Age-related differences in perception and coding of attractive odorants in mice

Hedonic perception deeply changes with aging, significantly impacting health and quality of life in elderly. In young adult mice, an odor hedonic signature is represented along the antero-posterior axis of olfactory bulb, and transferred to the olfactory tubercle and ventral tegmental area, promoting approach behavior. Here, we show that while the perception of unattractive odorants was unchanged in older mice (22 months), the appreciation of some but not all attractive odorants declined. Neural activity in the olfactory bulb and tubercle of older mice was consistently altered when attraction to pleasant odorants was impaired while maintained when the odorants kept their attractivity. Finally, in a self-stimulation paradigm, optogenetic stimulation of the olfactory bulb remained rewarding in older mice even without ventral tegmental area's response to the stimulation. Aging degrades behavioral and neural responses to some pleasant odorants but rewarding properties of olfactory bulb stimulation persisted, providing new insights into developing novel olfactory training strategies to elicit motivation even when the dopaminergic system is altered as observed in normal and/or neurodegenerative aging.

Disgusting odors trigger the oral immune system

Recent research has characterized the behavioral defense against disease. In particular the detection of sickness cues, the adaptive reactions (e.g. avoidance) to these cues and the mediating role of disgust have been the focus. A presumably important but less investigated part of a behavioral defense is the immune system response of the observer of sickness cues. Odors are intimately connected to disease and disgust, and research has shown how olfaction conveys sickness cues in both animals and humans. This study aims to test whether odorous sickness cues (i.e. disgusting odors) can trigger a preparatory immune response in humans. We show that subjective and objective disgust measures, as well as TNFα levels in saliva increased immediately after exposure to disgusting odors in a sample of 36 individuals. Altogether, these results suggest a collaboration between behavioral mechanisms of pathogen avoidance in olfaction, mediated by the emotion of disgust, and mechanisms of pathogen elimination facilitated by inflammatory mediators. Disgusting stimuli are associated with an increased risk of infection. We here test whether disgusting odors, can trigger an immune response in the oral cavity. The results indicate an increase level of TNFα in the saliva. This supports that disease cues can trigger a preparatory response in the oral cavity.

Subjective-Physiological Coherence during Food Consumption in Older Adults

BACKGROUND

Subjective-physiological emotional coherence is thought to be associated with enhanced well-being, and a relationship between subjective-physiological emotional coherence and superior nutritional status has been suggested in older populations. However, no study has examined subjective-physiological emotional coherence among older adults while tasting food. Accordingly, the present study compared subjective-physiological emotional coherence during food consumption among older and younger adults.

METHODS

Participants consumed bite-sized gel-type foods with different flavors and provided their subjective ratings of the foods while their physiological responses (facial electromyography (EMG) of the corrugator supercilia, masseter, and suprahyoid, and other autonomic nervous system signals) were simultaneously measured.

RESULTS

Our primary findings were that (1) the ratings of liking, wanting, and valence were negatively correlated with corrugator EMG activity in older and young adult participants; (2) the positive association between masseter EMG activity and ratings of wanting/valence was weaker in the older than in the young adult group; and (3) arousal ratings were negatively correlated with corrugator EMG activity in the older group only.

CONCLUSIONS

These results demonstrate commonalities and differences in subjective-physiological emotional coherence during food intake between older and young adults.

A systematic review of physiological responses to odours with a focus on current methods used in event-related study designs

OBJECTIVES

In odour research, there is still a lack of knowledge regarding the detailed understanding of the determinants and the magnitude of an odour's impact on human psychophysiology. Therefore, the present review aims to summarize current evidence on psychophysiological responses to olfactory events, to highlight diversity in research methods, and to provide recommendations for further research.

MATERIAL AND METHODS

Predefined search items were used for literature research in two databases, focussing on recent investigations of cardiac and electrodermal responses to short (<10 s) olfactory stimulations, combined with self-reports on odour experience, in a healthy population. The selected 27 publications were evaluated with regard to their methods and their findings on psychophysiological correlates of odour stimulation, following a conceptual scheme proposing mediating and moderating factors of physiological responses to odour stimuli.

RESULTS

The cardiac and electrodermal activity generally followed a discriminative pattern depending on the perceived pleasantness of an odour. Moreover, the trigeminal aspect of an odour stimulus became evident in electrodermal activity in several studies. Finally, for many of the here addressed potentially mediating and moderating variables, initial findings were obtained in some studies but these await corroboration by future research. With regard to the applied methodology, the reviewed studies were highly diverse, in terms of odour application, study design, and analysis of the time series data.

CONCLUSIONS

Future research is needed to advance our understanding of, and theoretical concepts beyond, psychophysiological responses to olfactory events, and to achieve experimentally validated methodological guidelines for psychophysiological measurements in olfaction research.

Changes in Motor Skills, Sensory Profiles, and Cognition Drive Food Selection in Older Adults With Preclinical Dysphagia

Purpose Self-selection and self-avoidance of certain foods is one possible indicator of preclinical (prior to any clinical intervention) dysphagia in healthy older adults. Self-selection of food choices is influenced by changes in a combination of factors, including neuromuscular, sensory, and individual patient characteristics. Changes to these factors occur both centrally or peripherally and can be part of typical, healthy aging. Alterations in motor, sensory, or cognitive skills may lead to self-imposed modifications to food choices and, therefore, highlight potential risk for dysphagia. Conclusions For effective screening and assessments procedures in healthy aging adults, the diagnosis of preclinical dysphagia will likely require a multifaceted assessment. A combination of assessment methods using objective and subjective measurements of neuromuscular, sensory, and individual patient factors, as well as knowledge of food avoidance, may provide insight for identifying community-dwelling older adults at risk for dysphagia and allow for earlier monitoring and intervention.

The role of hedonics in the Human Affectome

Experiencing pleasure and displeasure is a fundamental part of life. Hedonics guide behavior, affect decision-making, induce learning, and much more. As the positive and negative valence of feelings, hedonics are core processes that accompany emotion, motivation, and bodily states. Here, the affective neuroscience of pleasure and displeasure that has largely focused on the investigation of reward and pain processing, is reviewed. We describe the neurobiological systems of hedonics and factors that modulate hedonic experiences (e.g., cognition, learning, sensory input). Further, we review maladaptive and adaptive pleasure and displeasure functions in mental disorders and well-being, as well as the experience of aesthetics. As a centerpiece of the Human Affectome Project, language used to express pleasure and displeasure was also analyzed, and showed that most of these analyzed words overlap with expressions of emotions, actions, and bodily states. Our review shows that hedonics are typically investigated as processes that accompany other functions, but the mechanisms of hedonics (as core processes) have not been fully elucidated.

Putting a good face on touch: Facial expression reflects the affective valence of caress-like touch across modalities

Touch plays a central role in interpersonal behavior, especially in its capacity to convey-and induce- changes in affect. Previous research has established that slow, caress-like stroking over the skin elicits positive subjective affective responses, with higher ratings of "pleasantness" compared to a faster-moving touch stimulus. Ratings of pleasantness are associated with increased activity of a distinct class of nerve fibers: C-tactile (CT) afferents. Here, we used facial electromyography (EMG) to determine if touch that optimally activates CT afferents also influences facial muscle activity believed to reflect changes in affect. We found that less pleasant, fast-moving stroking (30 cm/s) elicited robustly negative facial EMG responses, as indexed by stronger contraction of the corrugator muscle. In contrast, pleasant, slow-moving stroking (3 cm/s) that optimally activates CT afferents resulted in decreased negative facial affective responses, manifested as significant corrugator relaxation compared to fast stroking. Moreover, the facial tracking of affective valence during touch was supra-modal, with similar effects during both directly-experienced touch and viewing of touch videos. The results of this EMG study imply that touch that fails to optimally activate CT afferent produces a negative affective response, whereas pleasant, caress-like touch has not only subjective but expressive correlates, reflected in net positive affective changes in facial expression.