Smelling odors, understanding actions

The neural substrates responsible for food odor processing: an activation likelihood estimation meta-analysis

In many species including humans, food odors appear to play a distinct role when compared with other odors. Despite their functional distinction, the neural substrates responsible for food odor processing remain unclear in humans. This study aimed to identify brain regions involved in food odor processing using activation likelihood estimation (ALE) meta-analysis. We selected olfactory neuroimaging studies conducted with sufficient methodological validity using pleasant odors. We then divided the studies into food and non-food odor conditions. Finally, we performed an ALE meta-analysis for each category and compared the ALE maps of the two categories to identify the neural substrates responsible for food odor processing after minimizing the confounding factor of odor pleasantness. The resultant ALE maps revealed that early olfactory areas are more extensively activated by food than non-food odors. Subsequent contrast analysis identified a cluster in the left putamen as the most likely neural substrate underlying food odor processing. In conclusion, food odor processing is characterized by the functional network involved in olfactory sensorimotor transformation for approaching behaviors to edible odors, such as active sniffing.

Enhancing motor imagery detection efficacy using multisensory virtual reality priming

Brain-computer interfaces (BCI) have been developed to allow users to communicate with the external world by translating brain activity into control signals. Motor imagery (MI) has been a popular paradigm in BCI control where the user imagines movements of e.g., their left and right limbs and classifiers are then trained to detect such intent directly from electroencephalography (EEG) signals. For some users, however, it is difficult to elicit patterns in the EEG signal that can be detected with existing features and classifiers. As such, new user control strategies and training paradigms have been highly sought-after to help improve motor imagery performance. Virtual reality (VR) has emerged as one potential tool where improvements in user engagement and level of immersion have shown to improve BCI accuracy. Motor priming in VR, in turn, has shown to further enhance BCI accuracy. In this pilot study, we take the first steps to explore if multisensory VR motor priming, where haptic and olfactory stimuli are present, can improve motor imagery detection efficacy in terms of both improved accuracy and faster detection. Experiments with 10 participants equipped with a biosensor-embedded VR headset, an off-the-shelf scent diffusion device, and a haptic glove with force feedback showed that significant improvements in motor imagery detection could be achieved. Increased activity in the six common spatial pattern filters used were also observed and peak accuracy could be achieved with analysis windows that were 2 s shorter. Combined, the results suggest that multisensory motor priming prior to motor imagery could improve detection efficacy.

Odor Modulates Hand Movements in a Reach-to-Grasp Task

Recent evidence suggests that target-relevant sensory stimuli (i.e., visual, auditory, and olfactory) can play important roles in the motor system. However, little is known about the effects of olfactory information on reaching and grasping movements. To determine whether odor stimuli affect hand movements, the reaching and grasping kinematic characteristics of 29 human participants were recorded using a three-dimensional video motion capture system. Participants received an odor stimulus by Sniffin’ Sticks and then reached toward and grasped a target. Grasping targets were apple, orange, ginger, and garlic. The odor stimulus was congruent with the target. The size of the odor-cued object (OCO) was the same size, smaller, or larger than a target to be grasped; or participants received odorless air while they viewed that target. They reached the target with one of two grips: a precision grip for a small target or a power grip for a larger target. The visual feedback was lost in half of 80 total trials after a start signal. It was no longer visible when participants reached the target. The results of repeated-measures analyses of variance followed by simple-effects analyses showed that when the size of the hand movement evoked by the odor cue was congruent with the size of the target, either both small or both large, the reaction time was significantly shorter than it was for odorless air. When participants received visual feedback throughout the trial, movement duration was significantly shorter if the odor cue was congruent with the size of the target or if odorless air was dispensed. When the size of hand movement evoked by the odor cue was incongruent with the size of the target, an interference effect was apparent on the maximum aperture time. The result of odorless air control group in a closed loop was shorter than incongruent odor group. In addition, visual feedback influenced the results such that the maximum aperture time occurred later when visibility was blocked only in the odorless air control condition. These results suggest that olfactory information has a positive effect on reach-to-grasp hand movements and that vision and olfaction may interact to optimize motor behavior.

Task-irrelevant odours affect both response inhibition and response readiness in fast-paced Go/No-Go task: the case of valence

Whether emotional stimuli influence both response readiness and inhibition is highly controversial. Visual emotional stimuli appear to interfere with both under certain conditions (e.g., task relevance). Whether the effect is generalisable to salient yet task-irrelevant stimuli, such as odours, remains elusive. We tested the effect of orthonasally-presented pleasant (orange) and unpleasant odours (trimethyloxazole and hexenol) and clean air as a control on response inhibition. In emotional Go/No-Go paradigms, we manipulated the intertrial interval and ratios of Go/No-Go trials to account for motor (Experiment 1, N = 31) and cognitive (Experiment 2, N = 29) response inhibition processes. In Experiment 1, participants had greater difficulty in withholding and produced more accurate and faster Go responses under the pleasant vs. the control condition. Faster Go responses were also evident in the unpleasant vs. the control condition. In Experiment 2, neither pleasant nor unpleasant odours modulated action withholding, but both elicited more accurate and faster Go responses as compared to the control condition. Pleasant odours significantly impair action withholding (as compared to the control condition), indicating that more inhibitory resources are required to elicit successful inhibition in the presence of positive emotional information. This modulation was revealed for the motor aspect of response inhibition (fast-paced design with lower Go/No-Go trial ratio) rather than for attentional interference processes. Response readiness is critically impacted by the emotional nature of the odour (but not by its valence). Our findings highlight that the valence of task-irrelevant odour stimuli is a factor significantly influencing response inhibition.

Functional MRI as an Objective Measure of Olfaction Deficit in Patients with Traumatic Anosmia

BACKGROUND AND PURPOSE

While posttraumatic anosmia is not uncommon, the olfactory function evaluation has strongly relied on subjective responses given by patients. We aimed to examine the utility of fMRI as an objective tool for diagnosing traumatic anosmia.

MATERIALS AND METHODS

Sixteen patients (11 men and 5 women; mean age, 42.2 ± 10.4 years) with clinically diagnosed traumatic anosmia and 19 healthy control subjects (11 men and 8 women; mean age, 29.3 ± 8.5 years) underwent fMRI during olfactory stimulation with citral (a pleasant odor) or β-mercaptoethanol (an unpleasant odor). All patients were subjected to a clinical olfactory functional assessment and nasal endoscopic exploration. Two-sample t tests were conducted with age as a covariate to examine group differences in brain activation responses to olfactory stimulation (false discovery rate-corrected P < .05).

RESULTS

Compared with healthy control subjects, patients with traumatic anosmia had reduced activation in the bilateral primary and secondary olfactory cortices and the limbic system in response to β-mercaptoethanol stimulation, whereas reduced activation was observed only in the left frontal subgyral region in response to citral stimulation.

CONCLUSIONS

Brain activation was decreased in the bilateral primary and secondary olfactory cortices as well as the limbic system in response to olfactory stimulation in patients with traumatic anosmia compared with healthy control subjects. These preliminary results may shed light on the potential of fMRI for the diagnosis of traumatic anosmia.

Empathic Cognitions Affected by Undetectable Social Chemosignals: An EEG Study on Visually Evoked Empathy for Pain in an Auditory and Chemosensory Context

Reduction of mu activity within the EEG is an indicator of cognitive empathy and can be generated in response to visual depictions of others in pain. The current study tested whether this brain response can be modulated by an auditory and a chemosensory context. Participants observed pictures of painful and non-painful actions while pain associated and neutral exclamations were presented (Study 1, N = 30) or while chemosensory stimuli were presented via a constant flow olfactometer (Study 2, N = 22). Chemosensory stimuli were sampled on cotton pads while donors participated in a simulated job interview (stress condition) or cycled on a stationary bike (sport condition). Pure cotton was used as a control. The social chemosignals could not be detected as odors. Activity within the 8–13 Hz band at electrodes C3, C4 (mu activity) and electrodes O1, O2 (alpha-activity) was calculated using Fast-Fourier-Transformation (FFT). As expected, suppression of power in the 8–13 Hz band was stronger when painful as compared to non-painful actions were observed (Study 1, p = 0.020; Study 2, p = 0.005). In addition, as compared to the neutral auditory and chemosensory context, painful exclamations (Study 1, p = 0.039) and chemosensory stress signals (Study 2, p = 0.014) augmented mu-/alpha suppression also in response to non-painful pictures. The studies show that processing of social threat-related information is not dominated by visual information. Rather, cognitive appraisal related to empathy can be affected by painful exclamations and subthreshold chemosensory social information.

Translating novel findings of perceptual-motor codes into the neuro-rehabilitation of movement disorders

The bidirectional flow of perceptual and motor information has recently proven useful as rehabilitative tool for re-building motor memories. We analyzed how the visual-motor approach has been successfully applied in neurorehabilitation, leading to surprisingly rapid and effective improvements in action execution. We proposed that the contribution of multiple sensory channels during treatment enables individuals to predict and optimize motor behavior, having a greater effect than visual input alone. We explored how the state-of-the-art neuroscience techniques show direct evidence that employment of visual-motor approach leads to increased motor cortex excitability and synaptic and cortical map plasticity. This super-additive response to multimodal stimulation may maximize neural plasticity, potentiating the effect of conventional treatment, and will be a valuable approach when it comes to advances in innovative methodologies.

Body and Odors

Interpersonal interactions are primarily mediated through vision. However, crucial information concerning other individuals is also captured through different senses. New evidence suggests that body odors can implicitly initiate, filter, and guide the integrated perceptions that characterize real human impressions. Human body-odor processing helps rapidly differentiate kin from friends and friends from foes, as well as identify potential threats or increase alertness to the proximity of strangers, thereby guiding social preference. Body odors, which are potent sources of discriminative, affective, and motor knowledge, elicit neural activity partly or exclusively outside the primary olfactory cortices in the brain areas responsible for the processing of social information, which are activated by equivalent visual signals. Body odors, which can act as an authenticator of truth and are reliably invoked to shape social relations, require us to revise our view of the traditional body-communication models.

Superior orthonasal but not retronasal olfactory skills in congenital blindness

Sight is undoubtedly important for finding and appreciating food, and cooking. Blind individuals are strongly impaired in finding food, limiting the variety of flavours they are exposed to. We have shown before that compared to sighted controls, congenitally blind individuals have enhanced olfactory but reduced taste perception. In this study we tested the hypothesis that congenitally blind subjects have enhanced orthonasal but not retronasal olfactory skills. Twelve congenitally blind and 14 sighted control subjects, matched in age, gender and body mass index, were asked to identify odours using grocery-available food powders. Results showed that blind subjects were significantly faster and tended to be better at identifying odours presented orthonasally. This was not the case when odorants were presented retronasally. We also found a significant group x route interaction, showing that although both groups performed better for retronasally compared to orthonasally presented odours, this gain was less pronounced for blind subjects. Finally, our data revealed that blind subjects were more familiar with the orthonasal odorants and used the retronasal odorants less often for cooking than their sighted counterparts. These results confirm that orthonasal but not retronasal olfactory perception is enhanced in congenital blindness, a result that is concordant with the reduced food variety exposure in this group.

Facilitation of action planning in children with autism: the contribution of the maternal body odor

Imitation is a key socio-cognitive skill impaired in individuals with Autism Spectrum Conditions (ASC). It is known that the familiarity with an actor facilitates the appearance of imitative abilities. Here, we explore whether a highly familiar and socially relevant stimulus presented in the olfactory modality is able to improve spontaneous imitation as early as at the level of action planning. A group of 20 children with ASC and 20 controls observed their own mother or the mother of another child performing a reach-to-grasp action towards an object, under the exposure to their maternal odor, the odor of the mother of another child or no odor. Subsequently, children acted upon the same object with no specific instruction to imitate. Child's movement initiation time (MIT) served as an indicator of motor planning facilitation induced by action observation. Results suggest that for children with ASC (but not controls) MIT was significantly lower when exposed to the maternal odor both when interacting with a familiar or an unfamiliar model. In the former case, the performance is comparable to controls. The familiar model in the absence of any olfactory cue is able to induce a facilitation effect, but the maximal facilitation on MIT is evident when maternal odor and familiar model are paired. We hypothesize that for children with ASC the maternal odor provides relevant social motivation for taking advantage of others' actions when planning movements in an imitative context.

Eating tools in hand activate the brain systems for eating action: a transcranial magnetic stimulation study

There is increasing neuroimaging evidence suggesting that visually presented tools automatically activate the human sensorimotor system coding learned motor actions relevant to the visual stimuli. Such crossmodal activation may reflect a general functional property of the human motor memory and thus can be operating in other, non-limb effector organs, such as the orofacial system involved in eating. In the present study, we predicted that somatosensory signals produced by eating tools in hand covertly activate the neuromuscular systems involved in eating action. In Experiments 1 and 2, we measured motor evoked response (MEP) of the masseter muscle in normal humans to examine the possible impact of tools in hand (chopsticks and scissors) on the neuromuscular systems during the observation of food stimuli. We found that eating tools (chopsticks) enhanced the masseter MEPs more greatly than other tools (scissors) during the visual recognition of food, although this covert change in motor excitability was not detectable at the behavioral level. In Experiment 3, we further observed that chopsticks overall increased MEPs more greatly than scissors and this tool-driven increase of MEPs was greater when participants viewed food stimuli than when they viewed non-food stimuli. A joint analysis of the three experiments confirmed a significant impact of eating tools on the masseter MEPs during food recognition. Taken together, these results suggest that eating tools in hand exert a category-specific impact on the neuromuscular system for eating.

Body odors promote automatic imitation in autism

BACKGROUND

Autism spectrum disorders comprise a range of neurodevelopmental pathologies characterized, among other symptoms, by impaired social interactions. Individuals with this diagnosis are reported to often identify people by repetitively sniffing pieces of clothing or the body odor of family members. Since body odors are known to initiate and mediate many different social behaviors, smelling the body odor of a family member might constitute a sensory-based action promoting social contact. In light of this, we hypothesized that the body odor of a family member would facilitate the appearance of automatic imitation, an essential social skill known to be impaired in autism.

METHODS

We recruited 20 autistic and 20 typically developing children. Body odors were collected from the children's mothers' axillae. A child observed a model (their mother or a stranger mother) execute (or not) a reach-to-grasp action toward an object. Subsequently, she performed the same action. The object was imbued with the child's mother's odor, a stranger mother's odor, or no odor. The actions were videotaped, and movement time was calculated post hoc via a digitalization technique.

RESULTS

Automatic imitation effects-expressed in terms of total movement time reduction-appear in autistic children only when exposed to objects paired with their own mother's odor.

CONCLUSIONS

The maternal odor, which conveys a social message otherwise neglected, helps autistic children to covertly imitate the actions of others. Our results represent a starting point holding theoretical and practical relevance for the development of new strategies to enhance communication and social behavior among autistic individuals.

Odor mental imagery in non-experts in odors: a paradox?

In agreement with the theoretical framework stipulating that mental images arise from neural activity in early sensory cortices, the primary olfactory cortex [i.e., the piriform cortex (PC)] is activated when non-olfactory-experts try to generate odor mental images. This finding strongly contrasts with the allegation that it is typically impossible to mentally imagine odors. However, other neurophysiological or cognitive processes engaged in the endeavor of odor mental imagery such as sniffing, attention, expectation, and cross-modal interactions involve the PC and could explain this paradox. To unambiguously study the odor mental imagery, we first argued the need to investigate odor experts who have learned to specifically reactivate olfactory percepts. We then assert the necessity to explore the network dedicated to this function by considering variations in both the activity level and the connection strength of the areas belonging to this network as a function of the level of expertise of the odor experts.

When flavor guides motor control: an effector independence study

Research on multisensory integration during natural tasks has revealed how chemical senses contribute to plan and control movements. An aspect which has yet to be investigated regards whether the motor representations evoked by chemosensory stimuli, once established for a particular movement, can be used to control different effectors. Here, we investigate this issue by asking participants to drink a sip of flavored solution, grasp with the hand a visual target, and then bring it to the mouth, miming the action of biting. Results show that hand and lip apertures were scaled according to the size of the object evoked by the flavor. Maximum hand and lip apertures were greater when the action toward a small visual target (e.g., strawberry) was preceded by a sip of a "large" (e.g., orange) than a "small" (e.g., almond) flavor solution. Conversely, maximum hand and lip apertures were smaller when the action toward a large visual target (e.g., apple) was preceded by the presentation of a "small" (e.g., strawberry) rather than a "large" flavor solution. These findings support previous evidence on the presence of a unique motor plan underlying the act of grasping with-the-hand and with-the-mouth, extending the knowledge of chemosensorimotor transformations to motor equivalence.