Separation of fNIRS signals into functional and systemic components based on differences in hemodynamic modalities

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.

Functional near-infrared-spectroscopy-based measurement of changes in cortical activity in macaques during post-infarct recovery of manual dexterity

Because compensatory changes in brain activity underlie functional recovery after brain damage, monitoring of these changes will help to improve rehabilitation effectiveness. Functional near-infrared spectroscopy (fNIRS) has the potential to measure brain activity in freely moving subjects. We recently established a macaque model of internal capsule infarcts and an fNIRS system for use in the monkey brain. Here, we used these systems to study motor recovery in two macaques, for which focal infarcts of different sizes were induced in the posterior limb of the internal capsule. Immediately after the injection, flaccid paralysis was observed in the hand contralateral to the injected hemisphere. Thereafter, dexterous hand movements gradually recovered over months. After movement recovery, task-evoked hemodynamic responses increased in the ventral premotor cortex (PMv). The response in the PMv of the infarcted (i.e., ipsilesional) hemisphere increased in the monkey that had received less damage. In contrast, the PMv of the non-infarcted (contralesional) hemisphere was recruited in the monkey with more damage. A pharmacological inactivation experiment with muscimol suggested the involvement of these areas in dexterous hand movements during recovery. These results indicate that fNIRS can be used to evaluate brain activity changes crucial for functional recovery after brain damage.

The Temporal Confounding Effects of Extra-cerebral Contamination Factors on the Hemodynamic Signal Measured by Functional Near-Infrared Spectroscopy

Introduction: Functional near-infrared spectroscopy (fNIRS) has been broadly applied for optical brain imaging. This method is hemodynamic-based functional brain imaging relying on the measurement of the neurovascular coupling to detect changes in cerebral neuronal activities. The extra-cerebral hemodynamic changes are important contaminating factors in fNIRS measurements. This error signal can be misinterpreted as cerebral activities during fNIRS studies. Recently, it was assumed that temporal changes in deoxygenated hemoglobin concentration [HHb] was hardly affected by superficial blood flow, and it was proposed that the activation maps could be determined from [HHb] at large source-detector separation. Methods: In the current study, we measured the temporal changes in [HHb] using a continueswave fNIRS device at large source-detector separation, while superficial blood flow was stimulated by infrared lasers. A mesh-based Monte Carlo code was applied to estimate fNIRS sensitivity to superficial hemodynamic changes in a realistic 3D MRI-based brain phantom. Results: First, we simulated photon migration in a four-layered human-head slab model to calculate PPLs and fNIRS sensitivity. Then, the localization of the infrared laser inside a realistic brain model was studied using the Monte Carlo method. Finally, the changes in [HHb] over the prefrontal cortex of six adult males were measured by fNIRS at a source-detector separation of 3 cm. The results demonstrated that the relation between fNIRS sensitivity and an increase in S-D separation was nonlinear and a correlation between shallow and deep signals was observed. Conclusion: The presented results demonstrated that the temporal changes in the superficial blood flow could strongly affect HHb measurement at large source-detector separation. Hence, the cerebral activity map extracted from the [HHb] signal was mainly contaminated by superficial blood flow.

Investigation of the source-detector separation in near infrared spectroscopy for healthy and clinical applications

Understanding near infrared light propagation in tissue is vital for designing next generation optical brain imaging devices. Monte Carlo (MC) simulations provide a controlled mechanism to characterize and evaluate contributions of diverse near infrared spectroscopy (NIRS) sensor configurations and parameters. In this study, we developed a multilayer adult digital head model under both healthy and clinical settings and assessed light-tissue interaction through MC simulations in terms of partial differential pathlength, mean total optical pathlength, diffuse reflectance, detector light intensity and spatial sensitivity profile of optical measurements. The model incorporated four layers: scalp, skull, cerebrospinal-fluid and cerebral cortex with and without a customizable lesion for modeling hematoma of different sizes and depths. The effect of source-detector separation (SDS) on optical measurements' sensitivity to brain tissue was investigated. Results from 1330 separate simulations [(4 lesion volumes × 4 lesion depths for clinical +3 healthy settings) × 7 SDS × 10 simulation = 1330)] each with 100 million photons indicated that selection of SDS is critical to acquire optimal measurements from the brain and recommended SDS to be 25 to 35 mm depending on the wavelengths to obtain optical monitoring of the adult brain function. The findings here can guide the design of future NIRS probes for functional neuroimaging and clinical diagnostic systems.

Pre-operative Brain Imaging Using Functional Near-Infrared Spectroscopy Helps Predict Cochlear Implant Outcome in Deaf Adults

Currently, it is not possible to accurately predict how well a deaf individual will be able to understand speech when hearing is (re)introduced via a cochlear implant. Differences in brain organisation following deafness are thought to contribute to variability in speech understanding with a cochlear implant and may offer unique insights that could help to more reliably predict outcomes. An emerging optical neuroimaging technique, functional near-infrared spectroscopy (fNIRS), was used to determine whether a pre-operative measure of brain activation could explain variability in cochlear implant (CI) outcomes and offer additional prognostic value above that provided by known clinical characteristics. Cross-modal activation to visual speech was measured in bilateral superior temporal cortex of pre- and post-lingually deaf adults before cochlear implantation. Behavioural measures of auditory speech understanding were obtained in the same individuals following 6 months of cochlear implant use. The results showed that stronger pre-operative cross-modal activation of auditory brain regions by visual speech was predictive of poorer auditory speech understanding after implantation. Further investigation suggested that this relationship may have been driven primarily by the inclusion of, and group differences between, pre- and post-lingually deaf individuals. Nonetheless, pre-operative cortical imaging provided additional prognostic value above that of influential clinical characteristics, including the age-at-onset and duration of auditory deprivation, suggesting that objectively assessing the physiological status of the brain using fNIRS imaging pre-operatively may support more accurate prediction of individual CI outcomes. Whilst activation of auditory brain regions by visual speech prior to implantation was related to the CI user's clinical history of deafness, activation to visual speech did not relate to the future ability of these brain regions to respond to auditory speech stimulation with a CI. Greater pre-operative activation of left superior temporal cortex by visual speech was associated with enhanced speechreading abilities, suggesting that visual speech processing may help to maintain left temporal lobe specialisation for language processing during periods of profound deafness.

Maternal speech shapes the cerebral frontotemporal network in neonates: A hemodynamic functional connectivity study

Language development and the capacity for communication in infants are predominantly supported by their mothers, beginning when infants are still in utero. Although a mother's speech should thus have a significant impact on her neonate's brain, neurocognitive evidence for this hypothesis remains elusive. The present study examined 37 neonates using near-infrared spectroscopy and observed the interactions between multiple cortical regions while neonates heard speech spoken by their mothers or by strangers. We analyzed the functional connectivity between regions whose response-activation patterns differed between the two types of speakers. We found that when hearing their mothers' speech, functional connectivity was enhanced in both the neonatal left and right frontotemporal networks. On the left it was enhanced between the inferior/middle frontal gyrus and the temporal cortex, while on the right it was enhanced between the frontal pole and temporal cortex. In particular, the frontal pole was more strongly connected to the left supramarginal area when hearing speech from mothers. These enhanced frontotemporal networks connect areas that are associated with language (left) and voice processing (right) at later stages of development. We suggest that these roles are initially fostered by maternal speech.

Evaluating time-reversed speech and signal-correlated noise as auditory baselines for isolating speech-specific processing using fNIRS

Evidence using well-established imaging techniques, such as functional magnetic resonance imaging and electrocorticography, suggest that speech-specific cortical responses can be functionally localised by contrasting speech responses with an auditory baseline stimulus, such as time-reversed (TR) speech or signal-correlated noise (SCN). Furthermore, these studies suggest that SCN is a more effective baseline than TR speech. Functional near-infrared spectroscopy (fNIRS) is a relatively novel, optically-based imaging technique with features that make it ideal for investigating speech and language function in paediatric populations. However, it is not known which baseline is best at isolating speech activation when imaging using fNIRS. We presented normal speech, TR speech and SCN in an event-related format to 25 normally-hearing children aged 6-12 years. Brain activity was measured across frontal and temporal brain areas in both cerebral hemispheres whilst children passively listened to the auditory stimuli. In all three conditions, significant activation was observed bilaterally in channels targeting superior temporal regions when stimuli were contrasted against silence. Unlike previous findings in infants, we found no significant activation in the region of interest over superior temporal cortex in school-age children when normal speech was contrasted against either TR speech or SCN. Although no statistically significant lateralisation effects were observed in the region of interest, a left-sided channel targeting posterior temporal regions showed significant activity in response to normal speech only, and was investigated further. Significantly greater activation was observed in this left posterior channel compared to the corresponding channel on the right side under the normal speech vs SCN contrast only. Our findings suggest that neither TR speech nor SCN are suitable auditory baselines for functionally isolating speech-specific processing in an experimental set up involving fNIRS with 6-12 year old children.

Cancellation of Superficial Blood Flow in Brain Function Measurements Using Near-Infrared Spectroscopy

In brain function measurement by near-infrared spectroscopy, reduction of signal fluctuation caused by the superficial blood flow is necessary. We proposed an equilateral-triangle-type sensor arrangement for cancelling superficial blood flow using short-distance detectors placed at the center of the triangle. We applied the independent components analysis (ICA) for this equilateral triangle configuration to improve the correction effect. We measured the change in blood volume caused by the motion artifacts according to the posture change and analyzed the correction effect of the ICA. It is shown that the ICA is more effective than simple subtraction and has small dependence on the measurement conditions and is applicable to this equilateral triangle configuration.

Emotion-related cerebral blood flow changes in the ventral medial prefrontal cortex: An NIRS study

The current study examined whether cerebral blood flow (CBF) changes in the anterior ventral medial prefrontal cortex (VMPFC) represent responses to emotional stimuli instead of cognitive control of emotion during distraction tasks, as suggested by our previous near-infrared spectroscopy (NIRS) study. The functional distinction of MPFC regions is occasionally difficult due to their multiple functions. Here, we addressed some remaining concerns from our previous distraction studies, and employed the distraction paradigm, in which negative or neutral images are presented as emotional stimuli; a rest period is included in one condition and working memory (distraction) tasks in the other. To extract the components of CBF changes associated with responses to negative emotional stimuli (defined as emotion-related CBF changes), we subtracted the CBF changes obtained in the neutral condition from those in the negative condition. We found that emotion-related CBF changes in the anterior left VMPFC were significantly greater in the rest condition than in the distraction task condition. These findings imply that the distraction task decreased unnecessary brain activities, resulting in decrease in the emotion-related CBF changes. They support our previous findings, indicating that CBF changes in anterior VMPFC regions, measured using NIRS, are specifically associated with responses to emotional stimuli.

Cortical Speech Processing in Postlingually Deaf Adult Cochlear Implant Users, as Revealed by Functional Near-Infrared Spectroscopy

An experiment was conducted to investigate the feasibility of using functional near-infrared spectroscopy (fNIRS) to image cortical activity in the language areas of cochlear implant (CI) users and to explore the association between the activity and their speech understanding ability. Using fNIRS, 15 experienced CI users and 14 normal-hearing participants were imaged while presented with either visual speech or auditory speech. Brain activation was measured from the prefrontal, temporal, and parietal lobe in both hemispheres, including the language-associated regions. In response to visual speech, the activation levels of CI users in an a priori region of interest (ROI)—the left superior temporal gyrus or sulcus—were negatively correlated with auditory speech understanding. This result suggests that increased cross-modal activity in the auditory cortex is predictive of poor auditory speech understanding. In another two ROIs, in which CI users showed significantly different mean activation levels in response to auditory speech compared with normal-hearing listeners, activation levels were significantly negatively correlated with CI users’ auditory speech understanding. These ROIs were located in the right anterior temporal lobe (including a portion of prefrontal lobe) and the left middle superior temporal lobe. In conclusion, fNIRS successfully revealed activation patterns in CI users associated with their auditory speech understanding.

Socioeconomic disparity in prefrontal development during early childhood

Socioeconomic status (SES) has a powerful influence on cognitive, social and brain development. Children from low-SES backgrounds show poor executive function (EF). However, it is unclear if there is a SES-dependent disparity in functional brain development. The present study examined whether the SES of preschool children (N = 93) is associated with prefrontal activation during cognitive shifting tasks as measured by near-infrared spectroscopy. Low-SES children did not show activation in lateral prefrontal regions during the tasks, whereas middle- and high-SES children showed prefrontal activations, although no differences were found in terms of behavioural performance. These results suggest that SES can affect the functional development of the prefrontal regions. In this study, we discuss the practical implications of the results.

Denoising of neuronal signal from mixed systemic low-frequency oscillation using peripheral measurement as noise regressor in near-infrared imaging

Functional near-infrared spectroscopy (fNIRS) is a noninvasive functional imaging technique measuring hemodynamic changes including oxygenated ( O 2 Hb ) and deoxygenated (HHb) hemoglobin. Low frequency (LF; 0.01 to 0.15 Hz) band is commonly analyzed in fNIRS to represent neuronal activation. However, systemic physiological artifacts (i.e., nonneuronal) likely occur also in overlapping frequency bands. We measured peripheral photoplethysmogram (PPG) signal concurrently with fNIRS (at prefrontal region) to extract the low-frequency oscillations (LFOs) as systemic noise regressors. We investigated three main points in this study: (1) the relationship between prefrontal fNIRS and peripheral PPG signals; (2) the denoising potential using these peripheral LFOs, and (3) the innovative ways to avoid the false-positive result in fNIRS studies. We employed spatial working memory (WM) and control tasks (e.g., resting state) to illustrate these points. Our results showed: (1) correlation between signals from prefrontal fNIRS and peripheral PPG is region-dependent. The high correlation with peripheral ear signal (i.e., O 2 Hb ) occurred mainly in frontopolar regions in both spatial WM and control tasks. This may indicate the finding of task-dependent effect even in peripheral signals. We also found that the PPG recording at the ear has a high correlation with prefrontal fNIRS signal than the finger signals. (2) The systemic noise was reduced by 25% to 34% on average across regions, with a maximum of 39% to 58% in the highly correlated frontopolar region, by using these peripheral LFOs as noise regressors. (3) By performing the control tasks, we confirmed that the statistically significant activation was observed in the spatial WM task, not in the controls. This suggested that systemic (and any other) noises unlikely violated the major statistical inference. (4) Lastly, by denoising using the task-related signals, the significant activation of region-of-interest was still observed suggesting the manifest task-evoked response in the spatial WM task.

Using Brain Activation to Evaluate Arrangements Aiding Hand-Eye Coordination in Surgical Robot Systems

GOAL

To realize intuitive, minimally invasive surgery, surgical robots are often controlled using master-slave systems. However, the surgical robot's structure often differs from that of the human body, so the arrangement between the monitor and master must reflect this physical difference. In this study, we validate the feasibility of an embodiment evaluation method that determines the arrangement between the monitor and master. In our constructed cognitive model, the brain's intraparietal sulcus activates significantly when somatic and visual feedback match. Using this model, we validate a cognitively appropriate arrangement between the monitor and master.

METHODS

In experiments, we measure participants' brain activation using an imaging device as they control the virtual surgical simulator. Two experiments are carried out that vary the monitor and hand positions.

CONCLUSION

There are two common arrangements of the monitor and master at the brain activation's peak: One is placing the monitor behind the master, so the user feels that the system is an extension of his arms into the monitor; the other arranges the monitor in front of the master, so the user feels the correspondence between his own arm and the virtual arm in the monitor.

SIGNIFICANCE

From these results, we conclude that the arrangement between the monitor and master impacts embodiment, enabling the participant to feel apparent posture matches in master-slave surgical robot systems.

Effects of oral ingestion on physical functions before tube feeding in adults with severe motor and intellectual disabilities

This study aimed to determine the significance of oral ingestion in tube-fed adults. Six males and three females (mean age 48.1 ± 12.4 years) with severe motor and intellectual disabilities were included in this study. The subjects were monitored for cerebral blood flow (CBF) by functional near-infrared spectroscopy imaging, gastric motor function by electrogastrography, and arterial oxygen saturation (SpO₂) and pulse rate with a biological data monitoring device. The subjects were divided into two groups, settings A and B. In setting A, after resting for 30 min, the subjects were tube fed a routinely used enteral nutrient solution. In Setting B, the subjects received 10 cc of thickened enteral nutrient solution prior to tube feeding. Cerebral function as measured by CBF significantly increased after tube feeding under setting A (without oral ingestion), as compared to the resting state. Under setting B (with oral ingestion), CBF significantly increased after oral ingestion and after tube feeding. SpO₂ significantly decreased under setting B after oral ingestion and after tube feeding. Gastric motor function showed no significant change after tube feeding in either setting. The pulse rate significantly increased before tube feeding as compared to that in the resting state, after feeding as compared to before feeding and after feeding as compared to the resting state. Our data suggest that introducing oral ingestion, at least partially, in tube-fed individuals with severe dysphagia is beneficial in that it can stimulate cerebral function.

Acute Stress Attenuates Cognitive Flexibility in Males Only: An fNIRS Examination

Cognitive processes that afford us the ability to control thoughts and achieve goal-directed behavior are known as executive functions. Empirical evidence in the past few years has demonstrated that executive functions can be influenced by acute stress. The impact of acute stress on cognitive flexibility, a key aspect of executive functions, has received little attention in the literature. We present the results of two experiments conducted to examine the effect of acute stress on cognitive flexibility. Acute stress was induced using the cold pressor task. Cognitive flexibility was assessed using the Wisconsin Card Sorting Test (WCST). Across both experiments acute stress had an attenuating effect on task switching on the WCST. Our findings also indicate that this effect was moderated by the participant’s gender. In Study 1, we observed that following stress exposure male participants in the stress condition made more perseverative errors than participants in the control group. In Study 2, we examined the bilateral hemodynamics in the prefrontal cortex (PFC) during acute stress induction using functional near infrared spectroscopy (fNIRS). Our analysis indicated that functional oxyHb signals fluctuated with greater amplitude than systemic components for participants in the stress group relative to those in the control group. In addition, oxyHb levels post stress induction were correlated with performance on the WCST for the male participants in the stress group only. Concordant with previous reports, our findings indicate that acute stress impacts cognitive flexibility in males and females differentially. Our work also demonstrates the feasibility of using fNIRS as a practical and objective technique for the examination of hemodynamics in the PFC during acute stress.

Investigation of the Pattern of the Hemodynamic Response as Measured by Functional Near-Infrared Spectroscopy (fNIRS) Studies in Newborns, Less Than a Month Old: A Systematic Review

It has been 20 years since functional near-infrared spectroscopy (fNIRS) was first used to investigate the evoked hemodynamic response to a stimulus in newborns. The hemodynamic response to functional activation is well-established in adults, with an observed increase in concentration change of oxygenated hemoglobin (Δ[HbO2]) and decrease in deoxygenated hemoglobin (Δ[HHb]). However, functional studies in newborns have revealed a mixed response, particularly with Δ[HHb] where an inconsistent change in direction is observed. The reason for this heterogeneity is unknown, with potential explanations arising from differing physiology in the developing brain, or differences in instrumentation or methodology. The aim of this review is to collate the findings from studies that have employed fNIRS to monitor cerebral hemodynamics in term newborn infants aged 1 day-1 month. A total of 46 eligible studies were identified; some studies investigated more than one stimulus type, resulting in a total of 51 reported results. The NIRS parameters reported varied across studies with 50/51 cases reporting Δ[HbO2], 39/51 reporting Δ[HHb], and 13/51 reporting total hemoglobin concentration Δ[HbT] (Δ[HbO2] + Δ[HHb]). However, of the 39 cases reporting Δ[HHb] in graphs or tables, only 24 studies explicitly discussed the response (i.e., direction of change) of this variable. In the studies where the fNIRS responses were discussed, 46/51 cases observed an increase in Δ[HbO2], 7/51 observed an increase or varied Δ[HHb], and 2/51 reported a varied or negative Δ[HbT]. An increase in Δ[HbO2] and decrease or no change in Δ[HHb] was observed in 15 studies. By reviewing this body of literature, we have identified that the majority of research articles reported an increase in Δ[HbO2] across various functional tasks and did not report the response of Δ[HHb]. Confirming the normal, healthy hemodynamic response in newborns will allow identification of unhealthy patterns and their association to normal neurodevelopment.

Impact of Healthy Aging on Multifractal Hemodynamic Fluctuations in the Human Prefrontal Cortex

Fluctuations in resting-state cerebral hemodynamics show scale-free behavior over two distinct scaling ranges. Changes in such bimodal (multi) fractal pattern give insight to altered cerebrovascular or neural function. Our main goal was to assess the distribution of local scale-free properties characterizing cerebral hemodynamics and to disentangle the influence of aging on these multifractal parameters. To this end, we obtained extended resting-state records (N = 2¹⁴) of oxyhemoglobin (HbO), deoxyhemoglobin (HbR) and total hemoglobin (HbT) concentration time series with continuous-wave near-infrared spectroscopy technology from the brain cortex. 52 healthy volunteers were enrolled in this study: 24 young (30.6 ± 8.2 years), and 28 elderly (60.5 ± 12.0 years) subjects. Using screening tests on power-law, multifractal noise, and shuffled data sets we evaluated the presence of true multifractal hemodynamics reflecting long-range correlation (LRC). Subsequently, scaling-range adaptive bimodal signal summation conversion (SSC) was performed based on standard deviation (σ) of signal windows across a range of temporal scales (s). Building on moments of different order (q) of the measure, σ(s), multifractal SSC yielded generalized Hurst exponent function, H(q), and singularity spectrum, D(h) separately for a fast and slow component (the latter dominating the highest temporal scales). Parameters were calculated reflecting the estimated measure at s = N (focus), degree of LRC [Hurst exponent, H(2) and maximal Hölder exponent, h_max] and measuring strength of multifractality [full-width-half-maximum of D(h) and ΔH₁₅ = H(−15)−H(15)]. Correlation-based signal improvement (CBSI) enhanced our signal in terms of interpreting changes due to neural activity or local/systemic hemodynamic influences. We characterized the HbO-HbR relationship with the aid of fractal scale-wise correlation coefficient, r_σ(s) and SSC-based multifractal covariance analysis. In the majority of subjects, cerebral hemodynamic fluctuations proved bimodal multifractal. In case of slow component of raw HbT, h_max, and Ĥ(2) were lower in the young group explained by a significantly increased r_σ(s) among elderly at high temporal scales. Regarding the fast component of CBSI-pretreated HbT and that of HbO-HbR covariance, h_max, and focus were decreased in the elderly group. These observations suggest an attenuation of neurovascular coupling reflected by a decreased autocorrelation of the neuronal component concomitant with an accompanying increased autocorrelation of the non-neuronal component in the elderly group.

Functional near-infrared spectroscopy for monitoring macaque cerebral motor activity during voluntary movements without head fixation

We developed an fNIRS system for monitoring macaque cerebral motor activity during voluntary movements without head fixation. fNIRS data at 27 channels in 7.5 mm spatial interval were calibrated by simulating light propagation through the macaque cranial tissues. The subject was instructed to repeatedly (75 times) retrieve a food pellet with alternating left or right hands from a food well for each session. We detected significant increases in oxygenated hemoglobin (Hb) and decrease in deoxygenated Hb in the primary motor area (M1) contralateral to the hand used. In more rostral and ventral regions in both hemispheres, the hemodynamic similarly changed regardless of used hand. Direct feeding to the mouth eliminated activity in the hand M1 whereas that at bilateral ventral regions (mouth M1 area) remained. Statistical analyses for the hemodynamics between left/right-hand use revealed the location of each hand M1 in either hemisphere. In these regions, the maximum amplitude and time of the maximum amplitude in the hemodynamic response evoked by food retrieval were highly correlated with the time associated with food retrieval. We could assign each channel to an appropriate functional motor area, providing proof of principle for future studies involving brain damage models in freely moving macaque monkeys.

Cancellation Method of Signal Fluctuations in Brain Function Measurements Using Near-Infrared Spectroscopy

To estimate brain activity, it is important to improve the accuracy of brain function measurements by using near-infrared spectroscopy. The detection of signals is vital for correcting any disturbances or changes in the skin blood volume. We developed a cancellation method for brain probes placed on the scalp in the configuration of an equilateral triangle. In this configuration, 12 types of target signals were detected between the vertices, and 6 types of correction signals were detected between the vertices and the center of the triangle. We measured the changes in the blood volume resulting from the specific postural changes of the subject and applied the correction method using three calculation methods. The measured results showed that the correction signals were effective in reducing the disturbances. The correction was based on the cross-correlation coefficient and the amplitude ratio of signals.

FNIRS activity in the prefrontal cortex and motivational intensity: impact of working memory load, financial reward, and correlation-based signal improvement

Previous research has demonstrated changes in neurovascular activation of the prefrontal cortex to increased working memory load. The primary purpose of the current paper was to investigate overload of working memory capacity using functional near-infrared spectroscopy (fNIRS) within the framework of motivational intensity theory. A secondary goal was to explore the influence of the correlation-based signal improvement (CBSI) as a method for correcting the influence of systemic variables. In study one, 30 participants (15 female, mean age = 21.09 years, s.d. = 2.9 years) performed a verbal version of the n -back working memory task under four levels of demand (easy, hard, very hard, and impossible). In contrast to the raw data, CBSI-transformed fNIRS data indicated that neurovascular coupling was highest at hard demand when the task was challenging but success was possible. The second study ( N=30 ; 15 female, mean age = 22.4 years, s.d. = 5.3) replicated the working memory manipulation with the addition of low versus high levels of financial reward. Analyses of CBSI-transformed levels of oxygenated (HbO) and deoxygenated (HHb) hemoglobin replicated the first study at right lateral regions of the prefrontal cortex (BA46). HHb_CBSI data were significantly reduced at impossible demand for participants receiving the higher level of financial reward. The study is the first to support predictions from the motivational intensity model using neurovascular data. In addition, the application of CBSI to fNIRS data was found to improve the sensitivity of HbO and Hbb to the independent variables.

Excessive hemodynamic activity in the superior frontal cortex during the flanker task in children with attention deficit hyperactivity disorder

Near-infrared spectroscopy studies in children with attention deficit hyperactivity disorder (ADHD) have shown excessive prefrontal activity responsible for coping with interference. However, it is possible that the previous results were influenced by verbal, reading, and memory developments. The flanker task is an interference task that does not require a verbal response, reading, or memorization. We examined activity in the superior frontal cortex (SFC) during the flanker task in 12 children with ADHD and 14 children with typical development using near-infrared spectroscopy. SFC activity was significantly greater in children with ADHD than in those with typical development. The results showed excessive interference coping activity in children with ADHD irrespective of verbal, reading, and memory development. Moreover, SFC activity was positively correlated with the inattention subscale score of the ADHD rating scale. We suggest that children with ADHD need greater SFC activation to cope with interference, and the inefficient mechanism is demanding and hard to sustain, which causes inattention symptoms of children with ADHD.

Relationships Between Gum Chewing and Stroop Test: A Pilot Study

Cognitive function tends to decrease with aging, therefore maintenance of this function in an aging society is an important issue. The role of chewing in nutrition is important. Although several studies indicate that gum chewing is thought to improve cognitive function, it remains debatable whether gum-chewing does in fact improve cognitive function. The Stroop test is a psychological tool used to measure cognition. A shorter reaction time indicates a mean higher behavioral performance and higher levels of oxy-Hb concentration. fNIRS is a powerful, non-invasive imaging technique offering many advantages, including compact size, no need for specially equipped facilities, and the potential for real-time measurement. The left dorsolateral prefrontal cortex (DLPFC) seems to be mainly involved in the Stroop task.The aim of the present study was to investigate the hypothesis that gum-chewing changes cerebral blood flow in the left DLPFC during the Stroop test, and also changes the reaction time. Fourteen healthy volunteers (mean age 26.9 years) participated in this study after providing written informed consent. A piece of tasteless gum weighing 1.0 g was used. Each session was designed in a block manner, i.e. 4 rests (30 s) and 3 blocks of task (30 s). A computerized Stroop test was used (including both congruent and incongruent Stroop tasks) which calculates a response time automatically. The Binominal test was used for comparisons (p < 0.05). The results show activation of the left DLPFC during the Stroop task and that gum chewing significantly increases responses/oxy-Hb concentration and significantly shortens the reaction time.

Signal Processing in Functional Near-Infrared Spectroscopy (fNIRS): Methodological Differences Lead to Different Statistical Results

Even though research in the field of functional near-infrared spectroscopy (fNIRS) has been performed for more than 20 years, consensus on signal processing methods is still lacking. A significant knowledge gap exists between established researchers and those entering the field. One major issue regularly observed in publications from researchers new to the field is the failure to consider possible signal contamination by hemodynamic changes unrelated to neurovascular coupling (i.e., scalp blood flow and systemic blood flow). This might be due to the fact that these researchers use the signal processing methods provided by the manufacturers of their measurement device without an advanced understanding of the performed steps. The aim of the present study was to investigate how different signal processing approaches (including and excluding approaches that partially correct for the possible signal contamination) affect the results of a typical functional neuroimaging study performed with fNIRS. In particular, we evaluated one standard signal processing method provided by a commercial company and compared it to three customized approaches. We thereby investigated the influence of the chosen method on the statistical outcome of a clinical data set (task-evoked motor cortex activity). No short-channels were used in the present study and therefore two types of multi-channel corrections based on multiple long-channels were applied. The choice of the signal processing method had a considerable influence on the outcome of the study. While methods that ignored the contamination of the fNIRS signals by task-evoked physiological noise yielded several significant hemodynamic responses over the whole head, the statistical significance of these findings disappeared when accounting for part of the contamination using a multi-channel regression. We conclude that adopting signal processing methods that correct for physiological confounding effects might yield more realistic results in cases where multi-distance measurements are not possible. Furthermore, we recommend using manufacturers' standard signal processing methods only in case the user has an advanced understanding of every signal processing step performed.

Effect of the COMT Val158Met genotype on lateral prefrontal activations in young children

Low executive function (EF) during early childhood is a major risk factor for developmental delay, academic failure, and social withdrawal. Susceptible genes may affect the molecular and biological mechanisms underpinning EF. More specifically, genes associated with the regulation of prefrontal dopamine may modulate the response of prefrontal neurons during executive control. Several studies with adults and older children have shown that variants of the catechol‐O‐methyltransferase (COMT) gene are associated with behavioral performance and prefrontal activations in EF tasks. However, the effect of the COMT genotype on prefrontal activations during EF tasks on young children is still unknown. The present study examined whether a common functional polymorphism (Val158Met) in the COMT gene was associated with prefrontal activations and cognitive shifting in 3‐ to 6‐year‐old children. The study revealed that, compared with children with at least one Met allele (Met/Met and Met/Val), children who were Val homozygous (i) were more able to flexibly switch rules in cognitive shifting tasks and (ii) exhibited increased activations in lateral prefrontal regions during these tasks. This is the first evidence that demonstrates the relationship between a gene polymorphism and prefrontal activations in young children. It also indicates that COMT Val homozygosity may be advantageous for cognitive shifting and prefrontal functions, at least during early childhood, and children who possess this variant may have a lower risk of developing future cognitive and social development issues.

Listening in Naturalistic Scenes: What Can Functional Near-Infrared Spectroscopy and Intersubject Correlation Analysis Tell Us About the Underlying Brain Activity?

Listening to speech in the noisy conditions of everyday life can be effortful, reflecting the increased cognitive workload involved in extracting meaning from a degraded acoustic signal. Studying the underlying neural processes has the potential to provide mechanistic insight into why listening is effortful under certain conditions. In a move toward studying listening effort under ecologically relevant conditions, we used the silent and flexible neuroimaging technique functional near-infrared spectroscopy (fNIRS) to examine brain activity during attentive listening to speech in naturalistic scenes. Thirty normally hearing participants listened to a series of narratives continuously varying in acoustic difficulty while undergoing fNIRS imaging. Participants then listened to another set of closely matched narratives and rated perceived effort and intelligibility for each scene. As expected, self-reported effort generally increased with worsening signal-to-noise ratio. After controlling for better-ear signal-to-noise ratio, perceived effort was greater in scenes that contained competing speech than in those that did not, potentially reflecting an additional cognitive cost of overcoming informational masking. We analyzed the fNIRS data using intersubject correlation, a data-driven approach suitable for analyzing data collected under naturalistic conditions. Significant intersubject correlation was seen in the bilateral auditory cortices and in a range of channels across the prefrontal cortex. The involvement of prefrontal regions is consistent with the notion that higher order cognitive processes are engaged during attentive listening to speech in complex real-world conditions. However, further research is needed to elucidate the relationship between perceived listening effort and activity in these extended cortical networks.

Signal processing of functional NIRS data acquired during overt speaking

Functional near-infrared spectroscopy (fNIRS) offers an advantage over traditional functional imaging methods [such as functional magnetic resonance imaging (fMRI)] by allowing participants to move and speak relatively freely. However, neuroimaging while actively speaking has proven to be particularly challenging due to the systemic artifacts that tend to be located in the critical brain areas. To overcome these limitations and enhance the utility of fNIRS, we describe methods for investigating cortical activity during spoken language tasks through refinement of deoxyhemoglobin (deoxyHb) signals with principal component analysis (PCA) spatial filtering to remove global components. We studied overt picture naming and compared oxyhemoglobin (oxyHb) and deoxyHb signals with and without global component removal using general linear model approaches. Activity in Broca's region and supplementary motor cortex was observed only when the filter was applied to the deoxyHb signal and was shown to be spatially comparable to fMRI data acquired using a similar task and to meta-analysis data. oxyHb signals did not yield expected activity in Broca's region with or without global component removal. This study demonstrates the utility of a PCA spatial filter on the deoxyHb signal in revealing neural activity related to a spoken language task and extends applications of fNIRS to natural and ecologically valid conditions.

Adaptive benefit of cross-modal plasticity following cochlear implantation in deaf adults

It has been suggested that visual language is maladaptive for hearing restoration with a cochlear implant (CI) due to cross-modal recruitment of auditory brain regions. Rehabilitative guidelines therefore discourage the use of visual language. However, neuroscientific understanding of cross-modal plasticity following cochlear implantation has been restricted due to incompatibility between established neuroimaging techniques and the surgically implanted electronic and magnetic components of the CI. As a solution to this problem, here we used functional near-infrared spectroscopy (fNIRS), a noninvasive optical neuroimaging method that is fully compatible with a CI and safe for repeated testing. The aim of this study was to examine cross-modal activation of auditory brain regions by visual speech from before to after implantation and its relation to CI success. Using fNIRS, we examined activation of superior temporal cortex to visual speech in the same profoundly deaf adults both before and 6 mo after implantation. Patients' ability to understand auditory speech with their CI was also measured following 6 mo of CI use. Contrary to existing theory, the results demonstrate that increased cross-modal activation of auditory brain regions by visual speech from before to after implantation is associated with better speech understanding with a CI. Furthermore, activation of auditory cortex by visual and auditory speech developed in synchrony after implantation. Together these findings suggest that cross-modal plasticity by visual speech does not exert previously assumed maladaptive effects on CI success, but instead provides adaptive benefits to the restoration of hearing after implantation through an audiovisual mechanism.

The relationship between the superior frontal cortex and alpha oscillation in a flanker task: Simultaneous recording of electroencephalogram (EEG) and near infrared spectroscopy (NIRS)

Activity in the alpha band of the electroencephalogram (EEG) reflects functional inhibition of the cerebral cortex. The superior frontal cortex (SFC) is known to control alpha activity. Based on this relationship between SFC and alpha, we hypothesized that SFC controlled alpha mediates proactive control over interference. In this study, we examined the relationship between SFC and alpha in the flanker task by simultaneously recording EEG and near infrared spectroscopy (NIRS). Forty participants performed a flanker task with occasional (compatible 75%, incompatible 25%) and successive (incompatible 100%) conditions. In the occasional condition, larger SFC activity was related to pre-stimulus alpha enhancement under occipital electrodes. This is consistent with a model in which SFC enhances pre-stimulus alpha activity, leading to proactive control over interference. However, we could not detect a correlation between SFC activity and alpha activity in the successive condition. Active inhibition may have been reduced by a need to continuously inhibit brain regions associated with the irrelevant information. This may have reduced the role of the SFC in controlling alpha activity. Based on these findings, we postulate that there are two cerebral mechanisms of proactive control over interference.

Increased prefrontal cortex connectivity during cognitive challenge assessed by fNIRS imaging

In this study, functional near-infrared spectroscopy (fNIRS) and the graph theory approach were used to access the functional connectivity (FC) of the prefrontal cortex (PFC) in a resting state and during increased mental workload. For this very purpose, a pattern recognition-based test was developed, which elicited a strong response throughout the PFC during the test condition. FC parameters obtained during stimulation were found increased compared to those in a resting state after correlation based signal improvement (CBSI), which can attenuate those components of fNIRS signals which are unrelated to neural activity. These results indicate that the cognitive challenge increased the FC in the PFC and suggests a great potential in investigating FC in various cognitive states.

Measuring cortical motor hemodynamics during assisted stepping - An fNIRS feasibility study of using a walker

Walkers are commonly prescribed worldwide to individuals unable to walk independently. Walker usage leads to improved postural control and voluntary movement during step. In the present study, we aimed to provide a concept-proof on the feasibility of an event-related protocol integrating the analyses of biomechanical variables of step initiation and functional near-infrared spectroscopy (fNIRS) to measure activation of the supplementary motor area (SMA) while using a walker. Healthy young participants were tested while stepping with versus without the use of the walker. Behavioral analysis showed that anticipatory postural adjustments (APA) decreased when supporting the body weight on the walker. Delta (without-with) of activation magnitude of the muscle tibialis anterior was positively correlated to the delta of deoxyhemoglobin concentration changes in the SMA. The novelty of this study is the development of a protocol to assess brain function together with biomechanical analysis during the use of a walker. The method sheds light to the potential utility of combining fNIRS and biomechanical assessment during assistive step initiation, which can represent a new opportunity to study populations with mobility deficits.

Effect of confounding variables on hemodynamic response function estimation using averaging and deconvolution analysis: An event-related NIRS study

Slow and rapid event-related designs are used in fMRI and functional near-infrared spectroscopy (fNIRS) experiments to temporally characterize the brain hemodynamic response to discrete events. Conventional averaging (CA) and the deconvolution method (DM) are the two techniques commonly used to estimate the Hemodynamic Response Function (HRF) profile in event-related designs. In this study, we conducted a series of simulations using synthetic and real NIRS data to examine the effect of the main confounding factors, including event sequence timing parameters, different types of noise, signal-to-noise ratio (SNR), temporal autocorrelation and temporal filtering on the performance of these techniques in slow and rapid event-related designs. We also compared systematic errors in the estimates of the fitted HRF amplitude, latency and duration for both techniques. We further compared the performance of deconvolution methods based on Finite Impulse Response (FIR) basis functions and gamma basis sets. Our results demonstrate that DM was much less sensitive to confounding factors than CA. Event timing was the main parameter largely affecting the accuracy of CA. In slow event-related designs, deconvolution methods provided similar results to those obtained by CA. In rapid event-related designs, our results showed that DM outperformed CA for all SNR, especially above -5 dB regardless of the event sequence timing and the dynamics of background NIRS activity. Our results also show that periodic low-frequency systemic hemodynamic fluctuations as well as phase-locked noise can markedly obscure hemodynamic evoked responses. Temporal autocorrelation also affected the performance of both techniques by inducing distortions in the time profile of the estimated hemodynamic response with inflated t-statistics, especially at low SNRs. We also found that high-pass temporal filtering could substantially affect the performance of both techniques by removing the low-frequency components of HRF profiles. Our results emphasize the importance of characterization of event timing, background noise and SNR when estimating HRF profiles using CA and DM in event-related designs.

Impact of communicative head movements on the quality of functional near-infrared spectroscopy signals: negligible effects for affirmative and negative gestures and consistent artifacts related to raising eyebrows

Functional near-infrared spectroscopy (fNIRS) is currently one of the most promising tools in the neuroscientific research to study brain hemodynamics during naturalistic social communication. The application of fNIRS by studies in this field of knowledge has been widely justified by its strong resilience to motion artifacts, including those that might be generated by communicative head and facial movements. Previous studies have focused on the identification and correction of these artifacts, but a quantification of the differential contribution of common communicative movements on the quality of fNIRS signals is still missing. We assessed the impact of four movements (nodding head up and down, reading aloud, nodding head sideways, and raising eyebrows) performed during rest and task conditions on two metrics of signal quality control: an estimative of signal-to-noise performance and the negative correlation between oxygenated and deoxygenated hemoglobin (oxy-Hb and deoxy-Hb). Channel-wise group analysis confirmed the robustness of the fNIRS technique to head nodding movements but showed a large effect of raising eyebrows in both signal quality control metrics, both during task and rest conditions. Reading aloud did not disrupt the expected anticorrelation between oxy-Hb and deoxy-Hb but had a relatively large effect on signal-to-noise performance. These findings may have implications to the interpretation of fNIRS studies examining communicative processes.

Lawrence K. Subtraction-based approach for enhancing the depth sensitivity of time-resolved NIRS

The aim of this study was to evaluate enhancing of the depth sensitivity of time-resolved near-infrared spectroscopy with a subtraction-based approach. Due to the complexity of light propagation in a heterogeneous media, and to prove the validity of the proposed method in a heterogeneous turbid media we conducted a broad analysis taking into account a number of parameters related to the method as well as various parameters of this media. The results of these experiments confirm that the depth sensitivity of the subtraction-based approach is better than classical approaches using continuous-wave or time-resolved methods. Furthermore, the results showed that the subtraction-based approach has a unique, selective sensitivity to a layer at a specific depth. In vivo application of the proposed method resulted in a greater magnitude of the hemodynamic changes during functional activation than with the standard approach.

Speech-evoked activation in adult temporal cortex measured using functional near-infrared spectroscopy (fNIRS): Are the measurements reliable?

Functional near-infrared spectroscopy (fNIRS) is a silent, non-invasive neuroimaging technique that is potentially well suited to auditory research. However, the reliability of auditory-evoked activation measured using fNIRS is largely unknown. The present study investigated the test-retest reliability of speech-evoked fNIRS responses in normally-hearing adults. Seventeen participants underwent fNIRS imaging in two sessions separated by three months. In a block design, participants were presented with auditory speech, visual speech (silent speechreading), and audiovisual speech conditions. Optode arrays were placed bilaterally over the temporal lobes, targeting auditory brain regions. A range of established metrics was used to quantify the reproducibility of cortical activation patterns, as well as the amplitude and time course of the haemodynamic response within predefined regions of interest. The use of a signal processing algorithm designed to reduce the influence of systemic physiological signals was found to be crucial to achieving reliable detection of significant activation at the group level. For auditory speech (with or without visual cues), reliability was good to excellent at the group level, but highly variable among individuals. Temporal-lobe activation in response to visual speech was less reliable, especially in the right hemisphere. Consistent with previous reports, fNIRS reliability was improved by averaging across a small number of channels overlying a cortical region of interest. Overall, the present results confirm that fNIRS can measure speech-evoked auditory responses in adults that are highly reliable at the group level, and indicate that signal processing to reduce physiological noise may substantially improve the reliability of fNIRS measurements.

Analytical approach to the temporal changes in NIRS signals to separate hemodynamic change from brain activity

In brain function measurements by near-infrared spectroscopy (NIRS), we focus on the temporal changes in the oxygenated and deoxygenated hemoglobin concentrations and propose an analytical approach to the temporal changes of the hemoglobin concentrations' cross-correlation coefficient in the brain functional signals. The cross-correlation coefficient between the oxygenated and deoxygenated hemoglobin concentrations shows negative values for brain activity and positive values for hemodynamic changes. Experiments with a 16-channel functional NIRS system show that our proposed approach clarifies the interpretation of the measured NIRS signals and it can be used to estimate the influence of hemodynamic change on brain activity.

Cortical Signal Analysis and Advances in Functional Near-Infrared Spectroscopy Signal: A Review

Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging modality that measures the concentration changes of oxy-hemoglobin (HbO) and de-oxy hemoglobin (HbR) at the same time. It is an emerging cortical imaging modality with a good temporal resolution that is acceptable for brain-computer interface applications. Researchers have developed several methods in last two decades to extract the neuronal activation related waveform from the observed fNIRS time series. But still there is no standard method for analysis of fNIRS data. This article presents a brief review of existing methodologies to model and analyze the activation signal. The purpose of this review article is to give a general overview of variety of existing methodologies to extract useful information from measured fNIRS data including pre-processing steps, effects of differential path length factor (DPF), variations and attributes of hemodynamic response function (HRF), extraction of evoked response, removal of physiological noises, instrumentation, and environmental noises and resting/activation state functional connectivity. Finally, the challenges in the analysis of fNIRS signal are summarized.

Temporal Cortex Activation to Audiovisual Speech in Normal-Hearing and Cochlear Implant Users Measured with Functional Near-Infrared Spectroscopy

BACKGROUND

Speech understanding may rely not only on auditory, but also on visual information. Non-invasive functional neuroimaging techniques can expose the neural processes underlying the integration of multisensory processes required for speech understanding in humans. Nevertheless, noise (from functional MRI, fMRI) limits the usefulness in auditory experiments, and electromagnetic artifacts caused by electronic implants worn by subjects can severely distort the scans (EEG, fMRI). Therefore, we assessed audio-visual activation of temporal cortex with a silent, optical neuroimaging technique: functional near-infrared spectroscopy (fNIRS).

METHODS

We studied temporal cortical activation as represented by concentration changes of oxy- and deoxy-hemoglobin in four, easy-to-apply fNIRS optical channels of 33 normal-hearing adult subjects and five post-lingually deaf cochlear implant (CI) users in response to supra-threshold unisensory auditory and visual, as well as to congruent auditory-visual speech stimuli.

RESULTS

Activation effects were not visible from single fNIRS channels. However, by discounting physiological noise through reference channel subtraction (RCS), auditory, visual and audiovisual (AV) speech stimuli evoked concentration changes for all sensory modalities in both cohorts (p < 0.001). Auditory stimulation evoked larger concentration changes than visual stimuli (p < 0.001). A saturation effect was observed for the AV condition.

CONCLUSIONS

Physiological, systemic noise can be removed from fNIRS signals by RCS. The observed multisensory enhancement of an auditory cortical channel can be plausibly described by a simple addition of the auditory and visual signals with saturation.

Separation of the global and local components in functional near-infrared spectroscopy signals using principal component spatial filtering

Global systemic effects not specific to a task can be prominent in functional near-infrared spectroscopy (fNIRS) signals and the separation of task-specific fNIRS signals and global nonspecific effects is challenging due to waveform correlations. We describe a principal component spatial filter algorithm for separation of the global and local effects. The effectiveness of the approach is demonstrated using fNIRS signals acquired during a right finger-thumb tapping task where the response patterns are well established. Both the temporal waveforms and the spatial pattern consistencies between oxyhemoglobin and deoxyhemoglobin signals are significantly improved, consistent with the basic physiological basis of fNIRS signals and the expected pattern of activity associated with the task.