Prefrontal activation through task requirements of emotional induction measured with NIRS

Stress estimation by the prefrontal cortex asymmetry: Study on fNIRS signals

BACKGROUND

Functional near-infrared spectroscopy (fNIRS) is a non-invasive technique frequently used to measure the brain hemodynamic activity in applications to evaluate affective disorders and stress. Using two wavelengths of light, it is possible to monitor relative changes in the concentrations of oxyhemoglobin and deoxyhemoglobin. Besides, the spatial asymmetry in the prefrontal cortex activity has been correlated with the brain response to stressful situations.

METHODS

We measured prefrontal cortex activity with a NIRS multi-distance device during a baseline period, under stressful conditions (e.g., social stress), and after a recovery phase. We calculated a laterality index for the contaminated brain signal and for the brain signal where we removed the influence of extracerebral hemodynamic activity by using a short channel.

RESULTS

There was a significant right lateralization during stress when using the contaminated signals, consistent with previous investigations, but this significant difference disappeared using the corrected signals. Indeed, exploration of the susceptibility to contamination of the different channels showed non-homogeneous spatial patterns, which would hint at detection of stress from extracerebral activity from the forehead.

LIMITATIONS

There was no recovery phase between the social and the arithmetic stressor, a cumulative effect was not considered.

CONCLUSIONS

Extracerebral hemodynamic activity provided insights into the pertinence of short channel corrections in fNIRS studies dealing with emotions. It is important to consider this issue in clinical applications including modern monitoring systems based on fNIRS technique to assess emotional states in affective disorders.

Similarities and differences in the induction and regulation of the negative emotions fear and disgust: A functional near infrared spectroscopy study

Affective processing, including induction and regulation of emotion, activates neural networks, induces physiological responses, and generates subjective experience. Dysregulation of these processes can lead to maladaptive behavior and even psychiatric morbidity. Multimodal studies of emotion thus not only help elucidate the nature of emotion, but also contribute to important clinical insights. In the present study, we compared the induction (EI) and effortful regulation (ER) with reappraisal of fear and disgust in healthy subjects using functional near infrared spectroscopy (fNIRS) in conjunction with electrodermal activity (EDA). During EI, there was significant activation in medial prefrontal cortex (PFC) for fear and more widespread activation for disgust, with right lateral PFC significantly more active during disgust compared to fear. ER was equally effective for fear and disgust reducing subjective emotion rating by roughly 45%. Compared to baseline, there was no increased PFC activity for fear during ER, while for disgust lateral PFC was significantly more active. Significant differences between the two negative emotions were also observed in sympathetic nerve activity as reflected in EDA during EI, but not during ER. Lastly, compared to men, women had higher emotion rating for both fear and disgust without corresponding differences in EDA. In conclusion, in the present study we show that emotion induction was associated with differential activation in both PFC and sympathetic nerve activity for fear and disgust. These differences were however less prominent during emotion regulation. We discuss the potential interpretation of our results and their implications regarding our understanding of negative emotion processing.

A pediatric near-infrared spectroscopy brain-computer interface based on the detection of emotional valence

Brain-computer interfaces (BCIs) are being investigated as an access pathway to communication for individuals with physical disabilities, as the technology obviates the need for voluntary motor control. However, to date, minimal research has investigated the use of BCIs for children. Traditional BCI communication paradigms may be suboptimal given that children with physical disabilities may face delays in cognitive development and acquisition of literacy skills. Instead, in this study we explored emotional state as an alternative access pathway to communication. We developed a pediatric BCI to identify positive and negative emotional states from changes in hemodynamic activity of the prefrontal cortex (PFC). To train and test the BCI, 10 neurotypical children aged 8–14 underwent a series of emotion-induction trials over four experimental sessions (one offline, three online) while their brain activity was measured with functional near-infrared spectroscopy (fNIRS). Visual neurofeedback was used to assist participants in regulating their emotional states and modulating their hemodynamic activity in response to the affective stimuli. Child-specific linear discriminant classifiers were trained on cumulatively available data from previous sessions and adaptively updated throughout each session. Average online valence classification exceeded chance across participants by the last two online sessions (with 7 and 8 of the 10 participants performing better than chance, respectively, in Sessions 3 and 4). There was a small significant positive correlation with online BCI performance and age, suggesting older participants were more successful at regulating their emotional state and/or brain activity. Variability was seen across participants in regards to BCI performance, hemodynamic response, and discriminatory features and channels. Retrospective offline analyses yielded accuracies comparable to those reported in adult affective BCI studies using fNIRS. Affective fNIRS-BCIs appear to be feasible for school-aged children, but to further gauge the practical potential of this type of BCI, replication with more training sessions, larger sample sizes, and end-users with disabilities is necessary.

Temel Duygusal Durumların Hemodinamik Karşılıklarının Taşınabilir bir İşlevsel Yakın Kızılaltı Spektroskopi Sistemi ile Tanımlanması

Objective: The aim of this study was to test the feasibility of a functional near infrared spectroscopy (fNIRS) system for quantification of the similarities and differences in the spatial localization of cerebral hemodynamic activation induced by visual presentation of neutral, negative and positive valence emotional stimuli. Method: 13 healthy subjects viewed neutral, pleasant and unpleasant pictures from the International Affective Picture System (IAPS) database in a block design experiment while the prefrontal cortical hemodynamic changes induced by emotional stimuli were continuously recorded with a 20 channel fNIRS system that covered the forehead region. Results: Negative valence pictures induced higher hemodynamic activity in right lateralized regions involving dorsolateral and oribtofrontal cortex when compared to neutral and positive valence stimuli (pFDR

Does active sitting provide more physiological changes than traditional sitting and standing workstations?

This cross-sectional study examined the physiological effects of two active chairs (AC1: had the feature to pedal and slide forward; AC2: was a multiaxial chair) compared to a traditional office chair and standing workstation. Twenty-four healthy participants computed at each of the workstations for 60 min. The active protocol was to alternate between a pedalling/side-to-side motion and sliding forward/front-to-back motion to the sound of a metronome operating at 40 bpm. The participants' physiological effects were recorded using near-infrared spectroscopy (NIRS); electrodermal activity (EDA) and a heart rate (HR) monitor for each collection period. Statistical analysis was conducted using a repeated measures analysis of variance for within-task and between-workstation comparisons. A Tukey's post hoc analysis was calculated for significant findings. Both active chairs significantly increased oxygenated blood in the gastrocnemius and participants' heart rate and EDA (stress) levels were affected slightly by task and time. However, participants felt more "productive" sitting in the control chair than in either of the active chairs.

A neural signature for combined action observation and motor imagery? An fNIRS study into prefrontal activation, automatic imitation, and self-other perceptions

INTRODUCTION

Research indicates that both observed and imagined actions can be represented in the brain as two parallel sensorimotor representations. One proposal is that higher order cognitive processes would align these two hypothetical action simulations.

METHODS

We investigated this hypothesis using an automatic imitation paradigm, with functional near-infrared spectroscopy recordings over the prefrontal cortex during different motor simulation states. On each trial, participants (n = 14) observed a picture of a rhythmical action (instructed action) followed by a distractor movie showing the same or different action. Participants then executed the instructed action. Distractor actions were manipulated to be fast or slow, and instructions were manipulated during distractor presentation: action observation (AO), combined action observation and motor imagery (AO+MI) and observe to imitate (intentional imitation). A pure motor imagery (MI) condition was also included.

RESULTS

Kinematic analyses showed that although distractor speed effects were significant under all instructions (shorter mean cycle times in execution for fast compared to slow trials), this imitation bias was significantly stronger for combined AO+MI than both AO and MI, and stronger for intentional imitation than the other three automatic imitation conditions. In the left prefrontal cortex, cerebral oxygenation was significantly greater for combined AO+MI than all other instructions. Participants reported that their representation of the self overlapped with the observed model significantly more during AO+MI than AO.

CONCLUSION

Left prefrontal activation may therefore be a neural signature of AO+MI, supporting attentional switching between concurrent representations of self (MI, top-down) and other (AO, bottom-up) to increase imitation and perceived closeness.

A systematic review of studies that used NIRS to measure neural activation during emotion processing in healthy individuals

Functional neuroimaging provides an avenue for earlier diagnosis and tailored treatment of psychological disorders characterised by emotional impairment. Near-infrared spectroscopy (NIRS) offers ecological advantages compared to other neuroimaging techniques and suitability of measuring regions involved in emotion functions. A systematic review was conducted to evaluate the capacity of NIRS to detect activation during emotion processing and to provide recommendations for future research. Following a comprehensive literature search, we reviewed 85 journal articles, which compared activation during emotional experience, regulation or perception with either a neutral condition or baseline period among healthy participants. The quantitative synthesis of outcomes was limited to thematical analysis, owing to the lack of standardisation between studies. Although most studies found increased prefrontal activity during emotional experience and regulation, the findings were more inconsistent for emotion perception. Some researchers reported increased activity during the task, some reported decreases, some no significant changes, and some reported mixed findings depending on the valence and region. We propose that variations in the cognitive task and stimuli, recruited sample, and measurement and analysis of data are the primary causes of inconsistency. Recommendations to improve consistency in future research by carefully considering the choice of population, cognitive task and analysis approach are provided.

Gratitude Affects Inter-Subjective Synchronicity for Cognitive Performance and Autonomic Responsiveness

Recently, social neurosciences have been interested in the investigation of neurophysiological responses related to the experience of positive emotions, such as gratitude, during social interactions. Specifically, the aim of the present research was to investigate whether gratitude related to gift exchange could favor cooperative behavior and bond construction, by improving behavioral and autonomic responsivity. At this regard, the autonomic synchronization and behavioral performance of 16 friends coupled in dyads were recorded during a joint attentional task. Gift exchange could be occurred either at the beginning or in the middle of the task. For the recording of simultaneous autonomic activity [heart rate (HR) and skin conductance level (SCL)], a hyperscanning biofeedback paradigm was used. Intra-subjective analysis showed an increase in behavioral [accuracy (ACC)] and autonomic responses (HR and SCL) when the gift exchange took place at the beginning of the task rather than in the middle. Moreover, inter-subjective analysis revealed an increase in behavioral performance and greater autonomic synchronization of HR index. The present research, therefore, shows how gratitude and trust experienced following gift exchange can modify participants’ reactions by creating a shared cognition and the adoption of joint strategies.

Prefrontal activation while listening to a letter of gratitude read aloud by a coworker face-to-face: A NIRS study

Near-infrared spectroscopy (NIRS) is a non-invasive functional brain imaging technique. NIRS is suitable for monitoring brain activation during social interactions. One of the omnipresent social interactions for employees is saying thank you and being thanked. It has been demonstrated that expressing and receiving gratitude leads to employees’ well-being and performance. To date, there have been no neuroimaging studies that monitor brain activity when receiving gratitude. Thus, we designed an experiment using NIRS to monitor brain function while listening to a letter of gratitude read by a coworker. We hypothesized that listening to a letter of gratitude read aloud by a co-worker in a face-to-face setting would have different effects on PFC activity than listening to a conversation about a neutral topic. We recruited 10 pairs of healthy right-handed employees. They were asked to write a letter of gratitude to their partner 1 week before the experiment. In the experiment, each pair sat face-to-face and read their letters aloud to each other. We evaluated changes in mood state before and after the experiment. NIRS was measured in each participant while they listened to their peers in the experimental condition (gratitude letter) and control condition (talking about the weather and date). The results suggested that negative mood state decreased after the experiment. Moreover, there were interaction effects between conditions and periods. Although further studies are needed to confirm the interpretation, our findings suggested that experience of being thanked was accompanied by prefrontal cortex activation.

The utility of NIRS technology for exploring emotional processing in children

BACKGROUND

Deficits in emotional processing and, in particular, in emotional self-regulation represent non-specific risk factors for transdiagnostic poor outcomes. Researches have been focusing on the investigation of possible emotional processing and regulation biomarkers. The present brief review of the literature aims to evaluate whether NIRS signal might be one of them.

METHODS

We reviewed 8 original articles investigating children's hemodynamic response to emotional tasks using NIRS, or exploring the association between NIRS response to cognitive tasks and behavioral emotional regulation.

RESULTS

All the works revised found significant associations between NIRS data and emotional indexes. Furthermore, significant hemodynamic response is found in different age-groups (3-12 years of age), suggesting that cortical response to emotional processing as measured by NIRS is a marker consistently recognizable throughout the development.

LIMITATIONS

Given that the studies in this field were still limited and used heterogeneous protocols, addressed different functions or aspects of emotional processing, these results are preliminary.

CONCLUSIONS

NIRS seems a reliable tool to describe brain activation during emotional processing and regulation. Moreover, it seems to be particularly useful in studies including either developmental-aged participants or clinical samples, due to its clear advantages and non-intrusiveness, offering a potential marker for deficits in emotional processing and regulation.

Random Subspace Ensemble Learning for Functional Near-Infrared Spectroscopy Brain-Computer Interfaces

The feasibility of the random subspace ensemble learning method was explored to improve the performance of functional near-infrared spectroscopy-based brain-computer interfaces (fNIRS-BCIs). Feature vectors have been constructed using the temporal characteristics of concentration changes in fNIRS chromophores such as mean, slope, and variance to implement fNIRS-BCIs systems. The mean and slope, which are the most popular features in fNIRS-BCIs, were adopted. Linear support vector machine and linear discriminant analysis were employed, respectively, as a single strong learner and multiple weak learners. All features in every channel and available time window were employed to train the strong learner, and the feature subsets were selected at random to train multiple weak learners. It was determined that random subspace ensemble learning is beneficial to enhance the performance of fNIRS-BCIs.

Cognitive and neural underpinnings of goal maintenance in young children

Active maintenance of goal representations is an integral part of our mental regulatory processes. Previous developmental studies have highlighted goal neglect, which is the phenomenon caused by a failure to maintain goal representations, and demonstrated developmental changes of the ability to maintain goal representations among preschoolers. Yet, few studies have explored the cognitive mechanisms underlying preschoolers' development of goal maintenance. The first aim of this study was to test whether working memory capacity and inhibitory control contribute to goal maintenance using a paradigm for measuring goal neglect. Moreover, although recent studies have shown that preschoolers recruit lateral prefrontal regions in performing executive functions tasks, they could not specify the neural underpinnings of goal maintenance. Thus, the second aim was to examine whether lateral prefrontal regions played a key role in maintaining goal representations using functional near-infrared spectroscopy. Our results showed that developmental differences in inhibitory control predicted the degree of goal neglect. It was also demonstrated that activation in the right prefrontal region was associated with children's successful avoidance of goal neglect. These findings offer important insights into the cognitive and neural underpinnings of goal maintenance in preschoolers.

The prefrontal cortex conscious and unconscious response to social/emotional facial expressions involve sex, hemispheric laterality, and selective activation of the central cardiac modulation

The human prefrontal cortex (PFC) processes complex sensory information for the elaboration of social behaviors. The non-invasive neuroimaging technique near-infrared spectroscopy (NIRS) identifies hemodynamic changes and concentration of oxygenated (HbO₂) and deoxygenated (HHb) hemoglobin in the cerebral cortex. We studied the responses detected by NIRS in the right and left PFC activation of 28 participants (n = 14 adult young females and males) while processing social/emotional facial expressions, i.e., in conscious perception of different expressions (neutral, happy, sad, angry, disgust, and fearful) and in unconscious/masked perception of negative expressions (fearful and disgust overlapped by neutral). The power spectral analysis from concomitant ECG signals revealed the sympathetic and parasympathetic modulation of cardiac responses. We found higher HbO₂ values in the right PFC of females than in males during, and in the left PFC after, following the conscious perception of the happy face. In males, the left PFC increased and the right PFC decreased HbO₂ while viewing the happy expression. In both sexes, HHb values were higher during the masked presentation of disgust than fearful expression, and after the masked presentation of fearful expression than during it. Higher sympathetic and lower parasympathetic activity (LF/ HF components) occurred in females when consciously and unconsciously processing negative emotions (p < 0.05 in all cases). These results demonstrate that the human PFC displays a selective activation depending on sex, hemispheric laterality, attention, time for responding to conscious and unconscious emotionally loaded stimuli with simulataneous centrally modulated cardiovascular responses.

Human Discrimination and Categorization of Emotions in Voices: A Functional Near-Infrared Spectroscopy (fNIRS) Study

Functional Near-Infrared spectroscopy (fNIRS) is a neuroimaging tool that has been recently used in a variety of cognitive paradigms. Yet, it remains unclear whether fNIRS is suitable to study complex cognitive processes such as categorization or discrimination. Previously, functional imaging has suggested a role of both inferior frontal cortices in attentive decoding and cognitive evaluation of emotional cues in human vocalizations. Here, we extended paradigms used in functional magnetic resonance imaging (fMRI) to investigate the suitability of fNIRS to study frontal lateralization of human emotion vocalization processing during explicit and implicit categorization and discrimination using mini-blocks and event-related stimuli. Participants heard speech-like but semantically meaningless pseudowords spoken in various tones and evaluated them based on their emotional or linguistic content. Behaviorally, participants were faster to discriminate than to categorize; and processed the linguistic faster than the emotional content of stimuli. Interactions between condition (emotion/word), task (discrimination/categorization) and emotion content (anger, fear, neutral) influenced accuracy and reaction time. At the brain level, we found a modulation of the Oxy-Hb changes in IFG depending on condition, task, emotion and hemisphere (right or left), highlighting the involvement of the right hemisphere to process fear stimuli, and of both hemispheres to treat anger stimuli. Our results show that fNIRS is suitable to study vocal emotion evaluation, fostering its application to complex cognitive paradigms.

Uncovering electrophysiological and vascular signatures of implicit emotional prosody

The capability of differentiating between various emotional states in speech displays a crucial prerequisite for successful social interactions. The aim of the present study was to investigate neural processes underlying this differentiating ability by applying a simultaneous neuroscientific approach in order to gain both electrophysiological (via electroencephalography, EEG) and vascular (via functional near-infrared-spectroscopy, fNIRS) responses. Pseudowords conforming to angry, happy, and neutral prosody were presented acoustically to participants using a passive listening paradigm in order to capture implicit mechanisms of emotional prosody processing. Event-related brain potentials (ERPs) revealed a larger P200 and an increased late positive potential (LPP) for happy prosody as well as larger negativities for angry and neutral prosody compared to happy prosody around 500 ms. FNIRS results showed increased activations for angry prosody at right fronto-temporal areas. Correlation between negativity in the EEG and activation in fNIRS for angry prosody suggests analogous underlying processes resembling a negativity bias. Overall, results indicate that mechanisms of emotional and phonological encoding (P200), emotional evaluation (increased negativities) as well as emotional arousal and relevance (LPP) are present during implicit processing of emotional prosody.

Hemodynamic responses in prefrontal cortex and personality characteristics in patients with bulimic disorders: a near-infrared spectroscopy study

PURPOSE

This study sought to identify the prefrontal cortex hemodynamic response that is dependent on cognitive performance in patients with bulimic disorders (BD), and investigate its association with personality characteristics.

METHODS

Nineteen female patients with BD and 23 healthy women were recruited. Their personality characteristics related to eating disorders were examined using a self-reporting questionnaire, namely the eating disorder inventory-2 (EDI-2). Cerebral blood flow response in the prefrontal cortex during the digit span backward task (DSBT) was measured using near-infrared spectroscopy (NIRS). Change in oxygenated hemoglobin concentration (ΔoxyHb), obtained using NIRS, were used as an index of brain activity. Further, the relationship between prefrontal cortical activity and personality characteristics was investigated in patients with BD.

RESULTS

The cognitive performance of patients with BD was significantly lower in the DSBT compared with healthy subjects. There was no difference between the groups in ΔoxyHb during the task. Task scores of patients with BD correlated with asceticism and perfectionism. Moreover, the asceticism score was negatively correlated with ΔoxyHb of the bilateral prefrontal cortex in patients with BD.

CONCLUSION

The results suggest that cognitive performance and brain activity induced during DSBT might be affected by asceticism in BD patients.

LEVEL OF EVIDENCE

III, case-control study.

Open-Access fNIRS Dataset for Classification of Unilateral Finger- and Foot-Tapping

Numerous open-access electroencephalography (EEG) datasets have been released and widely employed by EEG researchers. However, not many functional near-infrared spectroscopy (fNIRS) datasets are publicly available. More fNIRS datasets need to be freely accessible in order to facilitate fNIRS studies. Toward this end, we introduce an open-access fNIRS dataset for three-class classification. The concentration changes of oxygenated and reduced hemoglobin were measured, while 30 volunteers repeated each of the three types of overt movements (i.e., left- and right-hand unilateral complex finger-tapping, foot-tapping) for 25 times. The ternary support vector machine (SVM) classification accuracy obtained using leave-one-out cross-validation was estimated at 70.4% ± 18.4% on average. A total of 21 out of 30 volunteers scored a superior binary SVM classification accuracy (left-hand vs. right-hand finger-tapping) of over 80.0%. We believe that the introduced fNIRS dataset can facilitate future fNIRS studies.

Prefrontal cortex activity triggered by affective faces exposure and its relationship with neuroticism

The emotional processing of affective faces is an essential element of social relationships. Individual differences in personality traits such as neuroticism can influence how we manage these interactions. The objective of this study was to analyze changes in prefrontal cortex (PFC) activity in response to visual exposure to affective faces, and to ascertain whether changes in PFC activity were related to scores in neuroticism, including depression, anxiety, low self-esteem and dependence facets. Fifty-two healthy undergraduate female students participated in the present study. Results showed significant differences depending on face valence in the left and right ventrolateral PFC. We found a reduction in oxygen consumption in reaction to neutral and happy faces, and a small increase in oxygenation in reaction to angry faces both in the left and the right PFC. There were significant positive correlations in the left ventrolateral PFC between oxygenation changes during exposure to neutral and happy faces and the neuroticism factor. Anxiety and depression facets showed positive significant correlations with oxygenation changes for all Time blocks. Notice that participants with high neuroticism scores did not show differences in ventrolateral PFC activity depending on face valence. We suggest that PFC would play a protective role in response to emotional stimuli. The reduced regulatory control of PFC over the amygdala could explain vulnerability to emotional disorders in subjects with high neuroticism.

Endurance Exercise Enhances Emotional Valence and Emotion Regulation

Acute exercise consistently benefits both emotion and cognition, particularly cognitive control. We evaluated acute endurance exercise influences on emotion, domain-general cognitive control and the cognitive control of emotion, specifically cognitive reappraisal. Thirty-six endurance runners, defined as running at least 30 miles per week with one weekly run of at least 9 miles (21 female, age 18-30 years) participated. In a repeated measures design, participants walked at 57% age-adjusted maximum heart rate (HRmax; range 51%-63%) and ran at 70% HRmax (range 64%-76%) for 90 min on two separate days. Participants completed measures of emotional state and the Stroop test of domain-general cognitive control before, every 30 min during and 30 min after exercise. Participants also completed a cognitive reappraisal task (CRT) after exercise. Functional near-infrared spectroscopy (fNIRS) tracked changes in oxygenated and deoxygenated hemoglobin (O2Hb and dHb) levels in the prefrontal cortex (PFC). Results suggest that even at relatively moderate intensities, endurance athletes benefit emotionally from running both during and after exercise and task-related PFC oxygenation reductions do not appear to hinder prefrontal-dependent cognitive control.

Prefrontal oxygenation correlates to the responses in facial skin blood flows during exposure to pleasantly charged movie

Our laboratory reported that facial skin blood flow may serve as a sensitive tool to assess an emotional status. Cerebral neural correlates during emotional interventions should be sought in relation to the changes in facial skin blood flow. To test the hypothesis that prefrontal activity has positive relation to the changes in facial skin blood flow during emotionally charged stimulation, we examined the dynamic changes in prefrontal oxygenation (with near‐infrared spectroscopy) and facial skin blood flows (with two‐dimensional laser speckle and Doppler flowmetry) during emotionally charged audiovisual challenges for 2 min (by viewing comedy, landscape, and horror movie) in 14 subjects. Hand skin blood flow and systemic hemodynamics were simultaneously measured. The extents of pleasantness and consciousness for each emotional stimulus were estimated by subjective rating from −5 (the most unpleasant; the most unconscious) to +5 (the most pleasant; the most conscious). Positively charged emotional stimulation (comedy) simultaneously decreased (P < 0.05) prefrontal oxygenation and facial skin blood flow, whereas negatively charged (horror) or neutral (landscape) emotional stimulation did not alter or slightly decreased them. Any of hand skin blood flow and systemic cardiovascular variables did not change significantly during positively charged emotional stimulation. The changes in prefrontal oxygenation had a highly positive correlation with the changes in facial skin blood flow without altering perfusion pressure, and they were inversely correlated with the subjective rating of pleasantness. The reduction in prefrontal oxygenation during positively charged emotional stimulation suggests a decrease in prefrontal neural activity, which may in turn elicit neurally mediated vasoconstriction of facial skin blood vessels.

Emotional Processing in the First 2 Years of Life: A Review of Near-Infrared Spectroscopy Studies

Emotional stimuli processing during childhood helps us to detect salient cues in our environment and prepares us for our social life. In early childhood, the emotional valences of auditory and visual input are salient and relevant cues of social aspects of the environment, and it is of special interest to understand how exactly the processing of emotional stimuli develops. Near‐infrared spectroscopy (NIRS) is a noninvasive neuroimaging tool that has proven valuable in studying emotional processing in children. After conducting a systematic search of PubMed, Web of Science, and Embase databases, we examined 50 NIRS studies performed to study emotional stimuli processing in children in the first 2 years of age. We found that the majority of these studies are done in infants and the most commonly used stimuli are visual and auditory. Many of the reviewed studies suggest the involvement of bilateral temporal areas in emotional processing of visual and auditory stimuli. It is unclear which neural activation patterns reflect maturation and at what age the emotional encoding reaches those typically seen in adults. Our review provides an overview of the database on emotional processing in children up to 2 years of age. Furthermore, it demonstrates the need to include the less‐studied age range of 1 to 2 years, and suggests the use of combined audio‐visual stimuli and longitudinal studies for future research on emotional processing in children. Thus, NIRS might be a vital tool to study the associations between the early pattern of neural responses and socioemotional development later in life.

Eyes-closed hybrid brain-computer interface employing frontal brain activation

Brain-computer interfaces (BCIs) have been studied extensively in order to establish a non-muscular communication channel mainly for patients with impaired motor functions. However, many limitations remain for BCIs in clinical use. In this study, we propose a hybrid BCI that is based on only frontal brain areas and can be operated in an eyes-closed state for end users with impaired motor and declining visual functions. In our experiment, electroencephalography (EEG) and near-infrared spectroscopy (NIRS) were simultaneously measured while 12 participants performed mental arithmetic (MA) and remained relaxed (baseline state: BL). To evaluate the feasibility of the hybrid BCI, we classified MA- from BL-related brain activation. We then compared classification accuracies using two unimodal BCIs (EEG and NIRS) and the hybrid BCI in an offline mode. The classification accuracy of the hybrid BCI (83.9 ± 10.3%) was shown to be significantly higher than those of unimodal EEG-based (77.3 ± 15.9%) and NIRS-based BCI (75.9 ± 6.3%). The analytical results confirmed performance improvement with the hybrid BCI, particularly for only frontal brain areas. Our study shows that an eyes-closed hybrid BCI approach based on frontal areas could be applied to neurodegenerative patients who lost their motor functions, including oculomotor functions.

Predicting affective valence using cortical hemodynamic signals

Ascribing affective valence to stimuli or mental states is a fundamental property of human experiences. Recent neuroimaging meta-analyses favor the workspace hypothesis for the neural underpinning of valence, in which both positive and negative values are encoded by overlapping networks but are associated with different patterns of activity. In the present study, we further explored this framework using functional near-infrared spectroscopy (fNIRS) in conjunction with multivariate analyses. We monitored the fronto-temporal and occipital hemodynamic activity of 49 participants during the viewing of affective images (passive condition) and during the imagination of affectively loaded states (active condition). Multivariate decoding techniques were applied to determine whether affective valence is encoded in the cortical areas assessed. Prediction accuracies of 89.90 ± 13.84% and 85.41 ± 14.43% were observed for positive versus neutral comparisons, and of 91.53 ± 13.04% and 81.54 ± 16.05% for negative versus neutral comparisons (passive/active conditions, respectively). Our results are consistent with previous studies using other neuroimaging modalities that support the affective workspace hypothesis and the notion that valence is instantiated by the same network, regardless of whether the affective experience is passively or actively elicited.

Test-retest reliability of the prefrontal response to affective pictures based on functional near-infrared spectroscopy

Functional near-infrared spectroscopy (fNIRS) is being increasingly applied to affective and social neuroscience research; however, the reliability of this method is still unclear. This study aimed to evaluate the test–retest reliability of the fNIRS-based prefrontal response to emotional stimuli. Twenty-six participants viewed unpleasant and neutral pictures, and were simultaneously scanned by fNIRS in two sessions three weeks apart. The reproducibility of the prefrontal activation map was evaluated at three spatial scales (mapwise, clusterwise, and channelwise) at both the group and individual levels. The influence of the time interval was also explored and comparisons were made between longer (intersession) and shorter (intrasession) time intervals. The reliabilities of the activation map at the group level for the mapwise (up to 0.88, the highest value appeared in the intersession assessment) and clusterwise scales (up to 0.91, the highest appeared in the intrasession assessment) were acceptable, indicating that fNIRS may be a reliable tool for emotion studies, especially for a group analysis and under larger spatial scales. However, it should be noted that the individual-level and the channelwise fNIRS prefrontal responses were not sufficiently stable. Future studies should investigate which factors influence reliability, as well as the validity of fNIRS used in emotion studies.

A Brief Review of Research Using Near-Infrared Spectroscopy to Measure Activation of the Prefrontal Cortex during Emotional Processing: The Importance of Experimental Design

During the past two decades there has been a pronounced increase in the number of published research studies that have employed near-infrared spectroscopy (NIRS) to measure neural activation. The technique is now an accepted neuroimaging tool adopted by cognitive neuroscientists to investigate a number of fields, one of which is the study of emotional processing. Crucially, one brain region that is important to the processing of emotional information is the prefrontal cortex (PFC) and NIRS is ideally suited to measuring activity in this region. Compared to other methods used to record neural activation, NIRS reduces the discomfort to participants, makes data collection from larger sample sizes more achievable, and allows measurement of activation during tasks involving physical movement. However, the use of NIRS to investigate the links between emotion and cognition has revealed mixed findings. For instance, whilst some studies report increased PFC activity associated with the processing of negative information, others show increased activity in relation to positive information. Research shows differences in PFC activity between different cognitive tasks, yet findings also vary within similar tasks. This work reviews a selection of recent studies that have adopted NIRS to study PFC activity during emotional processing in both healthy individuals and patient populations. It highlights the key differences between research findings and argues that variations in experimental design could be a contributing factor to the mixed results. Guidance is provided for future work in this area in order to improve consistency within this growing field.

Simultaneous recording of EEG and fNIRS during visuo-spatial and facial expression processing in a dual task paradigm

Emotional processing is probably the most crucial tool for orienting oneself in our everyday social life and has been considered to be highly automatic for a long time. Dual task (DT) research shows that information competing for working memory resources impairs the identification of emotional facial expressions. Effects of cognitive load in DT paradigms have been confirmed in numerous neuroimaging studies. However, interference occurring during a DT comprised of decoding emotional facial expressions and a visuo-spatial working memory task has yet to be visualized. To investigate the DT interference effect on brain areas associated not only with working memory, but also emotional and visuo-spatial processing, we recorded brain activation within the prefrontal cortex and parietal-occipital sensory areas using functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG) simultaneously. Our study consisted of N = 36 participants (27 female) performing the following tasks: a) Corsi blocks, b) identification of emotional facial expressions or c) DT comprising of tasks a) and b). We predicted higher activation of the prefrontal cortex during DT and corresponding reduced P100 and P300 amplitudes. As expected, fNIRS measurements revealed significantly higher neuronal activation within the prefrontal cortex in the DT condition. When comparing DT to the single tasks, the P100 amplitude was reduced, but the P300 amplitude did not show the expected reduction. Our findings underline that at least some aspects of emotional processing are not entirely automatic, but depend on prefrontal control and are therefore affected by cognitive load, in particular visuo-spatial working memory resources.

Brain tissue oxygen evaluation by wireless near-infrared spectroscopy

BACKGROUND

Monitoring the partial pressure of oxygen in brain tissue (PbtO2) is an important tool for traumatic brain injury (TBI) but is invasive and inconvenient for real time monitoring. Near-infrared spectroscopy (NIRS), which can monitor hemoglobin parameters in the brain tissue, has been used widely as a noninvasive tool for assessing cerebral ischemia and hypoxia. Therefore, it may have the potential as a noninvasive tool for estimating the change of PbtO2. In this study, a novel wireless NIRS system was designed to monitor hemoglobin parameters of rat brains under different impact strengths and was used to estimate the change of PbtO2 noninvasively in TBI.

MATERIALS AND METHODS

The proposed wireless NIRS system and a PbtO2 monitoring system were used to monitor the oxygenation of rat brains under different impact strengths. Rats were randomly assigned to four different impact strength groups (sham, 1.6 atm, 2.0 atm, and 2.4 atm; n = 6 per group), and the relationships of concentration changes in oxyhemoglobin (HbO2), deoxyhemoglobin (HbR), and total hemoglobin (HbT), and PbtO2 during and after TBI with different impact strengths were investigated. Triphenyltetrazolium chloride (TTC) staining was also used to evaluate infarction volume.

RESULTS

Concentration changes in HbO2, HbR, and HbT dropped immediately after the impact, increased gradually, and then became stable. Changes in PbtO2 had a similar tendency with the hemoglobin parameters. There was significant correlation between changes in PbtO2 and HbO2 (correlation = 0.76) but not with changes in HbR (correlation = 0.06). In triphenyltetrazolium chloride staining, the infarction volume was highly but negatively associated with oxygen-related parameters like PbtO2 and HbO2.

CONCLUSIONS

Changes in HbO2 under TBI was highly and positively correlated with changes in PbtO2. By using the relative changes in HbO2 as a reference parameter, the proposed wireless NIRS system may be developed as a noninvasive tool for estimating the change of PbtO2 in brain tissue after TBI.

Post-operative benefits of animal-assisted therapy in pediatric surgery: a randomised study

Background

Interest in animal-assisted therapy has been fuelled by studies supporting the many health benefits. The purpose of this study was to better understand the impact of an animal-assisted therapy program on children response to stress and pain in the immediate post-surgical period.

Patients and Methods

Forty children (3–17 years) were enrolled in the randomised open-label, controlled, pilot study. Patients were randomly assigned to the animal-assisted therapy-group (n = 20, who underwent a 20 min session with an animal-assisted therapy dog, after surgery) or the standard-group (n = 20, standard postoperative care). The study variables were determined in each patient, independently of the assigned group, by a researcher unblinded to the patient’s group. The outcomes of the study were to define the neurological, cardiovascular and endocrinological impact of animal-assisted therapy in response to stress and pain. Electroencephalogram activity, heart rate, blood pressure, oxygen saturation, cerebral prefrontal oxygenation, salivary cortisol levels and the faces pain scale were considered as outcome measures.

Results

After entrance of the dog faster electroencephalogram diffuse beta-activity (> 14 Hz) was reported in all children of the animal-assisted therapy group; in the standard-group no beta-activity was recorded (100% vs 0%, p<0.001). During observation, some differences in the time profile between groups were observed for heart rate (test for interaction p = 0.018), oxygen saturation (test for interaction p = 0.06) and cerebral oxygenation (test for interaction p = 0.09). Systolic and diastolic blood pressure were influenced by animal-assisted therapy, though a higher variability in diastolic pressure was observed. Salivary cortisol levels did not show different behaviours over time between groups (p=0.70). Lower pain perception was noted in the animal-assisted group in comparison with the standard-group (p = 0.01).

Conclusion

Animal-assisted therapy facilitated rapid recovery in vigilance and activity after anaesthesia, modified pain perception and induced emotional prefrontal responses. An adaptative cardiovascular response was also present.

Trial Registration

ClinicalTrials.gov NCT02284100

Association of autism tendency and hemodynamic changes in the prefrontal cortex during facial expression stimuli measured by multi-channel near-infrared spectroscopy

AIM

The aim of this study is to examine the hemodynamic changes induced by the cognitive process of facial expression by using multi-channel near-infrared spectroscopy in healthy subjects with varying degrees of autism tendency.

METHODS

Subjects were 38 volunteers, 20 men and 18 women. Autism tendency was measured by the Autism Spectrum Quotient. The hemodynamic changes in the prefrontal cortex were measured by 24-channel near-infrared spectroscopy system, while subjects were asked to judge their own emotional response to standardized pictures of eight kinds of facial expressions on a computer screen.

RESULTS

There were significant negative correlations between Autism Spectrum Quotient scores and accuracy of fearful expression recognition as well as increases in the concentration of oxygenated hemoglobin in response to four kinds of emotional faces (fear, contempt, sadness and disgust).

CONCLUSION

Our findings suggest that the greater tendency to autism that subjects have, the more difficulty they have in recognizing a fearful expression and the less hemodynamic change in the prefrontal cortex they show in response to negative facial expressions.

What hemodynamic (fNIRS), electrophysiological (EEG) and autonomic integrated measures can tell us about emotional processing

Due to its fast temporal evolution and its representation and integration among complex and widespread neural networks, the emotion perception process should preferably be examined by means of multimethodological approach. Indeed the indubitable vantage of acquiring both the autonomic (arousal-related) and the central (cortical-related) activities stands in the possibility to better elucidate the reciprocal interplay of the two compartments. In the present study EEG (frequency band analysis), systemic SCR and heart rate (HR) were all recorded simultaneously with hemodynamic (NIRS, Near-Infrared Spectroscopy) measurements as potential biological markers of emotions, related to both central and peripheral systems. These multiple measures were then related to the self-report correlates, that is the subjective appraisal in term of valence (positive vs. negative) and arousal (high vs. low) by using SAM rating. Twenty subjects were submitted to emotional cues processing (IAPS) when fNIRS, frequency bands (alpha, beta, delta, theta), SCR and HR were recorded. As shown by O2Hb increasing within the right hemisphere, the contribution of prefrontal cortex was elucidated, by pointing out a relevant lateralization effect (more right-PFC activity) induced by the specific valence (negative) of the emotional patterns. Secondly, EEG activity (mainly low-frequency theta and delta bands) was intrinsically associated with the cortical hemodynamic responsiveness to the negative emotional patterns, within the right side. Finally SCR increased mainly in response to negative patterns, and the autonomic behavior was related to explicit (SAM) and cortical (NIRS; EEG) activity. The intrinsic relationships between these three different levels are discussed.

Influence of subjective happiness on the prefrontal brain activity: an fNIRS study

Focusing on the relationship between subjective happiness (SH) and emotional changes, we examined influences of SH on emotion-related prefrontal activity using multichannel NIRS. The International Affective Picture System (IAPS) was used to evoke emotional changes. Subjects were a total of 18 right-handed healthy students. Frequency of picture-induced increases in oxygenated haemoglobin (oxy-Hb) was evaluated. Subjects with a high SH score had a higher frequency of increased oxy-Hb in the left prefrontal cortex (PFC) while viewing pleasant pictures, whereas they showed a lower frequency in the right PFC while viewing unpleasant pictures. It is well known that the left PFC and right PFC are engaged in different ways in the emotional processes. Although further investigations are required, the present results indicate that the SH level influences the right-left differences in emotion-related prefrontal activity.

Activation of the rostromedial prefrontal cortex during the experience of positive emotion in the context of esthetic experience. An fNIRS study

The contemplation of visual art requires attention to be directed to external stimulus properties and internally generated thoughts. It has been proposed that the medial rostral prefrontal cortex (rPFC; BA10) plays a role in the maintenance of attention on external stimuli whereas the lateral area of the rPFC is associated with the preservation of attention on internal cognitions. An alternative hypothesis associates activation of medial rPFC with internal cognitions related to the self during emotion regulation. The aim of the current study was to differentiate activation within rPFC using functional near infrared spectroscopy (fNIRS) during the viewing of visual art selected to induce positive and negative valence, which were viewed under two conditions: (1) emotional introspection and (2) external object identification. Thirty participants (15 female) were recruited. Sixteen pre-rated images that represented either positive or negative valence were selected from an existing database of visual art. In one condition, participants were directed to engage in emotional introspection during picture viewing. The second condition involved a spot-the-difference task where participants compared two almost identical images, a viewing strategy that directed attention to external properties of the stimuli. The analysis revealed a significant increase of oxygenated blood in the medial rPFC during viewing of positive images compared to negative images. This finding suggests that the rPFC is involved during positive evaluations of visual art that may be related to judgment of pleasantness or attraction. The fNIRS data revealed no significant main effect between the two viewing conditions, which seemed to indicate that the emotional impact of the stimuli remained unaffected by the two viewing conditions.

NIRS as a tool for assaying emotional function in the prefrontal cortex

Despite having relatively poor spatial and temporal resolution, near-infrared spectroscopy (NIRS) has several methodological advantages compared with other non-invasive measurements of neural activation. For instance, the unique characteristics of NIRS give it potential as a tool for investigating the role of the prefrontal cortex (PFC) in emotion processing. However, there are several obstacles in the application of NIRS to emotion research. In this mini-review, we discuss the findings of studies that used NIRS to assess the effects of PFC activation on emotion. Specifically, we address the methodological challenges of NIRS measurement with respect to the field of emotion research, and consider potential strategies for mitigating these problems. In addition, we show that two fields of research, investigating (i) biological predisposition influencing PFC responses to emotional stimuli and (ii) neural mechanisms underlying the bi-directional interaction between emotion and action, have much to gain from the use of NIRS. With the present article, we aim to lay the foundation for the application of NIRS to the above-mentioned fields of emotion research.

Show me how you walk and I tell you how you feel - a functional near-infrared spectroscopy study on emotion perception based on human gait

The ability to recognize and adequately interpret emotional states in others plays a fundamental role in regulating social interaction. Body language presents an essential element of nonverbal communication which is often perceived prior to mimic expression. However, the neural networks that underlie the processing of emotionally expressive body movement and body posture are poorly understood. 33 healthy subjects have been investigated using the optically based imaging method functional near-infrared spectroscopy (fNIRS) during the performance of a newly developed emotion discrimination paradigm consisting of faceless avatars expressing fearful, angry, sad, happy or neutral gait patterns. Participants were instructed to judge (a) the presented emotional state (emotion task) and (b) the observed walking speed of the respective avatar (speed task). We measured increases in cortical oxygenated haemoglobin (O2HB) in response to visual stimulation during emotion discrimination. These O2HB concentration changes were enhanced for negative emotions in contrast to neutral gait sequences in right occipito-temporal and left temporal and temporo-parietal brain regions. Moreover, fearful and angry bodies elicited higher activation increases during the emotion task compared to the speed task. Haemodynamic responses were correlated with a number of behavioural measures, whereby a positive relationship between emotion regulation strategy preference and O2HB concentration increases after sad walks was mediated by the ability to accurately categorize sad walks. Our results support the idea of a distributed brain network involved in the recognition of bodily emotion expression that comprises visual association areas as well as body/movement perception specific cortical regions that are also sensitive to emotion. This network is activated less when the emotion is not intentionally processed (i.e. during the speed task). Furthermore, activity of this perceptive network is, mediated by the ability to correctly recognize emotions, indirectly connected to active emotion regulation processes. We conclude that a full understanding of emotion perception and its neural substrate requires the investigation of dynamic representations and means of expression other than the face.

Passive heat exposure induced by hot water leg immersion increased oxyhemoglobin in pre-frontal cortex to preserve oxygenation and did not contribute to impaired cognitive functioning

This study investigated the effects of passive heat exposure on pre-frontal cortex oxygenation and cognitive functioning, specifically to examine whether the change in pre-frontal cortex oxygenation coincided with cognitive functioning during heat exposure. Eleven male students who participated in this study immersed their lower legs to the knees in three different water temperatures, 38 °C, 40 °C, and 42 °C water in an air temperature of 28 º C and 50 % relative humidity for 60 min. After 45 min of leg immersion they performed cognitive functioning tasks assessing their short-term memory while immersing their lower legs. There were higher rectal temperature (P < 0.05) and higher increase of oxyhemoglobin in both left (P < 0.05) and right (P < 0.05) pre-frontal cortex at the final stage of 45-min leg immersion in the 42 °C condition with unaltered tissue oxygenation index among the three conditions (P > 0.05). No statistical difference in cognitive functioning among the three conditions was observed with a higher increase of oxyhemoglobin during the cognitive functioning in the 42 °C condition for the left (P = 0.05) and right (P < 0.05) pre-frontal cortex. The findings of this study suggest, first, passive heat exposure increases oxygen delivery in the pre-frontal cortex to maintain pre-frontal cortex oxygenation; second, there is no evidence of passive heat exposure in cognitive functioning in this study; and third, the greater increases of oxyhemoglobin in the pre-frontal cortex during cognitive functioning at the hottest condition suggests a recruitment of available neural resources or greater effort to maintain the same performance at the same level as when they felt thermally comfortable.

Characterizing emotional response to music in the prefrontal cortex using near infrared spectroscopy

Known to be involved in emotional processing the human prefrontal cortex (PFC), can be non-invasively monitored using near-infrared spectroscopy (NIRS). As such, PFC NIRS can serve as a means for studying emotional processing by the PFC. Identifying patterns associated with emotions in PFC using NIRS may provide a means of bedside emotion identification for nonverbal children and youth with severe physical disabilities. In this study, NIRS was used to characterize the PFC hemodynamic response to emotional arousal and valence in a music-based emotion induction paradigm in 9 individuals without disabilities or known health conditions. In particular, a novel technique based on wavelet-based peak detection was used to characterize chromophore concentration patterns. The maximum wavelet coefficients extracted from oxygenated hemoglobin concentration waveforms from all nine recording locations on the PFC were significantly associated with emotional valence and arousal. Specifically, high arousal and negative emotions were associated with larger maximum wavelet coefficients.

Intersession consistency of single-trial classification of the prefrontal response to mental arithmetic and the no-control state by NIRS

Near-infrared spectroscopy (NIRS) has been recently investigated for use in noninvasive brain-computer interface (BCI) technologies. Previous studies have demonstrated the ability to classify patterns of neural activation associated with different mental tasks (e.g., mental arithmetic) using NIRS signals. Though these studies represent an important step towards the realization of an NIRS-BCI, there is a paucity of literature regarding the consistency of these responses, and the ability to classify them on a single-trial basis, over multiple sessions. This is important when moving out of an experimental context toward a practical system, where performance must be maintained over longer periods. When considering response consistency across sessions, two questions arise: 1) can the hemodynamic response to the activation task be distinguished from a baseline (or other task) condition, consistently across sessions, and if so, 2) are the spatiotemporal characteristics of the response which best distinguish it from the baseline (or other task) condition consistent across sessions. The answers will have implications for the viability of an NIRS-BCI system, and the design strategies (especially in terms of classifier training protocols) adopted. In this study, we investigated the consistency of classification of a mental arithmetic task and a no-control condition over five experimental sessions. Mixed model linear regression on intrasession classification accuracies indicate that the task and baseline states remain differentiable across multiple sessions, with no significant decrease in accuracy (p = 0.67). Intersession analysis, however, revealed inconsistencies in spatiotemporal response characteristics. Based on these results, we investigated several different practical classifier training protocols, including scenarios in which the training and test data come from 1) different sessions, 2) the same session, and 3) a combination of both. Results indicate that when selecting optimal classifier training protocols for NIRS-BCI, a compromise between accuracy and convenience (e.g., in terms of duration/frequency of training data collection) must be considered.

Medial prefrontal cortex activity during the extinction of conditioned fear: an investigation using functional near-infrared spectroscopy

The majority of fear conditioning studies in humans have focused on fear acquisition rather than fear extinction. For this reason only a few functional imaging studies on fear extinction are available. A large number of animal studies indicate the medial prefrontal cortex (mPFC) as neuronal substrate of extinction. We therefore determined mPFC contribution during extinction learning after a discriminative fear conditioning in 34 healthy human subjects by using functional near-infrared spectroscopy. During the extinction training, a previously conditioned neutral face (conditioned stimulus, CS+) no longer predicted an aversive scream (unconditioned stimulus, UCS). Considering differential valence and arousal ratings as well as skin conductance responses during the acquisition phase, we found a CS+ related increase in oxygenated haemoglobin concentration changes within the mPFC over the time course of extinction. Late CS+ trials further revealed higher activation than CS- trials in a cluster of probe set channels covering the mPFC. These results are in line with previous findings on extinction and further emphasize the mPFC as significant for associative learning processes. During extinction, the diminished fear association between a former CS+ and a UCS is inversely correlated with mPFC activity--a process presumably dysfunctional in anxiety disorders.

Automatic single-trial discrimination of mental arithmetic, mental singing and the no-control state from prefrontal activity: toward a three-state NIRS-BCI

Background

Near-infrared spectroscopy (NIRS) is an optical imaging technology that has recently been investigated for use in a safe, non-invasive brain-computer interface (BCI) for individuals with severe motor impairments. To date, most NIRS-BCI studies have attempted to discriminate two mental states (e.g., a mental task and rest), which could potentially lead to a two-choice BCI system. In this study, we attempted to automatically differentiate three mental states - specifically, intentional activity due to 1) a mental arithmetic (MA) task and 2) a mental singing (MS) task, and 3) an unconstrained, "no-control (NC)" state - to investigate the feasibility of a three-choice system-paced NIRS-BCI.

Results

Deploying a dual-wavelength frequency domain near-infrared spectrometer, we interrogated nine sites around the frontopolar locations while 7 able-bodied adults performed mental arithmetic and mental singing to answer multiple-choice questions within a system-paced paradigm. With a linear classifier trained on a ten-dimensional feature set, an overall classification accuracy of 56.2% was achieved for the MA vs. MS vs. NC classification problem and all individual participant accuracies significantly exceeded chance (i.e., 33%). However, as anticipated based on results of previous work, the three-class discrimination was unsuccessful for three participants due to the ineffectiveness of the mental singing task. Excluding these three participants increases the accuracy rate to 62.5%. Even without training, three of the remaining four participants achieved accuracies approaching 70%, the value often cited as being necessary for effective BCI communication.

Conclusions

These results are encouraging and demonstrate the potential of a three-state system-paced NIRS-BCI with two intentional control states corresponding to mental arithmetic and mental singing.