Weighing brain activity with the balance: Angelo Mosso's original manuscripts come to light

Future of neurocritical care: Integrating neurophysics, multimodal monitoring, and machine learning

Multimodal monitoring (MMM) in the intensive care unit (ICU) has become increasingly sophisticated with the integration of neurophysical principles. However, the challenge remains to select and interpret the most appropriate combination of neuromonitoring modalities to optimize patient outcomes. This manuscript reviewed current neuromonitoring tools, focusing on intracranial pressure, cerebral electrical activity, metabolism, and invasive and noninvasive autoregulation monitoring. In addition, the integration of advanced machine learning and data science tools within the ICU were discussed. Invasive monitoring includes analysis of intracranial pressure waveforms, jugular venous oximetry, monitoring of brain tissue oxygenation, thermal diffusion flowmetry, electrocorticography, depth electroencephalography, and cerebral microdialysis. Noninvasive measures include transcranial Doppler, tympanic membrane displacement, near-infrared spectroscopy, optic nerve sheath diameter, positron emission tomography, and systemic hemodynamic monitoring including heart rate variability analysis. The neurophysical basis and clinical relevance of each method within the ICU setting were examined. Machine learning algorithms have shown promise by helping to analyze and interpret data in real time from continuous MMM tools, helping clinicians make more accurate and timely decisions. These algorithms can integrate diverse data streams to generate predictive models for patient outcomes and optimize treatment strategies. MMM, grounded in neurophysics, offers a more nuanced understanding of cerebral physiology and disease in the ICU. Although each modality has its strengths and limitations, its integrated use, especially in combination with machine learning algorithms, can offer invaluable information for individualized patient care.

Functional magnetic particle imaging (fMPI) of cerebrovascular changes in the rat brain during hypercapnia

Objective.Non-invasive functional brain imaging modalities are limited in number, each with its own complex trade-offs between sensitivity, spatial and temporal resolution, and the directness with which the measured signals reflect neuronal activation. Magnetic particle imaging (MPI) directly maps the cerebral blood volume (CBV), and its high sensitivity derives from the nonlinear magnetization of the superparamagnetic iron oxide nanoparticle (SPION) tracer confined to the blood pool. Our work evaluates functional MPI (fMPI) as a new hemodynamic functional imaging modality by mapping the CBV response in a rodent model where CBV is modulated by hypercapnic breathing manipulation.Approach.The rodent fMPI time-series data were acquired with a mechanically rotating field-free line MPI scanner capable of 5 s temporal resolution and 3 mm spatial resolution. The rat's CBV was modulated for 30 min with alternating 5 min hyper-/hypocapnic states, and processed using conventional fMRI tools. We compare our results to fMRI responses undergoing similar hypercapnia protocols found in the literature, and reinforce this comparison in a study of one rat with 9.4T BOLD fMRI using the identical protocol.Main results.The initial image in the time-series showed mean resting brain voxel SNR values, averaged across rats, of 99.9 following the first 10 mg kg-1SPION injection and 134 following the second. The time-series fit a conventional General Linear Model with a 15%-40% CBV change and a peak pixel CNR between 12 and 29, 2-6× higher than found in fMRI.Significance.This work introduces a functional modality with high sensitivity, although currently limited spatial and temporal resolution. With future clinical-scale development, a large increase in sensitivity could supplement other modalities and help transition functional brain imaging from a neuroscience tool focusing on population averages to a clinically relevant modality capable of detecting differences in individual patients.

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.

Synthesis, characterization, and bioevaluation of 99mTc nitrido-oxiracetam as a brain imaging model

In this work, the radiotracer [99mTc]nitrido-oxiracetam complex was labeled in the presence of 99mTc-nitrido as a core. In order to get the highest radiochemical purity, many effective factors have been studied such as temperature of the reaction, time of the reaction, the pH of the reaction mixture, substrate amount, and stability to give high percent more than 99%. Finally, biodistribution studies have been indicated the convenience of [99mTc]nitrido-oxiracetam as a new radiotracer that could be used in brain imaging. Giving a maximum uptake of 10.6% at 30 min post injection.

The development and evolution of "cerebral thermometry": The physiology underlying a nineteenth-century approach to cerebral localization and neurological diagnosis

Surface thermometers were developed in the latter half of the nineteenth century. From the 1850s through the 1880s, collaborations between physicians, research scientists, and instrument makers produced clear improvements in the technology to measure cranial surface temperatures, with development of self-registering mercury surface thermometers resistant to pressure and little influenced by ambient temperature, apparatus for recording cranial surface temperatures from multiple stations simultaneously, and development of thermoelectric apparatus. Physiologic studies of cranial surface thermometry were conducted over a quarter century from 1861 to 1886. Beginning in the 1860s Albers in Bonn, Germany, and Lombard at Harvard and later in England systematically investigated surface temperatures on the head using surface thermometers and thermoelectric apparatus; they demonstrated that head temperatures were variable over time and across individuals and were not clearly influenced by thinking or muscular contraction but were influenced by ambient air temperature. In 1880 Amidon in the United States claimed that cranial surface thermometry during exertion produced localized increases in surface temperature on the contralateral scalp in a specific pattern ("external motive areas") indicating underlying brain areas responsible for each movement. Amidon's results were not reproduced by experienced physiologists in England or France. Contemporaries recognized that significant technical and practical problems limited the accuracy and reliability of cranial surface thermometry. Physiological studies of cranial surface thermometry ended in the mid 1880s, although some clinicians who were early advocates promoted its use in clinical contexts into the early twentieth century.

An Overview of Functional Magnetic Resonance Imaging Techniques for Organizational Research

Functional magnetic resonance imaging is a galvanizing tool for behavioral scientists. It provides a means by which to see what the brain does while a person thinks, acts, or perceives, without invasive procedures. In this, fMRI affords us a relatively easy manner by which to peek under the hood of behavior and into the brain. Characterizing behavior with a neural correlate allows us to support or discard theoretical assumptions about the brain and behavior, to identify markers for individual and group differences. The increasing popularity of fMRI is facilitated by the apparent ease of data acquisition and analysis. This comes at a price: low signal-to-noise ratios, limitations in experimental design, and the difficulty in correctly applying and interpreting statistical tests are just a few of the pitfalls that have brought into question the reliability and validity of published fMRI data. Here, we aim to provide a general overview of the method, with an emphasis on fMRI and its analysis. Our goal is to provide the novice user with a comprehensive framework to get started on designing an imaging experiment in humans.

Radiocomplexation and bioevaluation of 99mTc nitrido-piracetam as a model for brain imaging

The aim of the work is to radiolabel a piracetam using [99mTc≡N]2+core in order to give a 99mTcN-labeled piracetam complex, that is expected to concentrate in brain organ by AMPA receptors. The complex was prepared with high radiochemical purity (>98.0) and maintained stability throughout the working period (8 h) using different quality controls. Biodistribution investigation showed that, the maximum uptake of the complex in the brain was 13.5±0.12% at 5 min post injection (p.i.) of the injected dose/g which retained till 2 h post-injection.

A neuronal MCT2 knockdown in the rat somatosensory cortex reduces both the NMR lactate signal and the BOLD response during whisker stimulation

Although several in vitro and ex vivo evidence support the existence of lactate exchange between astrocytes and neurons, a direct demonstration in vivo is still lacking. In the present study, a lentiviral vector carrying a short hairpin RNA (shRNA) was used to downregulate the expression of the monocarboxylate transporter type 2 (MCT2) in neurons of the rat somatosensory cortex (called S1BF) by ~ 25%. After one hour of whisker stimulation, HRMAS 1H-NMR spectroscopy analysis of S1BF perchloric acid extracts showed that while an increase in lactate content is observed in both uninjected and shRNA-control injected extracts, such an effect was abrogated in shMCT2 injected rats. A 13C-incorporation analysis following [1-13C]glucose infusion during the stimulation confirmed that the elevated lactate observed during activation originates from newly synthesized [3-13C]lactate, with blood-derived [1-13C]glucose being the precursor. Moreover, the analysis of the 13C-labeling of glutamate in position C3 and C4 indicates that upon activation, there is an increase in TCA cycle velocity for control rats while a decrease is observed for MCT2 knockdown animals. Using in vivo localized 1H-NMR spectroscopy, an increase in lactate levels is observed in the S1BF area upon whisker stimulation for shRNA-control injected rats but not for MCT2 knockdown animals. Finally, while a robust BOLD fMRI response was evidenced in control rats, it was absent in MCT2 knockdown rats. These data not only demonstrate that glucose-derived lactate is locally produced following neuronal activation but also suggest that its use by neurons via MCT2 is probably essential to maintain synaptic activity within the barrel cortex.

Brain Vascular Imaging Techniques

Recent major improvements in a number of imaging techniques now allow for the study of the brain in ways that could not be considered previously. Researchers today have well-developed tools to specifically examine the dynamic nature of the blood vessels in the brain during development and adulthood; as well as to observe the vascular responses in disease situations in vivo. This review offers a concise summary and brief historical reference of different imaging techniques and how these tools can be applied to study the brain vasculature and the blood-brain barrier integrity in both healthy and disease states. Moreover, it offers an overview on available transgenic animal models to study vascular biology and a description of useful online brain atlases.

Neuroimaging of Central Sensitivity Syndromes: Key Insights from the Scientific Literature

Central sensitivity syndromes are characterized by distressing symptoms, such as pain and fatigue, in the absence of clinically obvious pathology. The scientific underpinnings of these disorders are not currently known. Modern neuroimaging techniques promise new insights into mechanisms mediating these postulated syndromes. We review the results of neuroimaging applied to five central sensitivity syndromes: fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, temporomandibular joint disorder, and vulvodynia syndrome. Neuroimaging studies of basal metabolism, anatomic constitution, molecular constituents, evoked neural activity, and treatment effect are compared across all of these syndromes. Evoked sensory paradigms reveal sensory augmentation to both painful and nonpainful stimulation. This is a transformative observation for these syndromes, which were historically considered to be completely of hysterical or feigned in origin. However, whether sensory augmentation represents the cause of these syndromes, a predisposing factor, an endophenotype, or an epiphenomenon cannot be discerned from the current literature. Further, the result from cross-sectional neuroimaging studies of basal activity, anatomy, and molecular constituency are extremely heterogeneous within and between the syndromes. A defining neuroimaging "signature" cannot be discerned for any of the particular syndromes or for an over-arching central sensitization mechanism common to all of the syndromes. Several issues confound initial attempts to meaningfully measure treatment effects in these syndromes. At this time, the existence of "central sensitivity syndromes" is based more soundly on clinical and epidemiological evidence. A coherent picture of a "central sensitization" mechanism that bridges across all of these syndromes does not emerge from the existing scientific evidence.

Repairing the Brain by SCF+G-CSF Treatment at 6 Months Postexperimental Stroke: Mechanistic Determination of the Causal Link Between Neurovascular Regeneration and Motor Functional Recovery

Stroke, a leading cause of adult disability in the world, is a severe medical condition with limited treatment. Physical therapy, the only treatment available for stroke rehabilitation, appears to be effective within 6 months post-stroke. Here, we have mechanistically determined the efficacy of combined two hematopoietic growth factors, stem cell factor (SCF) and granulocyte-colony stimulating factor (G-CSF; SCF + G-CSF), in brain repair 6 months after cortical infarct induction in the transgenic mice carrying yellow fluorescent protein in Layer V pyramidal neurons (Thy1-YFP-H). Using a combination of live brain imaging, whole brain imaging, molecular manipulation, synaptic and vascular assessments, and motor function examination, we found that SCF + G-CSF promoted mushroom spine formation, enlarged postsynaptic membrane size, and increased postsynaptic density-95 accumulation and blood vessel density in the peri-infarct cavity cortex; and that SCF + G-CSF treatment improved motor functional recovery. The SCF + G-CSF-enhanced motor functional recovery was dependent on the synaptic and vascular regeneration in the peri-infarct cavity cortex. These data suggest that a stroke-damaged brain is repairable by SCF + G-CSF even 6 months after the lesion occurs. This study provides novel insights into the development of new restorative strategies for stroke recovery.

The Brain from Within

Functional magnetic resonance imaging (fMRI) provides a powerful way to visualize brain functions and observe brain activity in response to tasks or thoughts. It allows displaying brain damages that can be quantified and linked to neurobehavioral deficits. fMRI can potentially draw a new cartography of brain functional areas, allow us to understand aspects of brain function evolution or even breach the wall into cognition and consciousness. However, fMRI is not deprived of pitfalls, such as limitation in spatial resolution, poor reproducibility, different time scales of fMRI measurements and neuron action potentials, low statistical values. Thus, caution is needed in the assessment of fMRI results and conclusions. Additional diagnostic techniques based on MRI such as arterial spin labeling (ASL) and the measurement of diffusion tensor imaging (DTI) provide new tools to assess normal brain development or disruption of anatomical networks in diseases. A cutting edge of recent research uses fMRI techniques to establish a "map" of neural connections in the brain, or "connectome". It will help to develop a map of neural connections and thus understand the operation of the network. New applications combining fMRI and real time visualization of one's own brain activity (rtfMRI) could empower individuals to modify brain response and thus could enable researchers or institutions to intervene in the modification of an individual behavior. The latter in particular, as well as the concern about the confidentiality and storage of sensitive information or fMRI and lie detectors forensic use, raises new ethical questions.

Dull Brains, Mountaineers, and Mosso: Hypoxic Words from on High

Dull and hypoxic brains have been a frequent subject in the medical and mountaineering literature. Deterioration of cognitive and other neurological function occurs at high altitude, with or without high altitude cerebral edema. This historical essay explores a 2014 first-ever English translation of cerebral blood flow studies by nineteenth century physiologist Angelo Mosso. Some of the medical history and physiology of brain function is discussed, but much of the style focuses on quotations from the writings of mountaineers and mountaineering physicians to provide color commentary about dull brains at high altitude.

Control of cerebrovascular patterning by neural activity during postnatal development

The brain represents only a small portion of the body mass and yet consumes almost a quarter of the available energy, and has a limited ability to store energy. The brain is therefore highly dependent on oxygen and nutrient supply from the blood circulation, which makes it vulnerable to vascular pathologies. Key vascular determinants will ensure proper brain maturation and function: the establishment of vascular networks, the formation of the blood-brain barrier, and the regulation of blood flow. Recent evidence suggests that the phenomenon of neurovascular coupling, during which increased neural activity normally leads to increased blood flow, is not functional until few weeks after birth, implying that the developing brain must rely on alternative mechanisms to adequately couple blood supply to increasing energy demands. This review will focus on these alternative mechanisms, which have been partly elucidated recently via the demonstration that neural activity influences the maturation of cerebrovascular networks. We also propose possible mechanisms underlying activity-induced vascular plasticity.

Efficient Blockwise Permutation Tests Preserving Exchangeability

In this paper, we present a new blockwise permutation test approach based on the moments of the test statistic. The method is of importance to neuroimaging studies. In order to preserve the exchangeability condition required in permutation tests, we divide the entire set of data into certain exchangeability blocks. In addition, computationally efficient moments-based permutation tests are performed by approximating the permutation distribution of the test statistic with the Pearson distribution series. This involves the calculation of the first four moments of the permutation distribution within each block and then over the entire set of data. The accuracy and efficiency of the proposed method are demonstrated through simulated experiment on the magnetic resonance imaging (MRI) brain data, specifically the multi-site voxel-based morphometry analysis from structural MRI (sMRI).