Transcranial Doppler ultrasonography monitoring of cerebral hemodynamics during performance of cognitive tasks: a review

Statistical Complexity Analysis of Neurovascular Coupling with Cognitive Stimulation in Healthy Participants

Neurovascular coupling (NVC) is the tight relationship between changes in cerebral blood flow and neural activation. NVC can be evaluated non-invasively using transcranial Doppler ultrasound (TCD)-measured changes in brain activation (cerebral blood velocity [CBv]) using different cognitive tasks and stimuli. This study used a novel approach to analyzing CBv changes occurring in response to 20 tasks from the Addenbrooke's Cognitive Examination III in 40 healthy individuals. The novel approach compared various information entropy families (permutation, Tsallis, and Rényi entropy) and statistical complexity measures based on disequilibrium. Using this approach, we found the majority of the attention, visuospatial, and memory tasks from the Addenbrooke's Cognitive Examination III that showed lower statistical complexity values when compared with the resting state. On the entropy-complexity (HC) plane, a receiver operating characteristic curve was used to distinguish between baseline and cognitive tasks using the area under the curve. Best area under the curve values were 0.91 ± 0.04, p = .001, to distinguish between resting and cognitively active states. Our findings show that brain hemodynamic signals captured with TCD can be used to distinguish between resting state (baseline) and cognitive effort (stimulation paradigms) using entropy and statistical complexity as an alternative method to traditional techniques such as coherent averaging of CBv signals. Further work should directly compare these analysis methods to identify the optimal method for analyzing TCD-measured changes in NVC.

The effect of CO2 on the age dependence of neurovascular coupling

Prior studies have identified variable effects of aging on neurovascular coupling (NVC). Carbon dioxide (CO2) affects both cerebral blood velocity (CBv) and NVC, but the effects of age on NVC under different CO2 conditions are unknown. Therefore, we investigated the effects of aging on NVC in different CO2 states during cognitive paradigms. Seventy-eight participants (18-78 yr), with well-controlled comorbidities, underwent continuous recordings of CBv by bilateral insonation of middle (MCA) and posterior (PCA) cerebral arteries (transcranial Doppler), blood pressure, end-tidal CO2, and heart rate during poikilocapnia, hypercapnia (5% CO2 inhalation), and hypocapnia (paced hyperventilation). Neuroactivation via visuospatial (VS) and attention tasks (AT) was used to stimulate NVC. Peak percentage and absolute change in MCAv/PCAv, were compared between CO2 conditions and age groups (≤30, 31-60, and >60 yr). For the VS task, in poikilocapnia, younger adults had a lower NVC response compared with older adults [mean difference (MD): -7.92% (standard deviation (SD): 2.37), P = 0.004], but comparable between younger and middle-aged groups. In hypercapnia, both younger [MD: -4.75% (SD: 1.56), P = 0.009] and middle [MD: -4.58% (SD: 1.69), P = 0.023] age groups had lower NVC responses compared with older adults. Finally, in hypocapnia, both older [MD: 5.92% (SD: 2.21), P = 0.025] and middle [MD: 5.44% (SD: 2.27), P = 0.049] age groups had greater NVC responses, compared with younger adults. In conclusion, the magnitude of NVC response suppression from baseline during hyper- and hypocapnia, did not differ significantly between age groups. However, the middle age group demonstrated a different NVC response while under hypercapnic conditions, compared with hypocapnia.NEW & NOTEWORTHY This study describes the effects of age on neurovascular coupling under altered CO2 conditions. We demonstrated that both hypercapnia and hypocapnia suppress neurovascular coupling (NVC) responses. Furthermore, that middle age exhibits an NVC response comparable with younger adults under hypercapnia, and older adults under hypocapnia.

Depression of dynamic cerebral autoregulation during neural activation: The role of responders and non-responders

Neurovascular coupling (NVC) interaction with dynamic cerebral autoregulation (dCA) remains unclear. We investigated the effect of task complexity and duration on the interaction with dCA. Sixteen healthy participants (31.6 ± 11.6 years) performed verbal fluency (naming-words (NW)) and serial subtraction (SS) paradigms, of varying complexity, at durations of 05, 30 and 60 s. The autoregulation index (ARI), was estimated from the bilateral middle cerebral artery blood velocity (MCAv) step response, calculated by transfer function analysis (TFA), for each paradigm during unstimulated (2 min) and neuroactivated (1 min) segments. Intraclass correlation (ICC) and coefficient of variation (CV) determined reproducibility for two visits and objective criteria were applied to classify responders (R) and non-responders (NoR) to task-induced MCAv increase. ICC values demonstrated fair reproducibility in all tasks. ARI decreased in right (RH) and left (LH) hemispheres, irrespective of paradigm complexity and duration (p < 0.0001). Bilateral ARI estimates were significantly decreased during NW for the R group only (p < 0.0001) but were reduced in both R (p < 0.0001) and NoR (p = 0.03) groups for SS tasks compared with baseline. The reproducible attenuation of dCA efficiency due to paradigm-induced NVC response, its interaction, and different behaviour in R and NoR, warrant further research in different physiological and clinical conditions.

Evaluating the influence of altered cerebral hemodynamics on cognitive performance in asymptomatic carotid artery stenosis: A systematic review

OBJECTIVE

Substantial controversy exists regarding asymptomatic carotid stenosis (ACS) and its potential role in the pathophysiology of cognitive impairment. If proven, this hypothesis may suggest an additional definition for symptomatic carotid disease that would alter current management. This study aimed to synthesize the literature evaluating the relationship between impaired cerebral hemodynamics and cognition in patients with ACS.

METHODS

A literature search was performed using MEDLINE, Embase, and EBM Reviews through May 2022. We included prospective case-control studies that used validated, objective measure(s) of either global cognition or one or more domains of cognitive function and assessed cerebrovascular reserve (CVR).

RESULTS

Five studies were included, comprising a total of 782 patients with moderate (50%-69%) to severe (70%-99%) ACS. Patients with ACS and impaired ipsilateral CVR demonstrated significant cognitive impairment compared with controls. Patients with unilateral or bilateral ACS and normal CVR had cognitive scores similar to controls. Those with bilateral CVR impairment demonstrated the lowest cognitive scores.

CONCLUSIONS

This review lends support to the claim that cognitive impairment, likely the result of impaired cerebral hemodynamics, is an under-recognized morbidity in patients with ACS. CVR may serve as an additional tool to determine whether patients are in fact symptomatic from their carotid stenosis and warrant consideration for intervention.

The Clinical Relevance of Autonomic Dysfunction, Cerebral Hemodynamics, and Sleep Interactions in Individuals Living With SCI

A myriad of physiological impairments is seen in individuals after a spinal cord injury (SCI). These include altered autonomic function, cerebral hemodynamics, and sleep. These physiological systems are interconnected and likely insidiously interact leading to secondary complications. These impairments negatively influence quality of life. A comprehensive review of these systems, and their interplay, may improve clinical treatment and the rehabilitation plan of individuals living with SCI. Thus, these physiological measures should receive more clinical consideration. This special communication introduces the under investigated autonomic dysfunction, cerebral hemodynamics, and sleep disorders in people with SCI to stakeholders involved in SCI rehabilitation. We also discuss the linkage between autonomic dysfunction, cerebral hemodynamics, and sleep disorders and some secondary outcomes are discussed. Recent evidence is synthesized to make clinical recommendations on the assessment and potential management of important autonomic, cerebral hemodynamics, and sleep-related dysfunction in people with SCI. Finally, a few recommendations for clinicians and researchers are provided.

Association of accelerometer-measured physical activity intensity, sedentary time, and exercise time with incident Parkinson's disease

Evidence regarding the association between physical activity and Parkinson's disease (PD) risk is generally limited due to the use of self-report questionnaires. We aimed to quantify the separate and combined effects of accelerometer-measured light physical activity (LPA), moderate-to-vigorous physical activity (MVPA), sedentary time and exercise timing with incident PD. 96,422 participants without prior PD and with usable accelerometer data were included from UK Biobank. Time spent in sedentary activity, LPA, MVPA, and exercise timing were estimated using machine learning models. The study outcome was incident PD. Over a median follow-up duration of 6.8 years, 313 participants developed PD. There was a L-shaped association for LPA and MVPA, and a reversed L-shaped association for sedentary time, with the risk of incident PD (all P for nonlinearity < 0.001). Similar trends were found across three time-windows (morning, midday-afternoon, and evening). Compared with those with both low LPA (<3.89 h/day) and low MVPA (<0.27 h/day), the adjusted HR (95% CI) of PD risk was 0.49 (0.36-0.66), 0.19 (0.36-0.66) and 0.13 (0.09-0.18), respectively, for participants with high MVPA only, high LPA only, and both high LPA and high MVPA. Moreover, participants with both low LPA and high sedentary time (≥9.41 h/day) (adjusted HR, 5.59; 95% CI: 4.10-7.61), and those with both low MVPA and high sedentary time (adjusted HR, 3.93; 95% CI: 2.82-5.49) had the highest risk of incident PD. In conclusion, regardless of exercise timing (morning, midday-afternoon, and evening), there was an inverse association for accelerometer-measured MVPA and LPA, and a positive association for sedentary time, with incident PD.

Performance, Hemodynamics, and Stress in a Two-Day Vigilance Task: Practical and Theoretical Implications

OBJECTIVE

To explore vigilance task performance, cerebral blood flow velocity (CBFV), workload, and stress in a within-subjects, two-session experiment.

BACKGROUND

Vigilance, or sustained attention, tasks are often characterized by a decline in operator performance and CBFV with time on task, and high workload and stress. Though performance is known to improve with practice, past research has not included measures of CBFV, stress, and workload in a within-subjects multi-session design, which may also provide insight into ongoing theoretical debate.

METHOD

Participants performed a vigilance task on two separate occasions. Performance, CBFV, workload, and self-reported stress were measured.

RESULTS

Within each session, results were consistent with the vigilance profile found in prior research. Across sessions, performance improved but the time on task decrement remained. Mean CBFV and workload ratings did not differ between sessions, but participants reported significantly less distress, worry, and engagement after session two compared to one.

CONCLUSION

Though practice may not disrupt the standard vigilance profile, it may serve to improve overall performance and reduce stress. However, repeated exposure may have negative implications for engagement and mind-wandering.

APPLICATION

It is important to better understand the relationship between experience, performance, physiological response, and self-reported stress and workload in vigilance because real-world environments often require operators to do the same task over many occasions. While performance improvement and reduced distress is an encouraging result, the decline in engagement requires further research. Results across sessions fail to provide support to the mind-wandering theory of vigilance.

Challenging neurovascular coupling through complex and variable duration cognitive paradigms: A subcomponent analysis

A similar pattern of cerebral blood velocity (CBv) response has been observed for neurovascular coupling (NVC) assessment with cognitive tasks of varying complexity and duration. This lack of specificity could result from parallel changes in arterial blood pressure (BP) and PaCO₂, which could confound the estimates of NVC integrity. Healthy participants (n = 16) underwent recordings at rest (5 min sitting) and during randomized paradigms of different complexity (naming words (NW) beginning with P-, R-, V- words and serial subtractions (SS) of 100-2, 100-7, 1000-17, with durations of 5, 30 and 60 s). Bilateral CBv (middle cerebral arteries, transcranial Doppler), end-tidal CO₂ (EtCO₂, capnography), blood pressure (BP, Finapres) and heart rate (HR, ECG) were recorded continuously. The bilateral CBv response to all paradigms was classified under objective criteria to select only responders, then the repeated data were averaged between visits. Bilateral CBv change to tasks was decomposed into the relative contributions (subcomponents) of arterial BP (V_BP; neurogenic), critical closing pressure (V_CrCP; metabolic) and resistance area product (V_RAP; myogenic). A temporal effect was demonstrated in bilateral V_BP and V_RAP during all tasks (p<0.002), increased V_BP early (between 0 and 10 s) and followed by decreases of V_RAP late (25-35 s) in the response. V_CrCP varied by complexity and duration (p<0.046). The main contributions to CBv responses to cognitive tasks of different complexity and duration were V_BP and V_RAP, whilst a smaller contribution from V_CrCP would suggest sensitivity to metabolic demands. Further studies are needed to assess the influence of different paradigms, ageing and cerebrovascular conditions.

Neurovascular coupling on trial: How the number of trials completed impacts the accuracy and precision of temporally derived neurovascular coupling estimates

Standard practices for quantifying neurovascular coupling (NVC) with transcranial Doppler ultrasound (TCD) require participants to complete one-to-ten repetitive trials. However, limited empirical evidence exists regarding how the number of trials completed influences the validity and reliability of temporally derived NVC metrics. Secondary analyses was performed on 60 young healthy participants (30 females/30 males) who completed eight cyclical eyes-closed (20-seconds), eyes-open (40-seconds) NVC trials, using the "Where's Waldo?" visual paradigm. TCD data was obtained in posterior and middle cerebral arteries (PCA and MCA, respectively). The within-day (n = 11) and between-day (n = 17) reliability were assessed at seven- and three-time points, respectively. Repeat testing from the reliability aims were also used for the concurrent validity analysis (n = 160). PCA metrics (i.e., baseline, peak, percent increase, and area-under-the-curve) demonstrated five trials produced excellent intraclass correlation coefficient (ICC) 95% confidence intervals for validity and within-day reliability (>0.900), whereas between-day reliability was good-to-excellent (>0.750). Likewise, 95% confidence intervals for coefficient of variation (CoV) measures ranged from acceptable (<20%) to excellent (<5%) with five-or-more trials. Employing fewer than five trials produced poor/unacceptable ICC and CoV metrics. Future NVC, TCD-based research should therefore have participants complete a minimum of five trials when quantifying the NVC response with TCD via a "Where's Waldo?" paradigm.

The scalability of common paradigms for assessment of cognitive function: A functional transcranial Doppler study

Cognitive paradigms induce changes in cerebral blood flow (CBF) associated with increased metabolic demand, namely neurovascular coupling (NVC). We tested the hypothesis that the effect of complexity and duration of cognitive paradigms will either enhance or inhibit the NVC response. Bilateral CBF velocity (CBFV) in the middle cerebral arteries (MCAs) via transcranial Doppler ultrasound (TCD), blood pressure (BP), electrocardiogram (ECG) and end-tidal CO₂ (EtCO₂) of 16 healthy participants (aged 21–71 years) were simultaneously recorded at rest and during randomized paradigms of different complexities (naming words beginning with P-,R-,V- words and serial subtractions of 100–2,100–7,1000–17), and durations (5s, 30s and 60s). CBFV responses were population mean normalized from a 30-s baseline period prior to task initiation. A significant increase in bilateral CBFV response was observed at the start of all paradigms and provided a similar pattern in most responses, irrespective of complexity or duration. Although significant inter-hemispherical differences were found during performance of R-word and all serial subtraction paradigms, no lateralisation was observed in more complex naming word tasks. Also, the effect of duration was manifested at late stages of 100–7, but not for other paradigms. CBFV responses could not distinguish different levels of complexity or duration with a single presentation of the cognitive paradigm. Further studies of the ordinal scalability of the NVC response are needed with more advanced modelling techniques, or different types of neural stimulation.

Principal component analysis to identify the major contributors to task-activated neurovascular responses

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A range of metrics are available to measure to cerebrovascular responses to task activation.

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We used principal component analysis to reduce dimensionality in a large dataset and determine physiological variables with the greatest contribution to the cerebrovascular response.

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Peak percentage change in cerebrovascular response was a consistent marker across datasets and the visuospatial task contributed the most variance.

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There was limited overlap between cognitive tasks and domains suggesting lack of redundancy in the data.

Background

Consensus on the optimal metrics for neurovascular coupling (NVC) is lacking. The aim of this study was to use principal component analysis (PCA) to determine the most significant contributors to NVC responses in healthy adults (HC), Alzheimer's disease (AD), and mild cognitive impairment (MCI).

New method

PCA was applied to three datasets: 1) 69 HC, 2) 30 older HC, 34 AD, and 22 MCI, 3) 1&2 combined. Data were extracted on peak percentage change in cerebral blood flow velocity (CBFv), variance ratio (VR), cross-correlation function peak (CCF), and blood pressure, for five cognitive tasks. An equamax rotation was applied and factors were significant where the eignevalue was ≥1. Rotated factor loadings ≥0.4 determined significant NVC variables.

Results

PCA identified 12 significant factors accounting for 78% of variance (all datasets). Contributing variables loaded differently on the factors across the datasets. In datasets 1&2, peak percentage change in CBFv contributed to factors explaining the most variance (45–58%), whereas cognitive test scores, fluency and memory domains contributed the least (15–37%). In the combined dataset, CBFv, CCF and fluency domain contributed the majority (33–43%), whereas VR and attention the least (6–24%).

Conclusions

Peak percentage change in CBFv and the visuospatial task consistently accounted for a large proportion of the variance, suggesting these are robust NVC markers for future studies.

Functional transcranial Doppler: Selection of methods for statistical analysis and representation of changes in flow velocity

INTRODUCTION

Transcranial Doppler (TCD) is a method used to study cerebral hemodynamics. In the majority of TCD studies, regression analysis and analysis of variance are the most frequently applied statistical methods. However, due to the dynamic and interdependent nature of flow velocity, nonparametric tests may allow for better statistical analysis and representation of results.

METHOD

The sample comprised 30 healthy participants, aged 33.87 ± 7.48 years; with 33% (n = 10) females. During a visuo-motor task, the mean flow velocity (MFV) in the middle cerebral artery (MCA) was measured using TCD. The MFV was converted to values relative to the resting state. The results obtained were analyzed using the general linear model (GLM) and the general additional model (GAM). The fit indices of both analysis methods were compared with each other.

RESULTS

Both MCAs showed a steady increase in MFV during the visuo-motor task, smoothly returning to resting state values. During the first 20 seconds of the visuo-motor task, the MFV increased by a factor of 1.06 ± 0.07 in the right-MCA and by a factor of 1.08 ± 0.07 in the left-MCA. GLM and GAM showed a statistically significant change in MFV (GLM:F(2, 3598) = 16.76, P < .001; GAM:F(2, 3598) = 21.63, P < .001); together with effects of hemispheric side and gender (GLM:F(4, 3596) = 7.83, P < .005; GAM:F(4, 3596) = 2.13, P = .001). Comparing the models using the χ2 test for goodness of fit yields a significant difference χ2 (9.9556) = 0.6836, P < .001.

CONCLUSIONS

Both the GLM and GAM yielded valid statistical models of MFV in the MCA in healthy subjects. However, the model using the GAM resulted in improved fit indices. The GAM's advantage becomes even clearer when the MFV curves are visualized; yielding a more realistic approach to brain hemodynamics, thus allowing for an improvement in the interpretation of the mathematical and statistical results. Our results demonstrate the utility of the GAM for the analysis and representation of hemodynamic parameters.

Association between sedentary time and cognitive function: A focus on different domains of sedentary behavior

Studies which examined the association between sedentary behavior (SB) and cognitive function have presented equivocal findings. Mentally active/inactive sedentary domains may relate differently to cognitive function. We examined associations between SB and cognitive function, specifically focusing on different domains. Participants were recruited from the Nijmegen Exercise Study 2018 in the Netherlands. SB (h/day) was measured with the Sedentary Behavior Questionnaire. Cognitive function was assessed with a validated computer self-test (COST-A), and a z-score calculated for global cognitive function. Multivariate linear regression assessed associations between tertiles of sedentary time and cognitive function. Cognition tests were available from 2821 participants, complete data from 2237 participants (43% female), with a median age of 61 [IQR 52-67] and a mean sedentary time of 8.3 ± 3.2 h/day. In fully adjusted models, cognitive function was significantly better in participants with the highest total sedentary time (0.07 [95% CI 0.02-0.12], P = 0.01), work-related sedentary time (0.13 [95% CI 0.07-0.19], P < 0.001), and non-occupational computer time (0.07 [95% CI 0.02-0.12], P = 0.01), compared to the least sedentary. Leisure sedentary time and time spent sedentary in the domains TV, reading or creative time showed no association with cognitive function in final models (all P > 0.05). We found a strong, independent positive association between total SB and cognitive function in a heterogenous population. This relation was not consistent across different domains, with especially work- and computer-related SB being positively associated with cognitive function. This highlights the importance of assessing the various sedentary domains in understanding the relation between sedentary time and cognitive function.

Cerebral blood flow response rate to task-activation using a novel method can discriminate cognitive impairment from healthy aging

Objective.A new method to classify individuals as 'responders' to task-activated cerebral blood flow velocity (CBFv) has recently been developed. This study investigated whether CBFv response rate to task-activation is affected by Alzheimer's disease (AD) and mild cognitive impairment (MCI).Approach.The 95th thresholds for cross correlation function peak and variance ratio were derived from 270 unstimulated, healthy hemispheres, and were used to classify the presence of a response to task-activation. Thresholds were applied to five cognitive tasks (attention, verbal fluency, language, visuospatial, memory) in CBFv data from 30 healthy older adults (HC), 35 AD and 22 MCI participants. Cumulative response rate (CRR) was calculated from the sum of responses across five tasks, for both hemispheres. Area under the curve (AUC) was derived from receiver operating characteristic (ROC) curve analysis.Main results. The number of responders differed significantly between tasks (p < 0.005) and diagnostic groups (p = 0.011). On post hoc tests there were more responders in the visuospatial (79%-90%) compared to fluency (45%-80%), language (50%-77%), and memory (44%-70%) tasks bilaterally, and responders were greater in the HC (70%) compared to AD (41%) and MCI (23%) groups to at least eight out of ten tasks. At an optimal threshold of 7.5 out of 10 responses, the AUC-ROC distinguished HC from AD and MCI with a; sensitivity 66% and specificity 70% (AUC = 0.72).Significance. Using a novel method to classify responders to cognitive task-activation, HC demonstrated a higher CRR than those with MCI or AD, and a threshold of <8 responses distinguished healthy ageing from dementia.

Testing the Darwinian function of lateralization. Does separation of workload between brain hemispheres increase cognitive performance?

Brain lateralization is a fundamental aspect of the organization of brain and behavior in the animal kingdom, begging the question about its Darwinian function. We tested the possibility that lateralization enhances cognitive performance in single- and dual-tasks. Previous studies reported mixed results on this topic and only a handful of studies have measured functional brain lateralization and performance independently and simultaneously. We therefore examined a possible positive effect of the strength and direction of lateralization on two demanding cognitive tasks: A visuospatial task (mental rotation MR), and a language task (word generation WG), executed either as a singletask or as dual-task. Participants (n = 72) performed these tasks while their single-task brain lateralization was assessed with functional Transcranial Doppler for both tasks. From these measurements we determined strength and direction of lateralization for both tasks and the individual pattern of lateralization (contralateral or ipsilateral) was derived. These factors, along with sex, were used in a GLM analysis to determine if they predicted the respective performance measure of the tasks. We found that for MR there was a significant medium effect of direction of lateralization on performance with better performance in left-lateralized (atypical) participants (partial eta squared 0.061; p = .039). After correction for outliers, there was a significant effect for strength (p = .049). For the dual-task, there was a significant positive medium effect of strength of lateralization on performance (partial eta squared 0.062; p = .038, respectively) No other association between direction or strength in either tests were found. We conclude that there is no evidence for hemispheric crowding, and that strength of lateralization may be a factor that contributes to the evolutionary selection of functional brain lateralization. Pattern of lateralization does not, explaining the large inter-individual variation in these traits.

Vascular and haemodynamic issues of brain ageing

The population is ageing worldwide, thus increasing the burden of common age-related disorders to the individual, society and economy. Cerebrovascular diseases (stroke, dementia) contribute a significant proportion of this burden and are associated with high morbidity and mortality. Thus, understanding and promoting healthy vascular brain ageing are becoming an increasing priority for healthcare systems. In this review, we consider the effects of normal ageing on two major physiological processes responsible for vascular brain function: Cerebral autoregulation (CA) and neurovascular coupling (NVC). CA is the process by which the brain regulates cerebral blood flow (CBF) and protects against falls and surges in cerebral perfusion pressure, which risk hypoxic brain injury and pressure damage, respectively. In contrast, NVC is the process by which CBF is matched to cerebral metabolic activity, ensuring adequate local oxygenation and nutrient delivery for increased neuronal activity. Healthy ageing is associated with a number of key physiological adaptations in these processes to mitigate age-related functional and structural declines. Through multiple different paradigms assessing CA in healthy younger and older humans, generating conflicting findings, carbon dioxide studies in CA have provided the greatest understanding of intrinsic vascular anatomical factors that may mediate healthy ageing responses. In NVC, studies have found mixed results, with reduced, equivalent and increased activation of vascular responses to cognitive stimulation. In summary, vascular and haemodynamic changes occur in response to ageing and are important in distinguishing “normal” ageing from disease states and may help to develop effective therapeutic strategies to promote healthy brain ageing.

Psychopathological Symptom Load and Distinguishable Cerebral Blood Flow Velocity Patterns in Patients With Schizophrenia and Healthy Controls: A Functional Transcranial Doppler Study

Introduction: Schizophrenia is a severe psychiatric disorder, with executive dysfunction and impaired processing speed playing a pivotal role in the course of the disease. In patients with schizophrenia, neurocognitive deficits appear to be related to alterations in cerebral hemodynamics. It is not fully understood if psychopathological symptom load (i.e., presence and severity of symptoms) is also related to alterations in cerebral hemodynamics. We aim to study the relationship between psychopathological symptom load and cerebral hemodynamics in the Middle Cerebral Artery (MCA) during a cognitive task in patients with schizophrenia and healthy controls. Methodology: Cerebral hemodynamics in the MCA were examined in 30 patients with schizophrenia and 15 healthy controls using functional Transcranial Doppler (fTCD) during the Trail Making Test (TMT). Psychopathological symptoms were measured using the Brief Psychiatric Rating Scale (BPRS). Patients were dichotomized according to BPRS scores: mild-moderate (BPRS < 41, n = 15) or marked-severe (BPRS ≧ 41, n = 15). Mean blood flow velocity (MFV) in the MCA and processing speed of the TMT were analyzed. Cerebral hemodynamics were analyzed using the general additional model (GAM) with a covariate analysis of variance (ANCOVA) for group comparisons. Results: Patients and healthy controls were comparable regarding demographics. Patients had a slower processing speed for the TMT-A (patients-severe: 52s, patients-moderate: 40s, healthy-controls: 32s, p = 0.019) and TMT-B [patients-severe: 111s, patients-moderate: 76s, healthy-controls: 66s, p < 0.001)]. Patients demonstrated differing hemodynamic profiles in both TMTs: TMT- A [F _{(6, 1,792)} = 17, p < 0.000); TMT-B [F _{(6, 2,692)} = 61.93, p < 0.000], with a delay in increase in MFV and a failure to return to baseline values. Conclusions: Patients with schizophrenia demonstrated slower speeds of processing during both the TMT-A and TMT-B. The speed of processing deteriorated with increasing psychopathological symptom load, additionally a distinct cerebral hemodynamic pattern in the MCA was observed. Our results further support the view that severity of schizophrenia, particularly psychopathological symptom load, influences performance in neurocognitive tasks and is related to distinct patterns of brain hemodynamics.

A probabilistic approach for calibration time reduction in hybrid EEG-fTCD brain-computer interfaces

Background

Generally, brain–computer interfaces (BCIs) require calibration before usage to ensure efficient performance. Therefore, each BCI user has to attend a certain number of calibration sessions to be able to use the system. However, such calibration requirements may be difficult to fulfill especially for patients with disabilities. In this paper, we introduce a probabilistic transfer learning approach to reduce the calibration requirements of our EEG–fTCD hybrid BCI designed using motor imagery (MI) and flickering mental rotation (MR)/word generation (WG) paradigms. The proposed approach identifies the top similar datasets from previous BCI users to a small training dataset collected from a current BCI user and uses these datasets to augment the training data of the current BCI user. To achieve such an aim, EEG and fTCD feature vectors of each trial were projected into scalar scores using support vector machines. EEG and fTCD class conditional distributions were learnt separately using the scores of each class. Bhattacharyya distance was used to identify similarities between class conditional distributions obtained using training trials of the current BCI user and those obtained using trials of previous users.

Results

Experimental results showed that the performance obtained using the proposed transfer learning approach outperforms the performance obtained without transfer learning for both MI and flickering MR/WG paradigms. In particular, it was found that the calibration requirements can be reduced by at least 60.43% for the MI paradigm, while at most a reduction of 17.31% can be achieved for the MR/WG paradigm.

Conclusions

Data collected using the MI paradigm show better generalization across subjects.

The Effects of Healthy Ageing on Cerebral Blood Flow Responses to Cognitive Testing

Background: Transcranial Doppler Ultrasonography (TCD) can be utilised to measure the tight coupling of cerebral blood flow velocity (CBFv) in response to cognitive demand by task activation, termed neurovascular coupling.

Aims: To investigate the differences in neurovascular coupling between healthy older (>50 years) and younger (18-49 years) adults in response to cognitive testing.

Methods: Fifty-four older (n=25) and younger (n=29) adults underwent continuous bilateral TCD, beat-to-beat blood pressure (MAP; Finapres), heart rate (HR; electrocardiogram), and end-tidal CO₂ (ETCO₂; capnography) monitoring. After a 5-min baseline period, memory (M1-4: recalling three learned words, learning a name and address, recalling US presidents and UK prime ministers, and recalling the previously learned name and address) and visuospatial (V1-4: drawing a cube and infinity diagram, drawing a clock face, counting dots, and recognising obscured letters) tasks from the Addenbrooke's Cognitive Examination (ACE-III) were performed. Data are mean (standard deviation).

Results: In the memory paradigms, the peak percentage change in CBFv differed significantly between younger and older groups only in the dominant hemisphere during the M1 task, (2.17 (9.16)% vs. 8.38 (9.27)%, respectively, p=0.017). In the visuospatial paradigm, there were also significant differences in peak percentage change in CBFv between younger and older groups in the V1 (5.87 (8.32)% vs. 11.89 (6.60)%, p=0.005) and V2 tasks (6.30 (8.72)% vs. 11.30 (7.77)%, p=0.032).

Conclusion: Healthy older adults demonstrate augmented cerebrovascular physiology in response to cognitive challenge compared to younger adults. The impact of abnormal ageing on cerebrovascular physiology, for example, related to cognitively impaired states, requires further investigation.

Brain Connectivity Analysis Under Semantic Vigilance and Enhanced Mental States

In this paper, we present a method to quantify the coupling between brain regions under vigilance and enhanced mental states by utilizing partial directed coherence (PDC) and graph theory analysis (GTA). The vigilance state is induced using a modified version of stroop color-word task (SCWT) while the enhancement state is based on audio stimulation with a pure tone of 250 Hz. The audio stimulation was presented to the right and left ears simultaneously for one-hour while participants perform the SCWT. The quantification of mental states was performed by means of statistical analysis of indexes based on GTA, behavioral responses of time-on-task (TOT), and Brunel Mood Scale (BRMUS). The results show that PDC is very sensitive to vigilance decrement and shows that the brain connectivity network is significantly reduced with increasing TOT, p < 0.05. Meanwhile, during the enhanced state, the connectivity network maintains high connectivity as time passes and shows significant improvements compared to vigilance state. The audio stimulation enhances the connectivity network over the frontal and parietal regions and the right hemisphere. The increase in the connectivity network correlates with individual differences in the magnitude of the vigilance enhancement assessed by response time to stimuli. Our results provide evidence for enhancement of cognitive processing efficiency with audio stimulation. The BRMUS was used to evaluate the emotional states of vigilance task before and after using the audio stimulation. BRMUS factors, such as fatigue, depression, and anger, significantly decrease in the enhancement group compared to vigilance group. On the other hand, happy and calmness factors increased with audio stimulation, p < 0.05.

An Examination of Compensatory Effort in a Vigilance Task Using Transcranial Doppler Sonography

This study uses a novel neuroergonomic approach to determine whether blood flow to the frontal cortex is sensitive to task demands and indicative of compensatory effort regulation that may occur in response to the vigilance decrement. The present study used transcranial Doppler sonography (TCD) to examine the anterior cerebral artery (ACA) and its response to different demands of a vigilance task over time. Participants completed a vigilance task in a slow or fast event rate condition. The results demonstrated a vigilance decrement in both conditions and that workload was higher when the event rate was faster. However, blood flow velocity in the ACA did not change as a function of time, nor was it sensitive to the event rate manipulation. While previous research has shown that TCD is a useful neuroergonomic tool for vigilance monitoring, current results indicate that TCD monitoring of the ACA may not be worthwhile.

Predictors of cognitive functioning after carotid revascularization

PURPOSE

High-grade carotid stenosis can affect cognition, but the relationship between stenosis correction and cognitive outcome is not fully understood, yet. The aim of this study was to evaluate the predictors of post-operative neurocognitive functioning in patients with symptomatic severe internal carotid artery (ICA) stenosis undergoing carotid endarterectomy (CEA).

MATERIALS AND METHODS

Patients with history of transient ischemic attack within the past 6 months and ipsilateral high-grade stenosis of ICA undergoing CEA were prospectively enrolled. Cerebral hemodynamics was assessed by means of the cerebral vasomotor reactivity (CVR) to hypercapnia measured through transcranial Doppler ultrasonography. Coloured Progressive Matrices plus Complex Figure Copy Test, and phonemic plus categorical (ca) Verbal Fluency tests were performed to assess right and left hemisphere cognitive functions, respectively. Cerebral hemodynamics and cognitive functions were assessed before and 6 months after CEA.

RESULTS

One hundred and eighty-one patients were included. The mean age was 73.2 (6.9) years and 121 (66.9%) were males. At 6 months from CEA, the scores obtained in the cognitive tests exploring the re-vascularized hemisphere's functions and ipsilateral cerebral hemodynamics were improved. At multivariate linear regression analysis, the 6-month change in cognitive performance was inversely associated with age [ß = -0.17, 95% confidence interval (CI) -0.22 to -0.12; p < .001] and CVR value obtained before CEA on the side of ICA stenosis (ß = -6.25, 95% CI -7.40 to -5.10; p < .001).

CONCLUSIONS

In patients with symptomatic high-grade ICA stenosis, age and cerebral hemodynamic status before CEA predicted the neurocognitive performance changes after surgical stenosis correction.

Sensor Networks for Aerospace Human-Machine Systems

Intelligent automation and trusted autonomy are being introduced in aerospace cyber-physical systems to support diverse tasks including data processing, decision-making, information sharing and mission execution. Due to the increasing level of integration/collaboration between humans and automation in these tasks, the operational performance of closed-loop human-machine systems can be enhanced when the machine monitors the operator's cognitive states and adapts to them in order to maximise the effectiveness of the Human-Machine Interfaces and Interactions (HMI²). Technological developments have led to neurophysiological observations becoming a reliable methodology to evaluate the human operator's states using a variety of wearable and remote sensors. The adoption of sensor networks can be seen as an evolution of this approach, as there are notable advantages if these sensors collect and exchange data in real-time, while their operation is controlled remotely and synchronised. This paper discusses recent advances in sensor networks for aerospace cyber-physical systems, focusing on Cognitive HMI² (CHMI²) implementations. The key neurophysiological measurements used in this context and their relationship with the operator's cognitive states are discussed. Suitable data analysis techniques based on machine learning and statistical inference are also presented, as these techniques allow processing both neurophysiological and operational data to obtain accurate cognitive state estimations. Lastly, to support the development of sensor networks for CHMI² applications, the paper addresses the performance characterisation of various state-of-the-art sensors and the propagation of measurement uncertainties through a machine learning-based inference engine. Results show that a proper sensor selection and integration can support the implementation of effective human-machine systems for various challenging aerospace applications, including Air Traffic Management (ATM), commercial airliner Single-Pilot Operations (SIPO), one-to-many Unmanned Aircraft Systems (UAS), and space operations management.

Associations of transcranial doppler velocity, age, and gender with cognitive function in children with sickle cell anemia in Nigeria

Children with sickle cell anemia (SCA) have elevated cerebral blood velocity relative to healthy peers. The primary aim of this study was to evaluate the association between cerebral blood velocity, measured by transcranial Doppler (TCD) ultrasound, age, and gender with cognitive function in children with SCA in Nigeria. Eighty-three children (Mage = 9.10, SD = 1.90 years; 55% female) with SCA in Nigeria completed cognitive assessments and a TCD ultrasound. The association between TCD velocity and measures of perceptual reasoning (Raven's Progressive Matrices), working memory (WISC-IV Digit Span), and executive planning (Tower of London, TOL) were assessed. Results showed that elevated TCD velocity significantly predicted lower scores on TOL Time Violations and Total Problem-Solving Time when controlling for BMI, hemoglobin level, and parent education, suggesting that TCD velocity is related to the efficiency of executive function. Further, age was negatively related to children's performance on the Ravens Matrices and TOL Total Correct, and boys showed greater deficits on the TOL Total Correct relative to girls. Moderation analyses for gender showed that there was a conditional negative association between TCD velocity and Digit Span for boys, but not for girls. Findings suggest that children with SCA in Nigeria with elevated TCD velocity are at risk for deficits in efficiency of executive planning, and boys with elevated TCD velocity are particularly at increased risk for deficits in auditory working memory. Implications of this study are important for interventions to reduce cerebral blood velocity and the use of TCD in this population.

Effects of brain training on brain blood flow (The Cognition and Flow Study-CogFlowS): protocol for a feasibility randomised controlled trial of cognitive training in dementia

INTRODUCTION

Cognitive training is an emerging non-pharmacological treatment to improve cognitive and physical function in mild cognitive impairment (MCI) and early Alzheimer's disease (AD). Abnormal brain blood flow is a key process in the development of cognitive decline. However, no studies have explored the effects of cognitive training on brain blood flow in dementia. The primary aim of this study is to assess the feasibility for a large-scale, randomised controlled trial of cognitive training in healthy older adults (HC), MCI and early AD.

METHODS AND ANALYSIS

This study will recruit 60 participants, in three subgroups of 20 (MCI, HC, AD), from primary, secondary and community services. Participants will be randomised to a 12-week computerised cognitive training programme (five × 30 min sessions per week), or waiting-list control. Participants will undergo baseline and follow-up assessments of: mood, cognition, quality of life and activities of daily living. Cerebral blood flow will be measured at rest and during task activation (pretraining and post-training) by bilateral transcranial Doppler ultrasonography, alongside heart rate (3-lead ECG), end-tidal CO2 (capnography) and beat-to-beat blood pressure (Finometer). Participants will be offered to join a focus group or semistructured interview to explore barriers and facilitators to cognitive training in patients with dementia. Qualitative data will be analysed using framework analysis, and data will be integrated using mixed methods matrices.

ETHICS AND DISSEMINATION

Bradford Leeds Research Ethics committee awarded a favourable opinion (18/YH/0396). Results of the study will be published in peer-reviewed journals, and presented at national and international conferences on ageing and dementia.

TRIALS REGISTRATION NUMBER

NCT03656107; Pre-results.

EEG-fTCD hybrid brain-computer interface using template matching and wavelet decomposition

OBJECTIVE

We aim at developing a hybrid brain-computer interface that utilizes electroencephalography (EEG) and functional transcranial Doppler (fTCD). In this hybrid BCI, EEG and fTCD are used simultaneously to measure electrical brain activity and cerebral blood velocity respectively in response to flickering mental rotation (MR) and word generation (WG) tasks. In this paper, we improve both the accuracy and information transfer rate (ITR) of this novel hybrid brain computer interface (BCI) we designed in our previous work.

APPROACH

To achieve such aim, we extended our feature extraction approach through using template matching and multi-scale analysis to extract EEG and fTCD features, respectively. In particular, template matching was used to analyze EEG data whereas 5-level wavelet decomposition was applied to fTCD data. Significant EEG and fTCD features were selected using Wilcoxon signed rank test. Support vector machines classifier (SVM) was used to project EEG and fTCD selected features of each trial into scalar SVM scores. Moreover, instead of concatenating EEG and fTCD feature vectors corresponding to each trial, we proposed a Bayesian fusion approach of EEG and fTCD evidences.

MAIN RESULTS

Average accuracy and average ITR of 98.11% and 21.29 bits min^-1 were achieved for WG versus MR classification while MR versus baseline yielded 86.27% average accuracy and 8.95 bit min^-1 average ITR. In addition, average accuracy of 85.29% and average ITR of 8.34 bits min^-1 were obtained for WG versus baseline.

SIGNIFICANCE

The proposed analysis techniques significantly improved the hybrid BCI performance. Specifically, for MR/WG versus baseline problems, we achieved twice of the ITRs obtained in our previous study. Moreover, the ITR of WG versus MR problem is 4-times the ITR we obtained before for the same problem. The current analysis methods boosted the performance of our EEG-fTCD BCI such that it outperformed the existing EEG-fNIRS BCIs in comparison.

Hemispheric language lateralization in presurgical patients with temporal lobe epilepsy: Improving the retest reliability of functional transcranial Doppler sonography

Since its introduction, functional transcranial Doppler sonography (fTCD) has been extensively applied in research and clinical settings and has now become part of the routine presurgical work-up of patients with epilepsy. Because of its importance in planning neurosurgical interventions and predicting possible cognitive risks, the reproducibility of fTCD in determining hemispheric language lateralization (HLL) has to be ensured. In the present study, fTCD was performed twice in 33 initially lateralized patients with temporal lobe epilepsy (TLE) as part of their presurgical work-up, using a standard word generation paradigm. Initially, the standard analysis, including only the statistical examination of fTCD data, was applied, and a rather poor retest reliability of r = 0.41 was obtained (p = 0.017). Because of doubts concerning appropriate task performance in some patients, subsequently, a two-step data analysis was introduced, including an additional qualitative evaluation of fTCD data regarding (1) instruction-compliant task performance, (2) sufficient quality of the baseline phase, and (3) adequate increase in cerebral blood flow velocity (CBFV) during the activation phase. Attributable to a more valid interpretation of fTCD data after the application of the qualitative step, the reproducibility of HLL significantly improved (p = 0.007) to a high retest reliability of r = 0.84 (p < 0.000). In clinical settings, psychological and situational factors seem to strongly influence the reproducibility of fTCD determining HLL. Accordingly, we highly recommend the complementation of the standard statistical examination of fTCD data by an additional qualitative evaluation (two-step data analysis), as this extra security is particularly desirable because of its direct implications for the further evaluation of neurosurgical interventions. This article is part of the Special Issue "Individualized Epilepsy Management: Medicines, Surgery and Beyond".

A novel motor imagery hybrid brain computer interface using EEG and functional transcranial Doppler ultrasound

BACKGROUND

Hybrid brain computer interfaces (BCIs) combining multiple brain imaging modalities have been proposed recently to boost the performance of single modality BCIs.

NEW METHOD

In this paper, we propose a novel motor imagery (MI) hybrid BCI that uses electrical brain activity recorded using Electroencephalography (EEG) as well as cerebral blood flow velocity measured using functional transcranial Doppler ultrasound (fTCD). Features derived from the power spectrum for both EEG and fTCD signals were calculated. Mutual information and linear support vector machines (SVM) were employed for feature selection and classification.

RESULTS

Using the EEG-fTCD combination, average accuracies of 88.33%, 89.48%, and 82.38% were achieved for right arm MI versus baseline, left arm MI versus baseline, and right arm MI versus left arm MI respectively. Compared to performance measures obtained using EEG only, the hybrid system provided significant improvement in terms of accuracy by 4.48%, 5.36%, and 4.76% respectively. In addition, average transmission rates of 4.17, 5.45, and 10.57 bits/min were achieved for right arm MI versus baseline, left arm MI versus baseline, and right arm MI versus left arm MI respectively.

COMPARISON WITH EXISTING METHODS

Compared to EEG-fNIRS hybrid BCIs in literature, we achieved similar or higher accuracies with shorter task duration.

CONCLUSIONS

The proposed hybrid system is a promising candidate for real-time BCI applications.

The Assessment of Cerebrovascular Response to a Language Task from the Addenbrooke's Cognitive Examination in Cognitive Impairment: A Feasibility Functional Transcranial Doppler Ultrasonography Study

Background:

The incidence of dementia is predicted to rise rapidly, but sensitive diagnostic tests remain elusive. Changes in cerebral blood flow velocity (CBFv) can occur at an early stage of cognitive decline, and can be measured by transcranial Doppler ultrasonography (TCD).

Objective:

The aim of this study was to characterize the CBFv changes that occur in healthy older adults (HC), mild cognitive impairment (MCI), and Alzheimer’s disease (AD), in response to a language task from the Addenbrooke’s cognitive examination (ACE-III).

Methods:

Participants underwent bilateral TCD, continuous heart rate (ECG), end-tidal CO₂ (capnography, ETCO₂), and beat-to-beat blood pressure (Finometer, MAP), monitoring, during a 5-minute baseline, followed by cognitive tasks from the ACE-III. Data are presented for a language task (repeating words and phrases aloud), as peak percentage change in CBFv, HR, MAP, and ETCO₂ from a normalized baseline.

Results:

30 participants (mean age 73.2 years, 20% female) were recruited; HC (n = 10), MCI (n = 10), AD (n = 10). Language scores did not differ between groups (p = 0.16). Peak percentage change in CBFv differed between groups with the language task (HC: 15.9 (7.5)%, MCI: 6.7 (4.5)%, AD: 0.1 (7.1)%; p < 0.005). However, changes in MAP (HC: 7.9 (4.6)%, MCI: –0.1 (0.9)%, AD: 0.9 (4.4)%; p < 0.005), HR (HC: 8.8 (8.2)%, MCI: 0.7 (4.3)%, AD: –0.5 (5.6)%; p = 0.005), and ETCO₂ (HC: –0.9 (3.2)%, MCI: 0.9 (3.2)%, AD: –5.2 (5.7)%; p = 0.006), also occurred.

Conclusions:

TCD measured CBFv changes to a language task from the ACE-III was feasible in a cognitively impaired population, further work is required in a larger population.

Towards optimal visual presentation design for hybrid EEG-fTCD brain-computer interfaces

OBJECTIVE

In this paper, we introduce a novel hybrid brain-computer interface (BCI) system that measures electrical brain activity as well as cerebral blood velocity using electroencephalography (EEG) and functional transcranial Doppler ultrasound (fTCD) respectively in response to flickering mental rotation (MR) and flickering word generation (WG) cognitive tasks as well as a fixation cross that represents the baseline. This work extends our previous approach, in which we showed that motor imagery induces simultaneous changes in EEG and fTCD to enable task discrimination; and hence, provides a design approach for a hybrid BCI. Here, we show that instead of using motor imagery, the proposed visual stimulation technique enables the design of an EEG-fTCD based BCI with higher accuracy.

APPROACH

Features based on the power spectrum of EEG and fTCD signals were calculated. Mutual information and support vector machines were used for feature selection and classification purposes.

MAIN RESULTS

EEG-fTCD combination outperformed EEG by 4.05% accuracy for MR versus baseline problem and by 5.81% accuracy for WG versus baseline problem. An average accuracy of 92.38% was achieved for MR versus WG problem using the hybrid combination. Average transmission rates of 4.39, 3.92, and 5.60 bits min^-1 were obtained for MR versus baseline, WG versus baseline, and MR versus WG problems respectively.

SIGNIFICANCE

In terms of accuracy, the current visual presentation outperforms the motor imagery visual presentation we designed before for the EEG-fTCD system by 10% accuracy for task versus task problem. Moreover, the proposed system outperforms the state of the art hybrid EEG-fNIRS BCIs in terms of accuracy and/or information transfer rate. Even though there are still limitations of the proposed system, such promising results show that the proposed hybrid system is a feasible candidate for real-time BCIs.

Design and Validation of an FPGA-Based Configurable Transcranial Doppler Neurofeedback System for Chronic Pain Patients

Neurofeedback is a self-regulation technique that can be applied to learn to voluntarily control cerebral activity in specific brain regions. In this work, a Transcranial Doppler-based configurable neurofeedback system is proposed and described. The hardware configuration is based on the Red Pitaya board, which gives great flexibility and processing power to the system. The parameter to be trained can be selected between several temporal, spectral, or complexity features from the cerebral blood flow velocity signal in different vessels. As previous studies have found alterations in these parameters in chronic pain patients, the system could be applied to help them to voluntarily control these parameters. Two protocols based on different temporal lengths of the training periods have been proposed and tested with six healthy subjects that were randomly assigned to one of the protocols at the beginning of the procedure. For the purposes of the testing, the trained parameter was the mean cerebral blood flow velocity in the aggregated data from the two anterior cerebral arteries. Results show that, using the proposed neurofeedback system, the two groups of healthy volunteers can learn to self-regulate a parameter from their brain activity in a reduced number of training sessions.

Neurovascular coupling response to cognitive examination in healthy controls: a multivariate analysis

Cognitive testing with transcranial Doppler ultrasonography (TCD) has been used to assess neurovascular coupling (NVC), but few studies address its multiple contributions. Subcomponent analysis considers the relative myogenic (resistance area product, RAP) and metabolic (critical closing pressure (CrCP)) contributors. The aim of this study was to investigate the changes in subcomponents that occur with cognitive stimulation with the Addenbrooke's Cognitive Examination (ACE-III) in healthy controls. Healthy volunteers underwent continuous recording of bilateral TCD, heart rate (HR, three-lead ECG), end-tidal CO2 (ETCO2 , capnography), and mean arterial pressure (MAP, Finometer). The study comprised a 5-min baseline recording, followed by all 20 paradigms from the ACE-III. The cerebral blood flow velocity (CBFv) response was decomposed into the relative contributions (subcomponents); VBP (MAP), VCrCP (CrCP), and VRAP (RAP). Data are presented as peak population normalized mean changes from baseline, and median area under the curve (AUC). Forty bilateral datasets were obtained (27 female, 37 right hand dominant). VBP increased at task initiation in all paradigms but differed between tasks (range (SD): 4.06 (8.92)-16.04 (12.23) %, P < 0.05). HR, but not ETCO2 , also differed significantly (P < 0.05). Changes in VRAP reflected changes in MAP, but in some paradigms atypical responses were seen. VCrCP AUC varied significantly within paradigm sections (range [SD]: 18.4 [24.17] to 244.21 [243.21] %*s, P < 0.05). All paradigms demonstrated changes in subcomponents with cognitive stimulation, and can be ranked based on their relative presumed metabolic demand. The integrity of NVC requires further investigation in patient populations.

Measurement of neurovascular coupling in human motor cortex using simultaneous transcranial Doppler and electroencephalography

OBJECTIVE

Event-related desynchronization (ERD) is a relative power decrease of electroencephalogram (EEG) signals in a specific frequency band during physical motor execution, while transcranial Doppler (TCD) measures cerebral blood flow velocity. The objective of this study was to investigate the neurovascular coupling in the motor cortex by using an integrated EEG and TCD system, and to find any difference in hemodynamic responses in healthy young male and female adults.

APPROACH

Thirty healthy volunteers, aged 20-30 years, were recruited for this study. The subjects were asked to perform a motor task for the duration of a provided visual cue. Simultaneous EEG and TCD recording was carried out using a new integrated system to detect the ERD arising from the EEG signals, and to measure the mean blood flow velocity of the left and right middle cerebral arteries from bilateral TCD signals.

MAIN RESULTS

The results showed a significant decrease in EEG power in the mu band (7.5-12.5 Hz) during the motor task compared to the resting phase. It showed significant increase in desynchronization on the contralateral side of the motor task compared to the ipsilateral side. Mean blood flow velocity during the task phase was significantly higher in comparison with the resting phase at the contralateral side. The results also showed a significantly higher increase in the percentage of mean blood flow velocity in the contralateral side of motor task compared to the ipsilateral side. However, no significant difference in desynchronization or change of mean blood flow velocity was found between males and females.

SIGNIFICANCE

A combined TCD-EEG system successfully detects ERD and blood flow velocity in cerebral arteries, and can be used as a useful tool to study neurovascular coupling in the brain. There is no significant difference in the hemodynamic responses in healthy young males and females.

The assessment of neurovascular coupling with the Addenbrooke’s Cognitive Examination: a functional transcranial Doppler ultrasonographic study

Cerebrovascular dysfunction occurs early in dementia and can be identified by transcranial Doppler ultrasonography (TCD). Few studies have examined cerebral blood flow velocity (CBFv) responses to a detailed cognitive battery. This study aimed to characterize all CBFv responses, and the effect of hemispheric dominance, to the Addenbrooke’s Cognitive Examination (ACE-III) in healthy volunteers. Forty volunteers underwent continuous bilateral TCD, beat-to-beat blood pressure (MAP; Finapres), heart rate (HR; electrocardiogram), and end-tidal CO2 (ETCO2; capnography) monitoring. After a 5-min baseline period, all tasks from the ACE-III were performed in 3 sections (A: attention, fluency, memory; B: language; C: visuospatial, memory). Data are population mean normalized percentage (PM%) change from a 20-s baseline period before task initiation. Forty bilateral data sets were obtained (27 women, 37 right-hand dominant). All paradigms produced a sharp increase in CBFv in both dominant (PM% range: 3.29 to 9.70%) and nondominant (PM% range: 4.34 to 11.63%) hemispheres at task initiation, with associated increases in MAP (PM% range: 3.06 to 16.04%). ETCO2 did not differ significantly at task initiation (PM% range: −1.1 to 2.4%, P > 0.05). HR differed significantly across A and C tasks at initiation (PM% range: −1.1 to 2.4%, P < 0.05), but not B tasks. In conclusion, all tasks resulted in increases in CBFv, differing significantly between paradigms. These results require further investigation in a cognitively impaired population.

NEW & NOTEWORTHY This study is the first to provide a normative data set of cerebral blood flow velocity (CBFv) responses to a complete cognitive assessment (Addenbrooke’s Cognitive Examination, ACE-III) in a large sample ( n = 40) of healthy volunteers. All tasks produced peak and sustained increases in CBFv to different extents. The ACE-III is a feasible tool to assess neurovascular coupling with transcranial Doppler ultrasonography. These data can be used to inform the most appropriate cognitive task to elicit CBFv responses for future studies.

The relationship between spatial ability, cerebral blood flow and learning with dynamic images: A transcranial Doppler ultrasonography study

Determining the effect of dynamic images on learning is often limited to performance measures. This study explores the impact from the perspective of cerebral blood flow in the brain during learning. Performance and neurophysiological response in high and low spatial ability were compared during learning with dynamic images. Individuals with high spatial ability appear to be better suited to learn with complex images such as dynamic images that move in time and space. The results presented here suggest that spatial ability can help to determine the effectiveness of the media we use for teaching.

Prenatal and pubertal testosterone affect brain lateralization

After decades of research, the influence of prenatal testosterone on brain lateralization is still elusive, whereas the influence of pubertal testosterone on functional brain lateralization has not been investigated, although there is increasing evidence that testosterone affects the brain in puberty. We performed a longitudinal study, investigating the relationship between prenatal testosterone concentrations in amniotic fluid, pubertal testosterone concentrations in saliva, and brain lateralization (measured with functional Transcranial Doppler ultrasonography (fTCD)) of the Mental Rotation, Chimeric Faces and Word Generation tasks. Thirty boys and 30 girls participated in this study at the age of 15 years. For boys, we found a significant interaction effect between prenatal and pubertal testosterone on lateralization of Mental Rotation and Chimeric Faces. In the boys with low prenatal testosterone levels, pubertal testosterone was positively related to the strength of lateralization in the right hemisphere, while in the boys with high prenatal testosterone levels, pubertal testosterone was negatively related to the strength of lateralization. For Word Generation, pubertal testosterone was negatively related to the strength of lateralization in the left hemisphere in boys. For girls, we did not find any significant effects, possibly because their pubertal testosterone levels were in many cases below quantification limit. To conclude, prenatal and pubertal testosterone affect lateralization in a task-specific way. Our findings cannot be explained by simple models of prenatal testosterone affecting brain lateralization in a similar way for all tasks. We discuss alternative models involving age dependent effects of testosterone, with a role for androgen receptor distribution and efficiency.

Neurocognitive functioning and cerebrovascular reactivity after carotid endarterectomy

OBJECTIVE

To evaluate in patients with TIA and ipsilateral high-grade internal carotid artery (ICA) stenosis whether changes in cognitive performance and cerebral hemodynamics occurred after carotid endarterectomy (CEA) and to explore their relationship.

METHODS

Participants were patients who underwent CEA, had TIA within the last 6 months, and had an ipsilateral severe ICA stenosis. Coloured Progressive Matrices (CPM) plus Complex Figure Copy Test (CFCT) and phonemic (ph) plus categorical (ca) Verbal Fluency (VF) tests were performed to assess right and left hemisphere cognitive functions, respectively. Hemodynamics was assessed with transcranial Doppler ultrasonography by means of the cerebral vasomotor reactivity (CVR) to hypercapnia.

RESULTS

A total of 137 patients were included. Before CEA, patients with right ICA obtained lower scores on the CPM and CFCT; patients with left ICA stenosis performed worse on the phonemic and categorical VF tests. The CVR was decreased on the side of the stenosis. At 6 months from CEA, CVR and cognitive performance were significantly improved. The performance change in cognitive tests exploring the revascularized hemisphere was positively associated with the ipsilateral CVR variation (CPM: R² for linear regression = 0.759, _adjR² = 0.737; CFCT: R² = 0.734, _adjR² = 0.710; (ph)VF: R² = 0.774, _adjR² = 0.749; (ca)VF: R² = 0.732, _adjR² = 0.703).

CONCLUSION

Cognitive performance was enhanced at 6 months since CEA, and the improvement was related to the CVR increase. Cerebral hemodynamics may be an independent and potentially reversible determinant of cognitive dysfunction in severe carotid artery disease.

Cerebrovascular Hemodynamics in Women

Sex and gender, as biological and social factors, significantly influence health outcomes. Among the biological factors, sex differences in vascular physiology may be one specific mechanism contributing to the observed differences in clinical presentation, response to treatment, and clinical outcomes in several vascular disorders. This review focuses on the cerebrovascular bed and summarizes the existing literature on sex differences in cerebrovascular hemodynamics to highlight the knowledge deficit that exists in this domain. The available evidence is used to generate mechanistically plausible and testable hypotheses to underscore the unmet need in understanding sex-specific mechanisms as targets for more effective therapeutic and preventive strategies.

Effects of acute hypoxia on human cognitive processing: a study using ERPs and SEPs

Although hypoxia has the potential to impair the cognitive function, the effects of acute hypoxia on the high-order brain function (executive and/or inhibitory processing) and somatosensory ascending processing remain unknown. We tested the hypothesis that acute hypoxia impairs both motor executive and inhibitory processing and somatosensory ascending processing. Fifteen healthy subjects performed two sessions (sessions 1 and 2), consisting of electroencephalographic event-related potentials with somatosensory Go/No-go paradigms and somatosensory-evoked potentials (SEPs) under two conditions (hypoxia and normoxia) on different days. On 1 day, participants breathed room air in the first and second sessions of the experiment; on the other day, participants breathed room air in the first session, and 12% O₂ in the second session. Acute hypoxia reduced the peak amplitudes of Go-P300 and No-go-P300, and delayed the peak latency of Go-P300. However, no significant differences were observed in the peak amplitude or latency of N140, behavioral data, or the amplitudes and latencies of individual SEP components between the two conditions. These results suggest that acute hypoxia impaired neural activity in motor executive and inhibitory processing, and delayed higher cognitive processing for motor execution, whereas neural activity in somatosensory processing was not affected by acute hypoxia.NEW & NOTEWORTHY Hypoxia has the potential to impair the cognitive function, but the effects of acute hypoxia on the cognitive function remain debatable. We investigated the effects of acute hypoxia on human cognitive processing using electroencephalographic event-related potentials and somatosensory-evoked potentials. Acute normobaric hypoxia impaired neural activity in motor executive and inhibitory processing, but no significant differences were observed in neural activity in somatosensory processing.

Altered cerebral blood flow velocity features in fibromyalgia patients in resting-state conditions

The aim of this study is to characterize in resting-state conditions the cerebral blood flow velocity (CBFV) signals of fibromyalgia patients. The anterior and middle cerebral arteries of both hemispheres from 15 women with fibromyalgia and 15 healthy women were monitored using Transcranial Doppler (TCD) during a 5-minute eyes-closed resting period. Several signal processing methods based on time, information theory, frequency and time-frequency analyses were used in order to extract different features to characterize the CBFV signals in the different vessels. Main results indicated that, in comparison with control subjects, fibromyalgia patients showed a higher complexity of the envelope CBFV and a different distribution of the power spectral density. In addition, it has been observed that complexity and spectral features show correlations with clinical pain parameters and emotional factors. The characterization features were used in a lineal model to discriminate between fibromyalgia patients and healthy controls, providing a high accuracy. These findings indicate that CBFV signals, specifically their complexity and spectral characteristics, contain information that may be relevant for the assessment of fibromyalgia patients in resting-state conditions.

Cerebral hemodynamics during scene viewing: Hemispheric lateralization predicts temporal gaze behavior associated with distinct modes of visual processing

Systematic patterns of eye movements during scene perception suggest a functional distinction between 2 viewing modes: an ambient mode (characterized by short fixations and large saccades) thought to reflect dorsal activity involved with spatial analysis, and a focal mode (characterized by long fixations and small saccades) thought to reflect ventral activity involved with object analysis. Little neuroscientific evidence exists supporting this claim. Here, functional transcranial Doppler ultrasound (fTCD) was used to investigate whether these modes show hemispheric specialization. Participants viewed scenes for 20 s under instructions to search or memorize. Overall, early viewing was right lateralized, whereas later viewing was left lateralized. This right-to-left shift interacted with viewing task (more pronounced in the memory task). Importantly, changes in lateralization correlated with changes in eye movements. This is the first demonstration of right hemisphere bias for eye movements servicing spatial analysis and left hemisphere bias for eye movements servicing object analysis. (PsycINFO Database Record

Transcranial Doppler Sonography Reveals Reductions in Hemispheric Asymmetry in Healthy Older Adults during Vigilance

Given that older adults are remaining longer in the workforce, their ability to perform demanding cognitive tasks such as vigilance assignments needs to be thoroughly examined, especially since many vigilance assignments affect public safety (e.g., aviation, medicine and long distance driving). Previous research exploring the relation between aging and vigilance is conflicted, with some studies finding decreased vigilance performance in older adults but others finding no effect of age. We sought a better understanding of effects of age on vigilance by assessing neurophysiological change over the course of a vigil in young (aged 18–24) and healthy older (aged 66–77) adults. To measure temporal changes in cerebral blood flow, participants underwent functional transcranial doppler (fTCD) recording during a 1 h vigilance task. Based on research showing a compensatory effect of increased left hemisphere activation during vigilance in young adults and the “hemispheric asymmetry reduction in older adults” (HAROLD) model, we predicted that during vigilance our older adults would show greater left hemisphere activation but perform at a similar level compared to young adults. While cerebral blood flow velocity (CBFV) declined over time in both groups, only young adults showed the typical right-lateralized CBFV pattern. Older adults showed greater left hemisphere activation consistent with the HAROLD model. However, the increased left hemisphere activation did not appear to be compensatory as the older adults performed at a significantly lower level compared to young adults over the vigil. Findings are discussed in terms of the HAROLD model of healthy aging and the resource theory of vigilance.

Impaired cerebrovascular responsiveness and cognitive performance in adults with type 2 diabetes

AIM

Cognitive deficits in type 2 diabetes mellitus (T2DM) may be partly attributable to stiffness in cerebral arteries and impaired vasodilator function, limiting the ability to increase blood flow in brain regions to meet cognitive demands. We undertook a comparison of cerebrovascular responsiveness (CVR) and cognitive performance in adults with and without T2DM.

METHODS

Older adults with (50) and without (Herath, Cherbuin, Eramudugolla, & Anstey, 2016) T2DM underwent transcranial Doppler ultrasound measurements of basal cerebral mean blood flow velocity (MBFV) and pulsatility index (PI), a measure of arterial stiffness, in the middle cerebral arteries (MCA). A battery of tasks assessing domains of working memory, executive function and information processing/motor speed was then administered while MBFV was recorded. CVR to cognitive tasks was calculated as a percentage increase in MBFV from the basal level.

RESULTS

There was no difference in basal MBFV between groups. However, PI was 14% higher in the T2DM group (P<0.05), who performed poorer across all cognitive domains assessed and displayed poorer CVR in three tasks. Cognitive performance was inversely related to the PI/MBFV ratio, an indicator of intracranial stenosis.

DISCUSSION

Impaired cerebral perfusion during mental tasks is accompanied by poor cognitive performance and stiffness in the cerebral vessels.

The Neuroergonomics of Vigilance

OBJECTIVE

The aim of this study was to examine the effects of uncertainty about where in the field of view critical signals for detection appear during a vigilance task (spatial uncertainty) on cerebral blood flow velocity (CBFV) and oculomotor fatigue.

BACKGROUND

Neuroergonomics is a dimension of human factors founded by Raja Parasuraman that studies brain functions underlying performance at work. Neuroergonomic studies have shown that observers in vigilance tasks lose information-processing resources over time and experience oculomotor fatigue as indexed by a temporal decline in CBFV and elevation in eye closure as reflected in the PERCLOS metric. Because spatial uncertainty increases an observer's need for visual scanning relative to a spatial certainty condition, it was anticipated that spatial uncertainty would result in a greater temporal decline in CBFV and increased eye closure in a vigilance session.

METHOD

Observers performed a simulated unmanned aerial vehicle (UAV) control task wherein collision flight paths were the events to be detected. UAV images could appear at random in any one of five locations on the controller's display (spatial uncertainty) or only in a fixed location (spatial certainty).

RESULTS

Signal detection was poorer in the spatial-uncertain relative to the certain condition, and predictions regarding CBFV and eye closure were confirmed.

CONCLUSION

Vigilance tasks involving spatial uncertainty are more neurophysiologically taxing than those in which spatial uncertainty is not a factor.

APPLICATION

The neuroergonomic approach helps in understanding the effects of psychophysical factors in vigilance and to signify when performance aiding is needed.