Prefrontal activity during flavor difference test: Application of functional near-infrared spectroscopy to sensory evaluation studies

Right prefrontal activation associated with deviations from expected lipstick texture assessed with functional near-infrared spectroscopy

Introduction

There is a continuous consumer demand for ever superior cosmetic products. In marketing, various forms of sensory evaluation are used to measure the consumer experience and provide data with which to improve cosmetics. Nonetheless, potential downsides of existing approaches have led to the exploration of the use of neuroimaging methods, such as functional near-infrared spectroscopy (fNIRS), to provide addition information about consumers' experiences with cosmetics. The aim of the present study was to investigate the feasibility of a real-time brain-based product evaluation method which detects the incongruency between a product, in this case lipstick, and a consumer's expectations.

Method

Thirty healthy, female, habitual lipstick users were asked to apply six different lipsticks varying in softness and to rate the softness of and their willingness to pay (WTP) for each lipstick. Cerebral hemodynamic responses in frontal areas were measured with fNIRS during lipstick application and analyzed using the general linear model (GLM). Incongruency scores between softness and expectation were calculated in order to understand how far removed each lipstick was from a participant's optimal softness preference. The correlation between brain activation (beta scores) during the application of each lipstick and the respective incongruency scores from each participant were acquired using semi-partial correlation analysis, controlling for the effects of WTP.

Results

We revealed a significant intra-subject correlation between incongruency scores and activation in the right inferior frontal gyrus (IFG). This confirms that as the texture incongruency scores increased for the lipstick samples, activation in each individual's right IFG also increased.

Conclusion

The correlation observed between incongruency perceived by participants and activation of the right IFG not only suggests that the right IFG may play an important role in detecting incongruity when there is a discrepancy between the perceived texture and the consumer's expectations but also that measuring activity in the IFG may provide a new objective measurement of the consumer experience, thus contributing to the development of superior cosmetics.

Discovery and verification of bitter components in Panax notoginseng based on the integrated strategy of pharmacophore model, system separation and bitter tracing technology

Panax notoginseng is a world-renowned tonic herb, which has been used as a characteristic food in Southwest China for hundreds of years. However, the taste of Panax notoginseng is extremely bitter and serious after tasting, and its bitter components are unknown. This manuscript proposes a new strategy for discovering bitter components of Panax notoginseng based on the integrated analysis of pharmacophore model, system separation and bitter tracing technology. Firstly, 16 potential bitter components were obtained by UPLC-Q-Orbitrap HRMS combined with virtual screening, most of which were saponins.Then, the bitter components were further separated by system component separation and 5 potential bitter components were obtained. Finally, the main contributors of bitterness in Panax notoginseng were verified to be Ginsenoside Rg1, Ginsenoside Rb1 and Ginsenoside Rd by components knock-in and fNIRS. In general, this paper is the first literature report on the relatively systematic study of bitter components in Panax notoginseng.

Effect of Mastication Muscle Activity on Prefrontal Cortex NIRS Measurement: A Pilot Study

Changes in NIRS signals are related to changes in local cerebral blood flow or oxy-Hb concentration. On the other hand, recent studies have revealed the effect of chewing gum on cognitive performance, stress control etc. which accompanied brain activity in the prefrontal cortex (PFC). However, these relationships are still controversial. To evaluate the chewing effect on PFC, NIRS seems to be a suitable method of imaging such results. When measuring NIRS on PFC, blood volume in superficial tissues (scalp, skin, muscle) might have some affect. The aim of the present study was to clarify the effect of the anterior temporal muscle on NIRS signals during gum chewing. Eight healthy volunteers participated. Two-channel NIRS (HOT-1000, NeU, Japan), which can distinguish total-Hb concentrations in deep tissue and superficial tissue layers, was used. In addition to a conventional optode separation distance of 3.0 cm, Hot 1000 has a short distance of 1.0 cm (NEAR channel) to measure NIRS signals that originate exclusively from surface tissues. NIRS probes were placed at Fp1 and Fp2 in the normal probe setting. The headset was displaced to the left in order to allow the left probe to be placed over the left anterior temporal muscle. In the normal setting, the superficial signal curve shows no notable change; however, the neural (calculated and defined in HOT-1000) and deep curves show an increase during the gum chewing task. At the deviated setting, all three signals show marked changes during the task. Total-Hb concentration in the deviated probe setting is significantly large (p < 0.05) than that of in the normal probe setting. When using gum chewing as a task, it would be better to consider a probe position carefully so that the influence of muscle activity on NIRS signal can be distinguished.

Activity of frontal pole cortex reflecting hedonic tone of food and drink: fNIRS study in humans

Cognitive and hedonic aspects of taste have been studied using different neuroimaging techniques in humans. However, the methods used are unsuitable for easy monitoring of hedonics induced by intake of foods and beverages. Here we have tried to monitor changes in oxygenated hemoglobin (oxyHb) levels in the anterior prefrontal cortex (aPFC, frontopolar cortex, Brodmann area 10) in response to intake of hedonically different edibles in healthy adults. When subjects tasted sweet and bitter solutions freely without any particular instruction, cortical activation varied greatly among subjects and between the two stimuli, and no consistent results were obtained. Subjects then ate or drank preferred (hedonically positive) and disliked (hedonically negative) edibles. Although these stimuli differed among subjects, hedonically positive stimuli decreased oxyHb, whereas hedonically negative stimuli increased oxyHb, particularly in the ventral aPFC. When subjects tasted 4 kinds of jellies with different flavors and evaluated the degree of pleasantness, oxyHb level in the ventral region correlated negatively with pleasantness score. These results revealed that pleasant and unpleasant edibles tended to elicit decreased and increased oxyHb levels, respectively, within the ventral aPFC, suggesting that monitoring of oxyHb in this region may prove useful for objective evaluation of pleasantness of food and drink.

Enhancement of Saltiness Perception by Monosodium Glutamate Taste and Soy Sauce Odor: A Near-Infrared Spectroscopy Study

Previous studies have reported that the umami taste of monosodium l-glutamate (MSG) and salty-smelling odors (e.g., soy sauce, bacon, sardines) enhance the perception of saltiness. This study aimed to investigate the neural basis of the enhancement of saltiness in human participants using functional near-infrared spectroscopy (fNIRS). University students who had passed a taste panel test participated in this study. Sodium chloride solutions were presented with or without either 0.10% MSG or the odor of soy sauce. The participants were asked to drink a cup of the stimulus and to evaluate only saltiness intensity in Experiment 1, as well as other sensory qualities in Experiment 2, and temporal brain activity was measured using fNIRS. In Experiment 3, the participants were asked to evaluate saltiness intensity using the time-intensity (TI) method, and the response of the parotid salivary glands was measured using fNIRS. The fNIRS data showed that the added MSG and soy sauce enhanced the hemodynamic response in temporal brain regions, including the frontal operculum, but no effect on the hemodynamic salivary responses was detected. These results indicate that the perceived enhancement of saltiness occurs in the brain region that is involved in central gustatory processing. Furthermore, the results of the sensory evaluations suggest that enhancement of saltiness by the addition of MSG is mainly based on fusion of the salty-like property of MSG and saltiness of NaCl, whereas enhancement by the addition of soy sauce odor is mainly based on modulation of the temporal dynamics of saltiness perception.

Neuroimaging and neuromodulation approaches to study eating behavior and prevent and treat eating disorders and obesity

Functional, molecular and genetic neuroimaging has highlighted the existence of brain anomalies and neural vulnerability factors related to obesity and eating disorders such as binge eating or anorexia nervosa. In particular, decreased basal metabolism in the prefrontal cortex and striatum as well as dopaminergic alterations have been described in obese subjects, in parallel with increased activation of reward brain areas in response to palatable food cues. Elevated reward region responsivity may trigger food craving and predict future weight gain. This opens the way to prevention studies using functional and molecular neuroimaging to perform early diagnostics and to phenotype subjects at risk by exploring different neurobehavioral dimensions of the food choices and motivation processes. In the first part of this review, advantages and limitations of neuroimaging techniques, such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), pharmacogenetic fMRI and functional near-infrared spectroscopy (fNIRS) will be discussed in the context of recent work dealing with eating behavior, with a particular focus on obesity. In the second part of the review, non-invasive strategies to modulate food-related brain processes and functions will be presented. At the leading edge of non-invasive brain-based technologies is real-time fMRI (rtfMRI) neurofeedback, which is a powerful tool to better understand the complexity of human brain-behavior relationships. rtfMRI, alone or when combined with other techniques and tools such as EEG and cognitive therapy, could be used to alter neural plasticity and learned behavior to optimize and/or restore healthy cognition and eating behavior. Other promising non-invasive neuromodulation approaches being explored are repetitive transcranial magnetic stimulation (rTMS) and transcranial direct-current stimulation (tDCS). Converging evidence points at the value of these non-invasive neuromodulation strategies to study basic mechanisms underlying eating behavior and to treat its disorders. Both of these approaches will be compared in light of recent work in this field, while addressing technical and practical questions. The third part of this review will be dedicated to invasive neuromodulation strategies, such as vagus nerve stimulation (VNS) and deep brain stimulation (DBS). In combination with neuroimaging approaches, these techniques are promising experimental tools to unravel the intricate relationships between homeostatic and hedonic brain circuits. Their potential as additional therapeutic tools to combat pharmacorefractory morbid obesity or acute eating disorders will be discussed, in terms of technical challenges, applicability and ethics. In a general discussion, we will put the brain at the core of fundamental research, prevention and therapy in the context of obesity and eating disorders. First, we will discuss the possibility to identify new biological markers of brain functions. Second, we will highlight the potential of neuroimaging and neuromodulation in individualized medicine. Third, we will introduce the ethical questions that are concomitant to the emergence of new neuromodulation therapies.

Distinct aging effects for two types of inhibition in older adults: a near-infrared spectroscopy study on the Simon task and the flanker task

The present study examined age-related changes in inhibitory processes among older and younger adults in the flanker and Simon tasks in terms of behavioral performance and prefrontal brain activity by functional near-infrared spectroscopy. The flanker task requires a quick identification of a central target in the presence of surrounding distracters, whereas the Simon task requires an individual to respond with left and right key presses to nonspatial features of the stimulus presented in the left and right locations. The reaction times of two age groups were longer under incongruent conditions than under congruent conditions in both tasks, indicating that the flanker effect (interference suppression) and the Simon effect (response suppression) were evident. In agreement with previous studies, the magnitude of the effect for the Simon task was greater for the older adults than for the younger adults, whereas the two groups showed equivalent flanker effects. The results suggest that older adults have difficulties in response inhibition, but not in stimulus interference suppression. Enhanced activity was found in different brain regions across the two tasks among the older adults. The older adults showed more activity in the superior and middle frontal gyri of the left hemisphere than younger adults in the flanker task; they showed more activity in the bilateral superior frontal gyri in the Simon task. These results suggest that the underlying mechanisms of the inhibition processes for the two tasks are distinct: they rely on different brain regions and have differential vulnerabilities to aging.

Neurofeedback using real-time near-infrared spectroscopy enhances motor imagery related cortical activation

Accumulating evidence indicates that motor imagery and motor execution share common neural networks. Accordingly, mental practices in the form of motor imagery have been implemented in rehabilitation regimes of stroke patients with favorable results. Because direct monitoring of motor imagery is difficult, feedback of cortical activities related to motor imagery (neurofeedback) could help to enhance efficacy of mental practice with motor imagery. To determine the feasibility and efficacy of a real-time neurofeedback system mediated by near-infrared spectroscopy (NIRS), two separate experiments were performed. Experiment 1 was used in five subjects to evaluate whether real-time cortical oxygenated hemoglobin signal feedback during a motor execution task correlated with reference hemoglobin signals computed off-line. Results demonstrated that the NIRS-mediated neurofeedback system reliably detected oxygenated hemoglobin signal changes in real-time. In Experiment 2, 21 subjects performed motor imagery of finger movements with feedback from relevant cortical signals and irrelevant sham signals. Real neurofeedback induced significantly greater activation of the contralateral premotor cortex and greater self-assessment scores for kinesthetic motor imagery compared with sham feedback. These findings suggested the feasibility and potential effectiveness of a NIRS-mediated real-time neurofeedback system on performance of kinesthetic motor imagery. However, these results warrant further clinical trials to determine whether this system could enhance the effects of mental practice in stroke patients.

Individual differences in prefrontal cortex activity during perception of bitter taste using fNIRS methodology

Although bitter taste has a crucial role in nutrition by preventing the ingestion of toxic foods, there are few studies on bitter taste neuroimaging. To identify cortical areas involved in bitter taste perception and to determine if individual differences in taste sensitivity to 6-n-propylthiouracil (PROP) are represented in the brain by different cortical activation patterns, we examined 48 healthy volunteers using functional near-infrared spectroscopy. Participants rated the perceived intensity of filter paper disks impregnated with PROP and NaCl during the imaging procedure and were then classified as PROP tasters and nontasters. We monitored cortical activity in both the anterior and posterior regions of the dorsolateral prefrontal cortex (DLPFC) and in the ventrolateral prefrontal cortex (VLPFC). No activity was detected in the anterior DLPFC in any of the participants. However, during the administration of PROP, significant cortical activation was detected in the more posterior regions of the left DLPFC and in the left and right VLPFC but only in PROP tasters. PROP nontasters showed no cortical activity in these areas. These data suggest that the prefrontal cortex is involved in the conscious perception of the bitter taste of PROP and that the pattern of activity is consistent with individual differences in the ability to taste this compound. Thus, the PROP phenotype is associated with fundamental differences in cortical taste processing.

How do infants perceive scrambled face?: A near-infrared spectroscopic study

Using near-infrared spectroscopy (NIRS), we recorded changes of oxy-Hb, deoxy-Hb, and total-Hb in 7- to 8-month-old infants' and adults' brains in response to canonical face and scrambled face stimuli. Using a newly developed probe for NIRS recording, which was light and soft enough to be tolerated by infants, we were able to acquire data from the very young even in the awake state. Total-Hb in response to a canonical face stimulus was greater than for scrambled face stimuli only in the right hemisphere in infants. This indicates the presence of right hemisphere dominance of brain activity in response to face images in 7- to 8-month-old infants. In adults, oxy-Hb and total-Hb were significantly increased from baseline only for the canonical face in the right hemisphere. There were greater numbers of channels showing significantly increased activity for the canonical face in the right than in the left hemisphere. These data indicate that the right hemisphere is more dominant for canonical face perception in both infants and adults. However, overall, the increase of total-Hb and oxy-Hb in adults was modest compared to infants. Although the reason for the difference between infants and adults is unclear, in addition to developmental changes influencing face perception, some methodological problems may be present. Thus, because we recorded NIRS signals in infants and adults using the same method, anatomical and physiological problems might affect the results to some degree. Although comparing the results between infants and adults is not simple, the present study is the first to indicate how 7- to 8-month-old infants perceive scrambled face stimuli and to compare such results with those of adults in order to understand developmental changes in face perception.

Shift of motor activation areas during recovery from hemiparesis after cerebral infarction: a longitudinal study with near-infrared spectroscopy

Motor functional recovery after stroke may be attributable to cerebral reorganization. We used near-infrared spectroscopy, which measures non-invasively the changes in oxy- and deoxy-hemoglobin concentrations in response to neural activation, for monitoring cerebral activation in stroke patients, and investigated the longitudinal changes in functional laterality of activations in the primary sensorimotor cortex during unilateral audio-paced (1 Hz) hand movement. We examined five ischemic stroke patients (4 females and 1 male, 52-67 years old) with mild to moderate hemiparesis at acute stages and chronic stages at least 1 month later. Normal subjects (3 females and 2 males, 47-63 years old) were also included. Unilateral hand movement activated predominantly the contralateral primary sensorimotor cortex in the normal subjects and the stroke patients when they moved unaffected hand. Affected hand movements activated bilateral sensorimotor cortices early after stroke (< 25 days of stroke onset), whereas the activation pattern returned toward normal at later periods (> 35 days). The contralaterality index (0.34 +/- 0.12 in normal control) was reduced at early periods (0.00 +/- 0.03, p < 0.01) after stroke, and returned to normal (0.35 +/- 0.24) as motor function recovered. These findings suggest that a transient increase in motor activation in the ipsilateral intact hemisphere within 1 month may play an important role in the recovery from motor dysfunction after stroke.

Virtual spatial registration of stand-alone fNIRS data to MNI space

The registration of functional brain data to common stereotaxic brain space facilitates data sharing and integration across different subjects, studies, and even imaging modalities. Thus, we previously described a method for the probabilistic registration of functional near-infrared spectroscopy (fNIRS) data onto Montreal Neurological Institute (MNI) coordinate space that can be used even when magnetic resonance images of the subjects are not available. This method, however, requires the careful measurement of scalp landmarks and fNIRS optode positions using a 3D-digitizer. Here we present a novel registration method, based on simulations in place of physical measurements for optode positioning. First, we constructed a holder deformation algorithm and examined its validity by comparing virtual and actual deformation of holders on spherical phantoms and real head surfaces. The discrepancies were negligible. Next, we registered virtual holders on synthetic heads and brains that represent size and shape variations among the population. The registered positions were normalized to MNI space. By repeating this process across synthetic heads and brains, we statistically estimated the most probable MNI coordinate values, and clarified errors, which were in the order of several millimeters across the scalp, associated with this estimation. In essence, the current method allowed the spatial registration of completely stand-alone fNIRS data onto MNI space without the use of supplementary measurements. This method will not only provide a practical solution to the spatial registration issues in fNIRS studies, but will also enhance cross-modal communications within the neuroimaging community.

Exploring the false discovery rate in multichannel NIRS

Near infrared spectroscopy (NIRS), an emerging non-invasive tool for functional neuroimaging, has evolved as a multichannel technique allowing simultaneous measurements through many channels ranging from below ten to above hundred. Simultaneous testing of such a large number of channels escalates the risk of Type I error, therefore multiplicity correction is unavoidable. To date, only a few studies have considered this issue using Bonferroni correction, which is an effective conservative solution, but may be too severe for neuroimaging. Its power varies in inverse proportion of the number of channels, which varies among NIRS studies depending on selected region of interest (ROI), thereby leading to a subjective inference. This problem may be well circumvented by a more contemporary approach, called false discovery rate (FDR) that is widely being adopted in functional neuroimaging. An FDR-based procedure controls the expected proportion of erroneously rejected hypotheses among the rejected hypotheses, which offers a more objective, powerful, and consistent measure of Type I error than Bonferroni correction and maintains a better balance between power and specificity. In this technical note, we examine FDR approach using examples from simulated and real NIRS data. The FDR-based procedure could yield 52% more power than Bonferroni correction in a 172-channel real NIRS study and proved to be more robust against the changing number of channels.