regions and neural circuits underlying emotion and mood, and then reviewing the olfactory pathway in the context of that emotion/mood network. We highlight the extensive neuroanatomical opportunities for odor-emotion/mood convergence, as well as functional data demonstrating reciprocal interactions between these processes. Finally, we explore how the odor- emotion/mood interplay is, or could be, used in medical and/or commercial applications.

New determinants of olfactory habituation.

Habituation is a filter that optimizes the processing of information by our brain in all sensory modalities. It results in an unconscious reduced responsiveness to continuous or repetitive stimulation. In olfaction, the main question is whether habituation works the same way for any odorant or whether we habituate differently to each odorant? In particular, whether chemical, physical or perceptual cues can limit or increase habituation. To test this, the odour intensity of 32 odorants differing in physicochemical characteristics was rated by 58 participants continuously during 120s. Each odorant was delivered at a constant concentration. Results showed odorants differed significantly in habituation, highlighting the multifactoriality of habituation. Additionally habituation was predicted from 15 physico-chemical and perceptual characteristics of the odorants. The analysis highlighted the importance of trigeminality which is highly correlated to intensity and pleasantness. The vapour pressure, the molecular weight, the Odor Activity Value (OAV) and the number of double bonds mostly contributed to the modulation of habituation. Moreover, length of the carbon chain, number of conformers and hydrophobicity contributed to a lesser extent to the modulation of habituation. These results highlight new principles involved in the fundamental process of habituation, notably trigeminality and the physicochemical characteristics associated.

Reflections on the hand: the use of a mirror highlights the contributions of interpreted and retinotopic representations in the rubber-hand illusion.

In the rubber-hand illusion, observing a rubber hand stroked in synchrony with one's own hand results in mislocalisation of the own hand, which is perceived as being located closer to the rubber hand. This illusion depends on having the rubber hand placed at a plausible egocentric orientation with respect to the observer. In the present study, we took advantage of this finding in order to compare the relative influence on the illusion of the rubber hand's perceived retinotopic image against its real-world position. The rubber hand was positioned egocentrically (fingers away from the participant) or allocentrically (fingers towards the participant), while participants viewed it either directly or via a mirror that was placed facing the participant. In the mirror conditions, the orientation of the retinotopic image of the hand (either egocentric or allocentric) was opposed to its real-world orientation. We found that the illusion was elicited in both mirror conditions, to roughly the same extent. Thus either of two representations can elicit the rubber-hand illusion: a world-centred understanding of the scene, resulting from the inferred position of the hand based on its mirror reflection, or a purely visual retinotopic representation of the viewed hand. In the mirror conditions, the illusion was somewhat weaker than in the typical directly viewed egocentric condition. We attribute this to competition between two incompatible representations introduced by the presence of the mirror. Finally, in two control experiments we ruled out that this reduction was due to two properties of mirror reflections: the increased perceived distance of items and the reversal of the apparent handedness of the rubber hand.

Dissociation of extrastriate body and biological-motion selective areas by manipulation of visual-motor congruency.

To date, several posterior brain regions have been identified that play a role in the visual perception of other people and their movements. The aim of the present study is to understand how these areas may be involved in relating body movements to their visual consequences. We used fMRI to examine the extrastriate body area (EBA), the fusiform body area (FBA), and an area in the posterior superior temporal sulcus (pSTS) that responds to patterns of human biological motion. Each area was localized in individual participants with independent scans. In the main experiment, participants performed and/or viewed simple, intransitive hand actions while in the scanner. An MR-compatible camera with a near-egocentric view of the participant's hand was used to manipulate the relationship between motor output and the visual stimulus. Participants' only view of their hands was via this camera. In the Compatible condition, participants viewed their own live hand movements projected onto the screen. In the Incompatible condition, participants viewed actions that were different from the actions they were executing. In pSTS, the BOLD response in the Incompatible condition was significantly higher than in the Compatible condition. Further, the response in the Compatible condition was below baseline, and no greater than that found in a control condition in which hand actions were performed without any visual input. This indicates a strong suppression in pSTS of the response to the visual stimulus that arises from one's own actions. In contrast, in EBA and FBA, we found a large but equivalent response to the Compatible and Incompatible conditions, and this response was the same as that elicited in a control condition in which hand actions were viewed passively, with no concurrent motor task. These findings indicate that, in contrast to pSTS, EBA and FBA are decoupled from motor systems. Instead we propose that their role is limited to perceptual analysis of body-related visual input.