Task-related Hemodynamic Responses Research Articles

Cortical cognitive processing during reading captured using functional-near infrared spectroscopy

Neuroimaging studies using functional magnetic resonance imaging (fMRI) have provided unparalleled insights into the fundamental neural mechanisms underlying human cognitive processing, such as high-level linguistic processes during reading. Here, we build upon this prior work to capture sentence reading comprehension outside the MRI scanner using functional near infra-red spectroscopy (fNIRS) in a large sample of participants (n = 82). We observed increased task-related hemodynamic responses in prefrontal and temporal cortical regions during sentence-level reading relative to the control condition (a list of non-words), replicating prior fMRI work on cortical recruitment associated with high-level linguistic processing during reading comprehension. These results lay the groundwork towards developing adaptive systems to support novice readers and language learners by targeting the underlying cognitive processes. This work also contributes to bridging the gap between laboratory findings and more real-world applications in the realm of cognitive neuroscience.

Hierarchical Bayesian modeling of the relationship between task-related hemodynamic responses and cortical excitability.

Investigating the relationship between task-related hemodynamic responses and cortical excitability is challenging because it requires simultaneous measurement of hemodynamic responses while applying noninvasive brain stimulation. Moreover, cortical excitability and task-related hemodynamic responses are both associated with inter-/intra-subject variability. To reliably assess such a relationship, we applied hierarchical Bayesian modeling. This study involved 16 healthy subjects who underwent simultaneous Paired Associative Stimulation (PAS10, PAS25, Sham) while monitoring brain activity using functional Near-Infrared Spectroscopy (fNIRS), targeting the primary motor cortex (M1). Cortical excitability was measured by Motor Evoked Potentials (MEPs), and the motor task-related hemodynamic responses were measured using fNIRS 3D reconstructions. We constructed three models to investigate: (1) PAS effects on the M1 excitability, (2) PAS effects on fNIRS hemodynamic responses to a finger tapping task, and (3) the correlation between PAS effects on M1 excitability and PAS effects on task-related hemodynamic responses. Significant increase in cortical excitability was found following PAS25, whereas a small reduction of the cortical excitability was shown after PAS10 and a subtle increase occurred after sham. Both HbO and HbR absolute amplitudes increased after PAS25 and decreased after PAS10. The probability of the positive correlation between modulation of cortical excitability and hemodynamic activity was 0.77 for HbO and 0.79 for HbR. We demonstrated that PAS stimulation modulates task-related cortical hemodynamic responses in addition to M1 excitability. Moreover, the positive correlation between PAS modulations of excitability and hemodynamics brought insight into understanding the fundamental properties of cortical function and cortical excitability.

Investigation of functional near-infrared spectroscopy signal quality and development of the hemodynamic phase correlation signal.

.Significance: There is a longstanding recommendation within the field of fNIRS to use oxygenated () and deoxygenated (HHb) hemoglobin when analyzing and interpreting results. Despite this, many fNIRS studies do focus on only. Previous work has shown that on its own is susceptible to systemic interference and results may mostly reflect that rather than functional activation. Studies using both and HHb to draw their conclusions do so with varying methods and can lead to discrepancies between studies. The combination of and HHb has been recommended as a method to utilize both signals in analysis.Aim: We present the development of the hemodynamic phase correlation (HPC) signal to combine and HHb as recommended to utilize both signals in the analysis. We use synthetic and experimental data to evaluate how the HPC and current signals used for fNIRS analysis compare.Approach: About 18 synthetic datasets were formed using resting-state fNIRS data acquired from 16 channels over the frontal lobe. To simulate fNIRS data for a block-design task, we superimposed a synthetic task-related hemodynamic response to the resting state data. This data was used to develop an HPC-general linear model (GLM) framework. Experiments were conducted to investigate the performance of each signal at different SNR and to investigate the effect of false positives on the data. Performance was based on each signal’s mean -value across channels. Experimental data recorded from 128 participants across 134 channels during a finger-tapping task were used to investigate the performance of multiple signals [, HHb, HbT, HbD, correlation-based signal improvement (CBSI), and HPC] on real data. Signal performance was evaluated on its ability to localize activation to a specific region of interest.Results: Results from varying the SNR show that the HPC signal has the highest performance for high SNRs. The CBSI performed the best for medium-low SNR. The next analysis evaluated how false positives affect the signals. The analyses evaluating the effect of false positives showed that the HPC and CBSI signals reflect the effect of false positives on and HHb. The analysis of real experimental data revealed that the HPC and HHb signals provide localization to the primary motor cortex with the highest accuracy.Conclusions: We developed a new hemodynamic signal (HPC) with the potential to overcome the current limitations of using and HHb separately. Our results suggest that the HPC signal provides comparable accuracy to HHb to localize functional activation while at the same time being more robust against false positives.

Task-related hemodynamic responses in human early visual cortex are modulated by task difficulty and behavioral performance.

Early visual cortex exhibits widespread hemodynamic responses in the absence of visual stimulation, which are entrained to the timing of a task and not predicted by local spiking or local field potential. Such task-related responses (TRRs) covary with reward magnitude and physiological signatures of arousal. It is unknown, however, if TRRs change on a trial-to-trial basis according to behavioral performance and task difficulty. If so, this would suggest that TRRs reflect arousal on a trial-to-trial timescale and covary with critical task and behavioral variables. We measured functional magnetic resonance imaging blood-oxygen-level-dependent (fMRI-BOLD) responses in the early visual cortex of human observers performing an orientation discrimination task consisting of separate easy and hard runs of trials. Stimuli were presented in a small portion of one hemifield, but the fMRI response was measured in the ipsilateral hemisphere, far from the stimulus representation and focus of spatial attention. TRRs scaled in amplitude with task difficulty, behavioral accuracy, reaction time, and lapses across trials. These modulations were not explained by the influence of respiration, cardiac activity, or head movement on the fMRI signal. Similar modulations with task difficulty and behavior were observed in pupil size. These results suggest that TRRs reflect arousal and behavior on the timescale of individual trials.

Laterality of prefrontal hemodynamic response measured by functional near-infrared spectroscopy before and after repetitive transcranial magnetic stimulation: A potential biomarker of clinical outcome

The factors associated with the clinical outcomes of repetitive transcranial magnetic stimulation (rTMS) in patients with major depressive disorder (MDD) remain largely unexplored. Therefore, this study aimed to examine whether rTMS can change the functional laterality of the prefrontal hemodynamic response and whether baseline functional laterality can predict the clinical outcomes of rTMS using functional near-infrared spectroscopy (fNIRS). We included 19 patients with MDD who were treated with high-frequency rTMS. The verbal fluency task was used as the activation task. We calculated the laterality index (LI) based on the task-related oxygenation response in the frontal region. First, the LI was compared before and after rTMS treatment. Second, the reduction in the Montgomery–Åsberg Depression Rating Scale (MADRS) score was compared between the rightward dominance group (pre-LI < 0) and the leftward dominance group (pre-LI ≥ 0). The findings showed a significant change in the LI after rTMS treatment. The rightward dominance group had a significantly greater reduction in MADRS score than the leftward dominance group. Subsequently, the laterality of the task-related hemodynamic response of the prefrontal region shifted leftward following left high-frequency rTMS treatment. Thus, the pre-LI calculated using fNIRS data is a possible predictor of rTMS outcomes in patients with MDD.

Task-Related Hemodynamic Response Alterations During Slacklining: An fNIRS Study in Advanced Slackliners.

The ability to maintain balance is based on various processes of motor control in complex neural networks of subcortical and cortical brain structures. However, knowledge on brain processing during the execution of whole-body balance tasks is still limited. In the present study, we investigated brain activity during slacklining, a task with a high demand on balance capabilities, which is frequently used as supplementary training in various sports disciplines as well as for lower extremity prevention and rehabilitation purposes in clinical settings. We assessed hemodynamic response alterations in sensorimotor brain areas using functional near-infrared spectroscopy (fNIRS) during standing (ST) and walking (WA) on a slackline in 16 advanced slackliners. We expected to observe task-related differences between both conditions as well as associations between cortical activity and slacklining experience. While our results revealed hemodynamic response alterations in sensorimotor brain regions such as primary motor cortex (M1), premotor cortex (PMC), and supplementary motor cortex (SMA) during both conditions, we did not observe differential effects between ST and WA nor associations between cortical activity and slacklining experience. In summary, these findings provide novel insights into brain processing during a whole-body balance task and its relation to balance expertise. As maintaining balance is considered an important prerequisite in daily life and crucial in the context of prevention and rehabilitation, future studies should extend these findings by quantifying brain processing during task execution on a whole-brain level.

Working Memory-Related Prefrontal Hemodynamic Responses in University Students: A Correlation Study of Subjective Well-Being and Lifestyle Habits.

Identification of social risk factors and the promotion of stress coping mechanisms and mental resilience are topics of interest in the field of mental health. The relationships between risk- or tolerability-associated factors and task-related hemodynamic responses in the prefrontal cortex (PFC) in adolescents may have important implications for mental health challenges. The purpose of this study was to investigate the relationship between task-related PFC hemodynamic activities and subjective well-being or lifestyle habits using wearable near-infrared spectroscopy (NIRS). In this study, after sample refinement to reduce heterogeneity, 20 university students were included in verbal working memory (VWM) task analyses and 21 were included in spatial working memory (SWM) task analyses. The task-related hemodynamic responses were detected using wearable NIRS. To assess the risk- or tolerability-associated factors, the levels of positive and negative affect were assessed using the Subjective Well-Being Inventory (SUBI) and lifestyle habits (such as gaming) were evaluated using a nine-item questionnaire. There was a positive correlation between SUBI positive affect and VWM task-related oxy-hemoglobin signal changes in the right dorsolateral PFC (DLPFC), underlining the significance of subjective well-being as an important independent emotional domain and suggesting the possibility of the differential objective evaluations of subjective well-being in the right PFC. Negative correlations between PFC activities during both VWM and SWM tasks at the left DLPFC and the number of game playing days in 1 week were also statistically significant, suggesting the presence of modality-non-specific hemodynamic regulation by habitual game playing. Each correlation was still robust after the elimination of major confounding impacts. Although further replication studies are warranted to confirm these preliminary results, this investigation of the relationship between task-related PFC hemodynamic activities and emotional domains or lifestyle habits might have clinical significance with regard to primary prevention of mental health issues in university students. To our knowledge, this is the first demonstration of these relationships with the use of wearable NIRS, which enables measurement under near natural conditions and is easy to use in schools or workplaces.

Task-related hemodynamic responses are modulated by reward and task engagement.

Hemodynamic recordings from visual cortex contain powerful endogenous task-related responses that may reflect task-related arousal, or “task engagement” distinct from attention. We tested this hypothesis with hemodynamic measurements (intrinsic-signal optical imaging) from monkey primary visual cortex (V1) while the animals’ engagement in a periodic fixation task over several hours was varied through reward size and as animals took breaks. With higher rewards, animals appeared more task-engaged; task-related responses were more temporally precise at the task period (approximately 10–20 seconds) and modestly stronger. The 2–5 minute blocks of high-reward trials led to ramp-like decreases in mean local blood volume; these reversed with ramp-like increases during low reward. The blood volume increased even more sharply when the animal shut his eyes and disengaged completely from the task (5–10 minutes). We propose a mechanism that controls vascular tone, likely along with local neural responses in a manner that reflects task engagement over the full range of timescales tested.

A widespread task-related hemodynamic response in human V1 is modulated by task difficulty

A widespread task-related hemodynamic response in human V1 is modulated by task difficulty

Performance enhancement of a brain-computer interface using high-density multi-distance NIRS

This study investigated the effectiveness of using a high-density multi-distance source-detector (SD) separations in near-infrared spectroscopy (NIRS), for enhancing the performance of a functional NIRS (fNIRS)-based brain-computer interface (BCI). The NIRS system that was used for the experiment was capable of measuring signals from four SD separations: 15, 21.2, 30, and 33.5 mm, and this allowed the measurement of hemodynamic response alterations at various depths. Fifteen participants were asked to perform mental arithmetic and word chain tasks, to induce task-related hemodynamic response variations, or they were asked to stay relaxed to acquire a baseline signal. To evaluate the degree of BCI performance enhancement by high-density channel configuration, the classification accuracy obtained using a typical low-density lattice SD arrangement, was compared to that obtained using the high-density SD arrangement, while maintaining the SD separation at 30 mm. The analysis results demonstrated that the use of a high-density channel configuration did not result in a noticeable enhancement of classification accuracy. However, the combination of hemodynamic variations, measured by two multi-distance SD separations, resulted in the significant enhancement of overall classification accuracy. The results of this study indicated that the use of high-density multi-distance SD separations can likely provide a new method for enhancing the performance of an fNIRS-BCI.

Simultaneously estimating the task-related and stimulus-evoked components of hemodynamic imaging measurements.

Task-related hemodynamic responses contribute prominently to functional magnetic resonance imaging (fMRI) recordings. They reflect behaviorally important brain states, such as arousal and attention, and can dominate stimulus-evoked responses, yet they remain poorly understood. To help characterize these responses, we present a method for parametrically estimating both stimulus-evoked and task-related components of hemodynamic responses from subjects engaged in temporally predictable tasks. The stimulus-evoked component is modeled by convolving a hemodynamic response function (HRF) kernel with spiking. The task-related component is modeled by convolving a Fourier-series task-related function (TRF) kernel with task timing. We fit this model with simultaneous electrode recordings and intrinsic-signal optical imaging from the primary visual cortex of alert, task-engaged monkeys. With high [Formula: see text], the model returns HRFs that are consistent across experiments and recording sites for a given animal and TRFs that entrain to task timing independent of stimulation or local spiking. When the task schedule conflicts with that of stimulation, the TRF remains locked to the task emphasizing its behavioral origins. The current approach is strikingly more robust to fluctuations than earlier ones and gives consistently, if modestly, better fits. This approach could help parse the distinct components of fMRI recordings made in the context of a task.

A machine learning approach to identify functional biomarkers in human prefrontal cortex for individuals with traumatic brain injury using functional near-infrared spectroscopy.

BackgroundWe have explored the potential prefrontal hemodynamic biomarkers to characterize subjects with Traumatic Brain Injury (TBI) by employing the multivariate machine learning approach and introducing a novel task‐related hemodynamic response detection followed by a heuristic search for optimum set of hemodynamic features. To achieve this goal, the hemodynamic response from a group of 31 healthy controls and 30 chronic TBI subjects were recorded as they performed a complexity task.MethodsTo determine the optimum hemodynamic features, we considered 11 features and their combinations in characterizing TBI subjects. We investigated the significance of the features by utilizing a machine learning classification algorithm to score all the possible combinations of features according to their predictive power.Results and ConclusionsThe identified optimum feature elements resulted in classification accuracy, sensitivity, and specificity of 85%, 85%, and 84%, respectively. Classification improvement was achieved for TBI subject classification through feature combination. It signified the major advantage of the multivariate analysis over the commonly used univariate analysis suggesting that the features that are individually irrelevant in characterizing the data may become relevant when used in combination. We also conducted a spatio‐temporal classification to identify regions within the prefrontal cortex (PFC) that contribute in distinguishing between TBI and healthy subjects. As expected, Brodmann areas (BA) 10 within the PFC were isolated as the region that healthy subjects (unlike subjects with TBI), showed major hemodynamic activity in response to the High Complexity task. Overall, our results indicate that identified temporal and spatio‐temporal features from PFC's hemodynamic activity are promising biomarkers in classifying subjects with TBI.

Inconvenient correlation – RT–BOLD relationship for homogeneous and fast reactions

Reaction time (RT), a widely used measure of human performance in experimental psychology, has recently been included as a regressor of interest in functional magnetic resonance imaging (fMRI) data analysis. Few studies reported RT-related brain regions, but the nature of this activity is not fully understood. We aimed at exploring this topic by implementing a simple saccadic task which evokes fast and homogeneous reactions that require only the basic neural processes. Thus, a spatial cueing paradigm was chosen and implemented in a simultaneous fMRI and eye-tracking experiment. As a result, we found a wide set of brain regions showing trial-by-trial correlations of blood-oxygenation-level-dependent (BOLD) signal with saccadic RT. These regions included medial and lateral frontal lobes, bilateral intraparietal sulci, anterior insular cortices as well as the right thalamus and medial visual cortex. Further analysis was conducted in order to verify quantitatively the impact of a “time on task” effect on task-related hemodynamic responses (HDRs). The results provide evidence that even a small difference in RTs can be linked with significant increase of HDR in task-related areas. Moreover, this increase is not linear, but rather quadratic. Our findings highlight the importance of controlling for RT in fMRI data analysis when contrasting conditions that vary in RT to avoid the misinterpretation of results.

Evaluative processing of ambivalent stimuli in patients with schizophrenia and depression: A [15O] H2O PET study

Decision making in an emotionally conflicting situation is important in social life. We aimed to address the similarity and disparity of neural correlates involved in processing ambivalent stimuli in patients with schizophrenia and patients with depression. Behavioral task-related hemodynamic responses were measured using [15O]H2O positron emission tomography (PET) in 12 patients with schizophrenia and 12 patients with depression. The task was a modified word-stem completion task, which was designed to evoke ambivalence in forced and non-forced choice conditions. The prefrontal cortex and the cerebellum were found to show increased activity in the healthy control group. In the schizophrenia group, activity in these two regions was negligible. In the depression group, the pattern of activity was altered and a functional compensatory recruitment of the inferior parietal regions was suggested. The prefrontal cortex seems to be associated with the cognitive control to resolve the conflict toward the ambivalent stimuli, whereas the cerebellum reflects the sustained working memory to search for compromise alternatives. The deficit of cerebellar activation in the schizophrenia group might underlie the inability to search and consider compromising responses for conflict resolution.

Likelihood-Based Hypothesis Tests for Brain Activation Detection From MRI Data Disturbed by Colored Noise: A Simulation Study

Functional magnetic resonance imaging (fMRI) data that are corrupted by temporally colored noise are generally preprocessed (i.e., prewhitened or precolored) prior to functional activation detection. In this paper, we propose likelihood-based hypothesis tests that account for colored noise directly within the framework of functional activation detection. Three likelihood-based tests are proposed: the generalized likelihood ratio (GLR) test, the Wald test, and the Rao test. The fMRI time series is modeled as a linear regression model, where one regressor describes the task-related hemodynamic response, one regressor accounts for a constant baseline and one regressor describes potential drift. The temporal correlation structure of the noise is modeled as an autoregressive (AR) model. The order of the AR model is determined from practical null data sets using Akaike's information criterion (with penalty factor 3) as order selection criterion. The tests proposed are based on exact expressions for the likelihood function of the data. Using Monte Carlo simulation experiments, the performance of the proposed tests is evaluated in terms of detection rate and false alarm rate properties and compared to the current general linear model (GLM) test, which estimates the coloring of the noise in a separate step. Results show that theoretical asymptotic distributions of the GLM, GLR, and Wald test statistics cannot be reliably used for computing thresholds for activation detection from finite length time series. Furthermore, it is shown that, for a fixed false alarm rate, the detection rate of the proposed GLR test statistic is slightly, but (statistically) significantly improved compared to that of the common GLM-based tests. Finally, simulations results reveal that all tests considered show seriously inferior performance if the order of the AR model is not chosen sufficiently high to give an adequate description of the correlation structure of the noise, whereas the effects of (slightly) overmodeling are observed to be less harmful.