Method For Functional Mapping Research Articles

Preoperative Cortical Mapping for Brain Tumor Surgery Using Navigated Transcranial Stimulation: Analysis of Accuracy

Transcranial magnetic stimulation (TMS) represents a distinctive technique for non-invasive brain stimulation. Recent advancements in image processing have enabled the enhancement of TMS by integrating magnetic resonance imaging (MRI) modalities with TMS via a neuronavigation system. The aim of this study is to assess the efficacy of navigated TMS for cortical mapping in comparison to surgical mapping using direct electrical stimulation (DES). This study involved 30 neurosurgical procedures for tumors located in or adjacent to the precentral gyrus. The DES points were compared with TMS responses based on the original distances of vectorial modules. There was a notable similarity in the points obtained from the two mapping methods. The distances between the geometric centers of TMS and DCS were 4.85 ± 1.89 mm. A strong correlation was identified between these vectorial points (r = 0.901, p < 0.001). The motor threshold in TMS was highest in the motor cortex adjacent to the tumor compared to the normal cortex (p < 0.001). Patients with deficits exhibited excellent accuracy in both methods. In view of this, TMS demonstrated reliable and precise application in brain mapping, which is a promising method for preoperative functional mapping in motor cortex tumor surgery.

Identification of bone mineral density associated genes with shared genetic architectures across multiple tissues: Functional insights for EPDR1, PKDCC, and SPTBN1.

Recent studies suggest a shared genetic architecture between muscle and bone, yet the underlying molecular mechanisms remain elusive. This study aims to identify the functionally annotated genes with shared genetic architecture between muscle and bone using the most up-to-date genome-wide association study (GWAS) summary statistics from bone mineral density (BMD) and fracture-related genetic variants. We employed an advanced statistical functional mapping method to investigate shared genetic architecture between muscle and bone, focusing on genes highly expressed in muscle tissue. Our analysis identified three genes, EPDR1, PKDCC, and SPTBN1, which are highly expressed in muscle tissue and previously unlinked to bone metabolism. About 90% and 85% of filtered Single-Nucleotide Polymorphisms were in the intronic and intergenic regions for the threshold at P≤5×10-8 and P≤5×10-100, respectively. EPDR1 was highly expressed in multiple tissues, including muscles, adrenal glands, blood vessels, and the thyroid. SPTBN1 was highly expressed in all 30 tissue types except blood, while PKDCC was highly expressed in all 30 tissue types except the brain, pancreas, and skin. Our study provides a framework for using GWAS findings to highlight functional evidence of crosstalk between multiple tissues based on shared genetic architecture between muscle and bone. Further research should focus on functional validation, multi-omics data integration, gene-environment interactions, and clinical relevance in musculoskeletal disorders.

A novel method for post-earthquake functional evaluation of city building portfolios

Enhancing the seismic resilience of city building portfolios is crucial to mitigating the impact of seismic disasters. A novel method is proposed to evaluate the post-earthquake functionality of city building portfolios, which can serve as the foundation for assessing the seismic resilience of cities. This method incorporates multiple dimensions of functional evaluation, ranging from structural and nonstructural components to city building portfolios, elucidating the mechanism of functional assemblies from lower to higher dimensions. The calculation of the physical functionality of individual buildings relies on the functionalities of their structural and nonstructural components, which are determined using the functional mapping method. The impacts of infrastructure failures on the functionality of individual buildings are explored using the hierarchical belief rule base inference method based on the evidential reasoning algorithm (BRBI-ER). A technique that combines Point of Interest analysis and visual interpretation is utilized to classify building portfolios into three types: single-function building portfolios, multi-function building portfolios, and integrated-function building portfolios. A cumulative functional correlation model and an integrated functional correlation model using BRBI-ER are established to evaluate the functionality of these types of building portfolios. The results can contribute to predicting the risk of functional losses before earthquakes, guiding the recovery process after earthquakes, and taking proactive measures to improve the seismic resilience of cities.

Data-efficient resting-state functional magnetic resonance imaging brain mapping with deep learning.

Resting-state functional MRI (RS-fMRI) enables the mapping of function within the brain and is emerging as an efficient tool for the presurgical evaluation of eloquent cortex. Models capable of reliable and precise mapping of resting-state networks (RSNs) with a reduced scanning time would lead to improved patient comfort while reducing the cost per scan. The aims of the present study were to develop a deep 3D convolutional neural network (3DCNN) capable of voxel-wise mapping of language (LAN) and motor (MOT) RSNs with minimal quantities of RS-fMRI data. Imaging data were gathered from multiple ongoing studies at Washington University School of Medicine and other thoroughly characterized, publicly available data sets. All study participants (n = 2252 healthy adults) were cognitively screened and completed structural neuroimaging and RS-fMRI. Random permutations of RS-fMRI regions of interest were used to train a 3DCNN. After training, model inferences were compared using varying amounts of RS-fMRI data from the control data set as well as 5 patients with glioblastoma multiforme. The trained model achieved 96% out-of-sample validation accuracy on data encompassing a large age range collected on multiple scanner types and varying sequence parameters. Testing on out-of-sample control data showed 97.9% similarity between results generated using either 50 or 200 RS-fMRI time points, corresponding to approximately 2.5 and 10 minutes, respectively (96.9% LAN, 96.3% MOT true-positive rate). In evaluating data from patients with brain tumors, the 3DCNN was able to accurately map LAN and MOT networks despite structural and functional alterations. Functional maps produced by the 3DCNN can inform surgical planning in patients with brain tumors in a time-efficient manner. The authors present a highly efficient method for presurgical functional mapping and thus improved functional preservation in patients with brain tumors.

Shortened Motor Evoked Potential Latency in the Epileptic Hemisphere of Children With Focal Epilepsy.

Motor evoked potential (MEP) amplitude and latency are acquired routinely during neuronavigated transcranial magnetic stimulation, a method of functional mapping of the motor cortex before epilepsy surgery. Although MEP amplitude is routinely used to generate a motor map, MEP latency in patients with focal epilepsy has not been studied systematically. Given that epilepsy may alter myelination, we tested whether intrinsic hand muscle MEPs obtained from the hemisphere containing a seizure focus differ in latency from MEPs collected from the opposite hemisphere. Latencies of abductor pollicis brevis MEPs were obtained during routine motor mapping by neuronavigated transcranial magnetic stimulation in children with intractable, unihemispheric focal epilepsy. The primary motor cortex was stimulated bilaterally in all cases. Only data from patients without a lesion involving the corticospinal tract were included. We tested whether abductor pollicis brevis MEP latency varied as a function of seizure focus lateralization. In the 17 patients who met the inclusion criteria, the mean latency of MEPs with amplitudes in the top and bottom quartiles was shorter in the epileptic hemisphere. Interhemispheric latency difference was greater in patients with lesional epilepsy than in those with nonlesional epilepsy (0.7 ± 0.4 vs. 0.1 ± 0.6 milliseconds, P = 0.02). Motor evoked potential latency was shortened in the epileptic hemisphere of children with focal epilepsy.

Differential impact of glycemic control and comorbid conditions on the neurophysiology underlying task switching in older adults with type 2 diabetes.

Type 2 diabetes is known to negatively affect higher order cognition and the brain, but the underlying mechanisms are not fully understood. In particular, glycemic control and common comorbidities are both thought to contribute to alterations in cortical neurophysiology in type 2 diabetes, but their specific impact remains unknown. The current study probed the dynamics underlying cognitive control in older participants with type 2 diabetes, with and without additional comorbid conditions (i.e., cardiovascular disease, nephropathy, peripheral neuropathy, retinopathy), using a task switching paradigm and a dynamic functional brain mapping method based on magnetoencephalography (MEG). We hypothesized that neural dynamics would be differentially impacted by the level of glycemic control (i.e., diabetes itself) and the burden of additional comorbid conditions. Supporting this hypothesis, our findings indicated separable, but widespread alterations across frontal, parietal, temporal and cerebellum regions in neural task-switch costs in type 2 diabetes that were differentially attributable to glycemic control and the presence of comorbid conditions. These effects were spatially non-overlapping and the effects were not statistically related to one another. Further, several of the effects that were related to the presence of comorbidities were associated with behavioral performance, indicating progressive deficits in brain function with extended disease. These findings provide insight on the underlying neuropathology and may inform future treatment plans to curtail the neural impact of type 2 diabetes.

The improvement of museum information flow based on paste functional mapping method

Abstract As a subsidiary institution of collecting and preserving cultural relics, human cultural heritages and developing information resources, museums are important places to display, disseminate and study excellent national cultures. With the development of the economy and the improvement of people's living standards, people's demand for spiritual culture is getting higher and higher, and museums are getting more and more attention from people. Thanks to the rapid development of computer technology, more and more museums are focusing on informatisation. This article will use the information system's functional mapping method based on the museum's improvement and test analysis, which can make the museum's business unit with the use of the unified system platform, under a unified, homogeneous standard data for the orderly organisation of information resources sharing and efficient, rapid building of information resources of lateral connection, make the administrative, business interaction and interrelated information collection with Word Perfect data integration, and create a museum management platform more conducive to innovative thinking. The innovation system mechanism, to improve the way of ZhanChen for the museum, to speed up the informatisation construction museum, make a museum of play to better spread knowledge, transfer civilisation, materialisation of education function and the important window displaying the world the outstanding civilisation achievement effect, and promote the development of cultural undertakings, where science has a very important realistic and far-reaching historical significance.

Clinical Validation of the Champagne Algorithm for Evoked Response Source Localization in Magnetoencephalography

Magnetoencephalography (MEG) is a robust method for non-invasive functional brain mapping of sensory cortices due to its exceptional spatial and temporal resolution. The clinical standard for MEG source localization of functional landmarks from sensory evoked responses is the equivalent current dipole (ECD) localization algorithm, known to be sensitive to initialization, noise, and manual choice of the number of dipoles. Recently many automated and robust algorithms have been developed, including the Champagne algorithm, an empirical Bayesian algorithm, with powerful abilities for MEG source reconstruction and time course estimation (Wipf et al. 2010; Owen et al. 2012). Here, we evaluate automated Champagne performance in a clinical population of tumor patients where there was minimal failure in localizing sensory evoked responses using the clinical standard, ECD localization algorithm. MEG data of auditory evoked potentials and somatosensory evoked potentials from 21 brain tumor patients were analyzed using Champagne, and these results were compared with equivalent current dipole (ECD) fit. Across both somatosensory and auditory evoked field localization, we found there was a strong agreement between Champagne and ECD localizations in all cases. Given resolution of 8mm voxel size, peak source localizations from Champagne were below 10mm of ECD peak source localization. The Champagne algorithm provides a robust and automated alternative to manual ECD fits for clinical localization of sensory evoked potentials and can contribute to improved clinical MEG data processing workflows.

The evaluation of central pain mechanisms in patients with microvascular angina

Abstract Funding Acknowledgements Type of funding sources: None. In patients with microvascular angina (MVA) besides of chest pain, a high neuronal activity of certain parts of the head (right anterior insula cortex) was revealed, which is not observed in the control in patients with coronary heart disease with coronary atherosclerosis. There is an opinion that the abnormal sensation of pain is caused not by myocardial ischemia, but by a violation of neuronal regulation. Functional MRI (fMRI) is currently a widely used method of functional mapping of the brain. The principle of the method is to register a BOLD signal (blood oxygen level-depended) from voxels (volumetric points) when examining the brain in response to the fulfillment of a task (paradigm). In response to the activation of a particular region of the brain, hemodynamic parameters change in it, which leads to a decrease in the level of deoxyhemoglobin and an increase in the level of oxyhemoglobin. With neuroimaging, this phenomenon is characterized by an increase in signal intensity in a series of T2 * images, the quantitative assessment of which allows indirectly determining the degree of neuronal activation. The study included 11 patients with MVA (3 men, 8 women). The average age of the patients was 61.45 ± 7.80 years. MVA was proved classic criteria and microvascular disorders (perfusion abnormalities) by cardiac PET. Neuroimaging examination included positron emission tomography scanning using 18-fluoro deoxyglucose (18F-FDG PET) and functional magnetic resonance imaging (fMRI) scanning using the GO / NOGO two-stimulus experimental paradigm. Throughout the study, fMRI and PET data were obtained for 11 patients with MVA and 20 healthy volunteers (control group). Results In patients with MVA, a decrease in neuronal activity was detected during the execution of actions ("GO" tests) compared with the norm in some brain structures: bilateral anterior and middle cingulate gyrus, additional motor region, postcentral gyrus, left in the islet cortex, on the right in the supramarginal gyrus. When ignoring the second stimulus ("P-P ignore."). A decrease compared with the norm was found bilaterally in the anterior and posterior cingulate cortex, the wedge, on the right in the cortex of the rolandic operculum and supramarginal gyrus. The detected clusters of decreased neuronal activity when performing actions and ignoring the second stimulus intersect bilaterally in the middle and anterior cingulate cortex, in the left paracentral lobe, and the right supramarginal gyrus. When suppressing actions ("NOGO samples"), no significant differences were found. According to PET, no significant changes in the level of glucose metabolism in patients with MVA compared with the control group were found. Conclusion In patients with MVA, a decrease in neuronal activity was found when performing actions compared to the norm in some brain structures.

Focal Cortical Surface Cooling is a Novel and Safe Method for Intraoperative Functional Brain Mapping

Electric cortical stimulation (ECS) has been the gold standard for intraoperative functional mapping in neurosurgery, yet it carries the risk of induced seizures. We assess the safety of focal cortical cooling (CC) as a potential alternative to ECS. We reviewed 40 patients (13 with tumor and 27 with mesial temporal lobe epilepsy) who underwent intraoperative CC at the University of Iowa Hospital and Clinics (CC group), of whom 38 underwent ECS preceding CC. Intraoperative and postoperative seizure incidence, postoperative neurologic deficits, and new postoperative radiographic findings were collected to assess CC safety. Fifty-five patients who underwent ECS mapping without CC (ECS-alone group) were reviewed as a control cohort. Another 25 patients who underwent anterior temporal lobectomy (ATL) without CC or ECS (no ECS/no CC-ATL group) were also reviewed to evaluate long-term effects of CC. Seventy-nine brain sites in the CC group were cooled, comprising inferior frontal gyrus (44%), precentral gyrus (39%), postcentral gyrus (6%), subcentral gyrus (4%), and superior temporal gyrus (6%). The incidence of intraoperative seizure(s) was 0% (CC group) and 3.6% (ECS-alone group). The incidence of seizure(s) within the first postoperative week did not significantly differ among CC (7.9%), ECS-alone (9.0%), and no ECS/no CC-ATL groups (12%). There was no significant difference in the incidence of postoperative radiographic change between CC (7.5%) and ECS-alone groups (5.5%). Long-term seizure outcome (Engel I+II) for mesial temporal epilepsy did not differ among CC (80%), ECS-alone (83.3%), and no ECS/no CC-ATL groups (83.3%). CC when used as an intraoperative mapping technique is safe and may complement ECS.

Mapping language function with task-based vs. resting-state functional MRI.

BackgroundUse of functional MRI (fMRI) in pre-surgical planning is a non-invasive method for pre-operative functional mapping for patients with brain tumors, especially tumors located near eloquent cortex. Currently, this practice predominantly involves task-based fMRI (T-fMRI). Resting state fMRI (RS-fMRI) offers an alternative with several methodological advantages. Here, we compare group-level analyses of RS-fMRI vs. T-fMRI as methods for language localization.PurposeTo contrast RS-fMRI vs. T-fMRI as techniques for localization of language function.MethodsWe analyzed data obtained in 35 patients who had both T-fMRI and RS-fMRI scans during the course of pre-surgical evaluation. The RS-fMRI data were analyzed using a previously trained resting-state network classifier. The T-fMRI data were analyzed using conventional techniques. Group-level results obtained by both methods were evaluated in terms of two outcome measures: (1) inter-subject variability of response magnitude and (2) sensitivity/specificity analysis of response topography, taking as ground truth previously reported maps of the language system based on intraoperative cortical mapping as well as meta-analytic maps of language task fMRI responses.ResultsBoth fMRI methods localized major components of the language system (areas of Broca and Wernicke) although not with equal inter-subject consistency. Word-stem completion T-fMRI strongly activated Broca's area but also several task-general areas not specific to language. RS-fMRI provided a more specific representation of the language system.ConclusionWe demonstrate several advantages of classifier-based mapping of language representation in the brain. Language T-fMRI activated task-general (i.e., not language-specific) functional systems in addition to areas of Broca and Wernicke. In contrast, classifier-based analysis of RS-fMRI data generated maps confined to language-specific regions of the brain.

Dispersive Instabilities in Passively Mode-Locked Integrated External-Cavity Surface-Emitting Lasers

We analyze the dynamics of passively mode-locked integrated external-cavity surface-emitting Lasers (MIXSELs) using a first-principle dynamical model based upon delay algebraic equations. We show that the third order dispersion stemming from the lasing micro-cavity induces a train of decaying satellites on the leading edge of the pulse. Due to the nonlinear interaction with carriers, these satellites may get amplified thereby destabilizing the mode-locked states. In the long cavity regime, the localized structures that exist below the lasing threshold are found to be deeply affected by this instability. As it originates from a global bifurcation of the saddle-node infinite period type, we explain why the pulses exhibit behaviors characteristic of excitable systems. Using the multiple time-scale and the functional mapping methods, we derive rigorously a master equation for MIXSELs in which third order dispersion is an essential ingredient. We compare the bifurcation diagram of both models and assess their good agreement.

Presurgical resting-state functional MRI language mapping with seed selection guided by regional homogeneity.

Resting-state functional MRI (rs-FMRI) has shown potential for presurgical mapping of eloquent cortex when a patient's performance on task-based FMRI is compromised. The seed-based analysis is a practical approach for detecting rs-FMRI functional networks; however, seed localization remains challenging for presurgical language mapping. Therefore, we proposed a data-driven approach to guide seed localization for presurgical rs-FMRI language mapping. Twenty-six patients with brain tumors located in left perisylvian regions had undergone task-based FMRI and rs-FMRI before tumor resection. For the seed-based rs-FMRI language mapping, a seeding approach that integrates regional homogeneity and meta-analysis maps (RH+MA) was proposed to guide the seed localization. Canonical and task-based seeding approaches were used for comparison. The performance of the 3 seeding approaches was evaluated by calculating the Dice coefficients between each rs-FMRI language mapping result and the result from task-based FMRI. With the RH+MA approach, selecting among the top 6 seed candidates resulted in the highest Dice coefficient for 81% of patients (21 of 26) and the top 9 seed candidates for 92% of patients (24 of 26). The RH+MA approach yielded rs-FMRI language mapping results that were in greater agreement with the results of task-based FMRI, with significantly higher Dice coefficients (P < .05) than that of canonical and task-based approaches within putative language regions. The proposed RH+MA approach outperformed the canonical and task-based seed localization for rs-FMRI language mapping. The results suggest that RH+MA is a robust and feasible method for seed-based functional connectivity mapping in clinical practice.

Accelerated Clustered Sparse Acquisition to Improve Functional MRI for Mapping Language Functions.

Functional magnetic resonance imaging (fMRI) is a useful method for noninvasive presurgical functional mapping. However, the scanner environment is inherently unsuitable for the examination of auditory and language functions, due to the loud acoustic noise produced by the scanner. Interleaved acquisition methods alleviate this problem by providing a silent period for stimulus presentation and/or response control (sparse sampling) but at the expense of a diminished amount of data collected. There are possible improvements to these sparse acquisition methods that increase the amount of data by acquiring several images per event (clustered sampling). We tested accelerated clustered fMRI acquisition in comparison with conventional sparse sampling in a pilot study. The clustered and sparse acquisition techniques (7.4 minutes scanning time per protocol) were directly compared in 15 healthy subjects (8 men; mean age: 24 ± 3 years) using both a motor (tongue movement) and a language (overt picture-naming) task. Functional imaging data were analyzed using Statistical Parametric Mapping software (SPM12 Wellcome Department of Imaging Neuroscience, London, UK). For both tasks, activation levels were compared and Euclidean distances (EDs) between cluster centers (i.e., local activation maxima and centers of gravity) were calculated. Overlaps and laterality indices were computed for the picture-naming task. In addition, the feasibility of the clustered acquisition protocol in a clinical setting was assessed in one pilot patient. For both tasks, activation levels were higher using the clustered acquisition protocol, reflected by bigger cluster sizes (p < 0.05). Mean ED between cluster centers ranged between 9.9 ± 5.4 mm (left superior temporal gyrus; centers of gravity) and 16.6 ± 13.2 mm (left inferior frontal gyrus; local activation maxima) for the picture-naming task. Overlaps between sparse and clustered acquisition reached 88% (Simpson overlap coefficient). A similar activation pattern for both acquisition methods was also confirmed in the clinical case. Despite some drawbacks inherent to the acquisition technique, the clustered sparse sampling protocol showed increased sensitivity for activation in language-related cortical regions with short scanning times. Such scanning techniques may be particularly advantageous for investigating patients with contraindications for long scans (e.g., reduced attention span).

Presurgical Functional Cortical Mapping Using Electromagnetic Source Imaging.

Preoperative localization of functionally eloquent cortex (functional cortical mapping) is common clinical practice in order to avoid or reduce postoperative morbidity. This review aims at providing a general overview of magnetoencephalography (MEG) and high-density electroencephalography (hdEEG) based methods and their clinical role as compared to common alternatives for functional cortical mapping of (1) verbal language function, (2) sensorimotor cortex, (3) memory, (4) visual, and (5) auditory cortex. We highlight strengths, weaknesses and limitations of these functional cortical mapping modalities based on findings in the recent literature. We also compare their performance relative to other non-invasive functional cortical mapping methods, such as functional Magnetic Resonance Imaging (fMRI), Transcranial Magnetic Stimulation (TMS), and to invasive methods like the intracarotid Amobarbital Test (WADA-Test) or intracranial investigations.

Chapter 31 - The auditory and association cortex and language evaluation methods

This chapter presents a summary of current notions regarding cortical specialization for language and a description of the methods employed for the assessment of that specialization. We distinguish between the "canonical" model of language specialization as it evolved from the early observations of Broca and Wernicke, implicating the inferior frontal gyrus and the posterior temporal cortex of the speech dominant hemisphere (usually the left) and its modern variants that are based on both detailed studies of lesion-symptom correlations and on the results of functional brain mapping methods. The latter fall into two categories. The first includes the invasive ones, namely the Wada procedure for assessing hemispheric dominance for speech and cortical stimulation mapping (whether intraoperative or extraoperative) for identifying cortical nodes or "hubs" of the neuronal network for language. The second category includes the noninvasive methods of functional magnetic resonance imaging, magnetoencephalography, and transcranial magnetic stimulation used for both assessment of hemispheric dominance for language and for localization of the cortical nodes of the language network. The advantages and the shortcomings of all methods are juxtaposed to facilitate selection of particular methods of assessment of the locus of the language network in particular cases.

BS25. Language inhibition and motor response thresholds during extra-operative cortical stimulation mapping

Introduction Electrical cortical stimulation (ECS) is the clinical standard for brain mapping to define the functionally eloquent cortex in patients undergoing pre-surgical evaluation with intracranial electrodes. This study evaluated thresholds for language inhibition and motor response during ECS and their determinants. Methods A retrospective review of clinical information and extra-operative electrocorticography (ECoG) recordings was performed. The thresholds for functional responses were determined and compared with after-discharge (AD) thresholds. Multivariate models were used to evaluate predictors of functional thresholds. Results A total of 122 children were included. The mean language threshold was 7.4 ( ± 3.0) mA. 40/47 (85%) of patients with language response during ECS also had ADs. Language thresholds were found to be equal to or higher than AD thresholds in 34/40 (85%) patients. The mean motor threshold was 5.4 ( ± 2.8) mA. 71/85(83.5%) of patients with motor response during ECS also had ADs. Motor thresholds were found to be equal to or higher than AD thresholds in 47/71 (66%) patients. Minimum AD threshold was a significant determinant of minimum language threshold (regression co-efficient 0.446, 95% CI −0.001 to 0.892, p = 0.050) and minimum motor threshold (regression co-efficient 0.664, 95%CI 0.058 to 1.270, p = 0.034). Conclusion AD threshold was a significant determinant of language and motor thresholds. Most children with functional response during ECS also had ADs, with the functional thresholds being equal to or higher than AD thresholds. These findings underscore a potential pitfall in functional cortex localization with ECS findings and emphasize the need for a functional mapping method with improved neurophysiologic validity, especially in children.

SINGLE CENTER CLINICAL EXPERIENCE USING ISOCHRONAL LATE ACTIVATION MAPPING FOR ABLATION OF VENTRICULAR TACHYCARDIA

Given hemodynamically instability of most ventricular tachycardias (VT), mapping and ablating scar based arrhythmias during sinus rhythm is of clinical utility. Isochronal late activation mapping (ILAM) is a functional mapping method which may better guide ablation of abnormal electrograms. All

Valsalva-induced elevation of intracranial pressure selectively decouples deoxygenated hemoglobin concentration from neuronal activation and functional brain imaging capability

During neuronal activation, neurovascular coupling leads to a local decrease of deoxygenated hemoglobin concentration (deoxy-Hb) and thus forms the basis of many functional brain mapping methods. In animals, an elevated intracranial pressure (ICP) can attenuate or even reverse this deoxy-Hb signaling. To study the effect of an elevated ICP on functional brain imaging in humans, we used different breathing tasks to modify ICP and analyzed the resulting effect on neurovascular coupling in the motor cortex. Functional near-infrared spectroscopy (fNIRS) was performed on 45 subjects during alternating conditions of finger tapping and resting state combined with four different breathing maneuvers (normal breathing (NB), breath holding without Valsalva maneuver (BH), Valsalva maneuver with 15 mm Hg forced expiratory pressure against resistance (V15) and Valsalva maneuver with 35 mm Hg forced expiratory pressure against resistance (V35)) in randomized order. With escalation of breathing tasks the median amplitude of the functional deoxy-Hb decrease during finger tapping became smaller. In contrast, functional oxygenated hemoglobin concentration (oxy-Hb) and total hemoglobin concentration (total-Hb) responses did not show a significant alteration. The functional oxy-Hb map evoked by finger tapping withstood Valsalva challenges while the functional deoxy-Hb map identified the correct motor cortex in normal breathing conditions only and did not reveal a functional contrast during Valsalva maneuvers. In summary, we conclude that during ICP elevation, deoxy-Hb is not a reliable basis for functional brain imaging. This suggests that the validity of BOLD fMRI during increased ICP might be impaired.

Planar implantable sensor for in vivo measurement of cellular oxygen metabolism in brain tissue

BackgroundBrain imaging methods are continually improving. Imaging of the cerebral cortex is widely used in both animal experiments and charting human brain function in health and disease. Among the animal models, the rodent cerebral cortex has been widely used because of patterned neural representation of the whiskers on the snout and relative ease of activating cortical tissue with whisker stimulation. New methodWe tested a new planar solid-state oxygen sensor comprising a polymeric film with a phosphorescent oxygen-sensitive coating on the working side, to monitor dynamics of oxygen metabolism in the cerebral cortex following sensory stimulation. ResultsSensory stimulation led to changes in oxygenation and deoxygenation processes of activated areas in the barrel cortex. We demonstrate the possibility of dynamic mapping of relative changes in oxygenation in live mouse brain tissue with such a sensor. Comparison with existing methodOxygenation-based functional magnetic resonance imaging (fMRI) is very effective method for functional brain mapping but have high costs and limited spatial resolution. Optical imaging of intrinsic signal (IOS) does not provide the required sensitivity, and voltage-sensitive dye optical imaging (VSDi) has limited applicability due to significant toxicity of the voltage-sensitive dye. Our planar solid-state oxygen sensor imaging approach circumvents these limitations, providing a simple optical contrast agent with low toxicity and rapid application. ConclusionsThe planar solid-state oxygen sensor described here can be used as a tool in visualization and real-time analysis of sensory-evoked neural activity in vivo. Further, this approach allows visualization of local neural activity with high temporal and spatial resolution.