Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 32
Filtrar
1.
Neuroimage ; 237: 118091, 2021 08 15.
Artículo en Inglés | MEDLINE | ID: mdl-33991698

RESUMEN

High-resolution fMRI in the sub-millimeter regime allows researchers to resolve brain activity across cortical layers and columns non-invasively. While these high-resolution data make it possible to address novel questions of directional information flow within and across brain circuits, the corresponding data analyses are challenged by MRI artifacts, including image blurring, image distortions, low SNR, and restricted coverage. These challenges often result in insufficient spatial accuracy of conventional analysis pipelines. Here we introduce a new software suite that is specifically designed for layer-specific functional MRI: LayNii. This toolbox is a collection of command-line executable programs written in C/C++ and is distributed opensource and as pre-compiled binaries for Linux, Windows, and macOS. LayNii is designed for layer-fMRI data that suffer from SNR and coverage constraints and thus cannot be straightforwardly analyzed in alternative software packages. Some of the most popular programs of LayNii contain 'layerification' and columnarization in the native voxel space of functional data as well as many other layer-fMRI specific analysis tasks: layer-specific smoothing, model-based vein mitigation of GE-BOLD data, quality assessment of artifact dominated sub-millimeter fMRI, as well as analyses of VASO data.


Asunto(s)
Encéfalo/diagnóstico por imagen , Encéfalo/fisiología , Neuroimagen Funcional , Procesamiento de Imagen Asistido por Computador , Imagen por Resonancia Magnética , Programas Informáticos , Neuroimagen Funcional/métodos , Humanos , Procesamiento de Imagen Asistido por Computador/métodos , Imagen por Resonancia Magnética/métodos
2.
Proc Natl Acad Sci U S A ; 115(51): E12073-E12082, 2018 12 18.
Artículo en Inglés | MEDLINE | ID: mdl-30510000

RESUMEN

Cholinergic neuromodulation is involved in all aspects of sensory processing and is crucial for processes such as attention, learning and memory, etc. However, despite the known roles of acetylcholine (ACh), we still do not how to disentangle ACh contributions from sensory or task-evoked changes in functional magnetic resonance imaging (fMRI). Here, we investigated the effects of local injection of ACh on fMRI and neural signals in the primary visual cortex (V1) of anesthetized macaques by combining pharmaco-based MRI (phMRI) with electrophysiological recordings, using single electrodes and electrode arrays. We found that local injection of ACh elicited two distinct profiles of fMRI and neurophysiological activity, depending on the distance from the injector. Near the injection site, we observed an increase in the baseline blood oxygen-level-dependent (BOLD) and cerebral blood flow (CBF) responses, while their visual modulation decreased. In contrast, further from the injection site, we observed an increase in the visually induced BOLD and CBF modulation without changes in baseline. Neurophysiological recordings suggest that the spatial correspondence between fMRI responses and neural activity does not change in the gamma, high-gamma, and multiunit activity (MUA) bands. The results near the injection site suggest increased inhibitory drive and decreased metabolism, contrasting to the far region. These changes are thought to reflect the kinetics of ACh and its metabolism to choline.


Asunto(s)
Acetilcolina/farmacología , Imagen por Resonancia Magnética/métodos , Neurofisiología/métodos , Corteza Visual/efectos de los fármacos , Corteza Visual/diagnóstico por imagen , Acetilcolina/administración & dosificación , Acetilcolina/metabolismo , Animales , Encéfalo/irrigación sanguínea , Encéfalo/diagnóstico por imagen , Mapeo Encefálico/métodos , Circulación Cerebrovascular/efectos de los fármacos , Colina/metabolismo , Colinérgicos/farmacología , Fenómenos Electrofisiológicos , Metabolismo Energético , Femenino , Inyecciones , Cinética , Macaca mulatta , Masculino , Oxígeno/sangre , Estimulación Luminosa , Corteza Visual/irrigación sanguínea , Corteza Visual/metabolismo
3.
Neuroimage ; 208: 116463, 2020 03.
Artículo en Inglés | MEDLINE | ID: mdl-31862526

RESUMEN

The human brain coordinates a wide variety of motor activities. On a large scale, the cortical motor system is topographically organized such that neighboring body parts are represented by neighboring brain areas. This homunculus-like somatotopic organization along the central sulcus has been observed using neuroimaging for large body parts such as the face, hands and feet. However, on a finer scale, invasive electrical stimulation studies show deviations from this somatotopic organization that suggest an organizing principle based on motor actions rather than body part moved. It has not been clear how the action-map organization principle of the motor cortex in the mesoscopic (sub-millimeter) regime integrates into a body map organization principle on a macroscopic scale (cm). Here we developed and applied advanced mesoscopic (sub-millimeter) fMRI and analysis methodology to non-invasively investigate the functional organization topography across columnar and laminar structures in humans. Compared to previous methods, in this study, we could capture locally specific blood volume changes across entire brain regions along the cortical curvature. We find that individual fingers have multiple mirrored representations in the primary motor cortex depending on the movements they are involved in. We find that individual digits have cortical representations up to 3 â€‹mm apart from each other arranged in a column-like fashion. These representations are differentially engaged depending on whether the digits' muscles are used for different motor actions such as flexion movements, like grasping a ball or retraction movements like releasing a ball. This research provides a starting point for non-invasive investigation of mesoscale topography across layers and columns of the human cortex and bridges the gap between invasive electrophysiological investigations and large coverage non-invasive neuroimaging.


Asunto(s)
Mapeo Encefálico , Dedos/fisiología , Imagen por Resonancia Magnética , Actividad Motora/fisiología , Corteza Motora/anatomía & histología , Corteza Motora/fisiología , Adulto , Humanos , Corteza Motora/diagnóstico por imagen
4.
Clin Sci (Lond) ; 132(8): 851-868, 2018 04 30.
Artículo en Inglés | MEDLINE | ID: mdl-29712883

RESUMEN

Cerebral small vessel disease (SVD) is a major contributor to stroke, cognitive impairment and dementia with limited therapeutic interventions. There is a critical need to provide mechanistic insight and improve translation between pre-clinical research and the clinic. A 2-day workshop was held which brought together experts from several disciplines in cerebrovascular disease, dementia and cardiovascular biology, to highlight current advances in these fields, explore synergies and scope for development. These proceedings provide a summary of key talks at the workshop with a particular focus on animal models of cerebral vascular disease and dementia, mechanisms and approaches to improve translation. The outcomes of discussion groups on related themes to identify the gaps in knowledge and requirements to advance knowledge are summarized.


Asunto(s)
Enfermedades de los Pequeños Vasos Cerebrales/etiología , Investigación Biomédica Traslacional , Animales , Humanos
5.
Neuroimage ; 107: 23-33, 2015 Feb 15.
Artículo en Inglés | MEDLINE | ID: mdl-25479018

RESUMEN

Cortical layer-dependent high (sub-millimeter) resolution functional magnetic resonance imaging (fMRI) in human or animal brain can be used to address questions regarding the functioning of cortical circuits, such as the effect of different afferent and efferent connectivities on activity in specific cortical layers. The sensitivity of gradient echo (GE) blood oxygenation level-dependent (BOLD) responses to large draining veins reduces its local specificity and can render the interpretation of the underlying laminar neural activity impossible. The application of the more spatially specific cerebral blood volume (CBV)-based fMRI in humans has been hindered by the low sensitivity of the noninvasive modalities available. Here, a vascular space occupancy (VASO) variant, adapted for use at high field, is further optimized to capture layer-dependent activity changes in human motor cortex at sub-millimeter resolution. Acquired activation maps and cortical profiles show that the VASO signal peaks in gray matter at 0.8-1.6mm depth, and deeper compared to the superficial and vein-dominated GE-BOLD responses. Validation of the VASO signal change versus well-established iron-oxide contrast agent based fMRI methods in animals showed the same cortical profiles of CBV change, after normalization for lamina-dependent baseline CBV. In order to evaluate its potential of revealing small lamina-dependent signal differences due to modulations of the input-output characteristics, layer-dependent VASO responses were investigated in the ipsilateral hemisphere during unilateral finger tapping. Positive activation in ipsilateral primary motor cortex and negative activation in ipsilateral primary sensory cortex were observed. This feature is only visible in high-resolution fMRI where opposing sides of a sulcus can be investigated independently because of a lack of partial volume effects. Based on the results presented here, we conclude that VASO offers good reproducibility, high sensitivity and lower sensitivity than GE-BOLD to changes in larger vessels, making it a valuable tool for layer-dependent fMRI studies in humans.


Asunto(s)
Volumen Sanguíneo/fisiología , Encéfalo/anatomía & histología , Corteza Cerebral/anatomía & histología , Corteza Cerebral/fisiología , Circulación Cerebrovascular/fisiología , Adulto , Algoritmos , Animales , Vasos Sanguíneos/anatomía & histología , Corteza Cerebral/irrigación sanguínea , Vías Eferentes/anatomía & histología , Vías Eferentes/fisiología , Femenino , Compuestos Férricos , Dedos/inervación , Dedos/fisiología , Haplorrinos , Humanos , Procesamiento de Imagen Asistido por Computador , Imagen por Resonancia Magnética , Masculino , Corteza Motora/anatomía & histología , Corteza Motora/fisiología , Movimiento/fisiología , Oxígeno/sangre , Ratas , Relación Señal-Ruido , Adulto Joven
6.
Neuroimage ; 97: 349-62, 2014 Aug 15.
Artículo en Inglés | MEDLINE | ID: mdl-24742920

RESUMEN

Decreases in stimulus-dependent blood oxygenation level dependent (BOLD) signal and their underlying neurovascular origins have recently gained considerable interest. In this study a multi-echo, BOLD-corrected vascular space occupancy (VASO) functional magnetic resonance imaging (fMRI) technique was used to investigate neurovascular responses during stimuli that elicit positive and negative BOLD responses in human brain at 7 T. Stimulus-induced BOLD, cerebral blood volume (CBV), and cerebral blood flow (CBF) changes were measured and analyzed in 'arterial' and 'venous' blood compartments in macro- and microvasculature. We found that the overall interplay of mean CBV, CBF and BOLD responses is similar for tasks inducing positive and negative BOLD responses. Some aspects of the neurovascular coupling however, such as the temporal response, cortical depth dependence, and the weighting between 'arterial' and 'venous' contributions, are significantly different for the different task conditions. Namely, while for excitatory tasks the BOLD response peaks at the cortical surface, and the CBV change is similar in cortex and pial vasculature, inhibitory tasks are associated with a maximum negative BOLD response in deeper layers, with CBV showing strong constriction of surface arteries and a faster return to baseline. The different interplays of CBV, CBF and BOLD during excitatory and inhibitory responses suggests different underlying hemodynamic mechanisms.


Asunto(s)
Encéfalo/anatomía & histología , Imagen Eco-Planar/métodos , Oxígeno/sangre , Adulto , Animales , Vasos Sanguíneos/anatomía & histología , Vasos Sanguíneos/ultraestructura , Capilares/anatomía & histología , Capilares/ultraestructura , Circulación Cerebrovascular/fisiología , Movimientos Oculares/fisiología , Femenino , Haplorrinos , Humanos , Procesamiento de Imagen Asistido por Computador/métodos , Masculino , Neuronas/ultraestructura , Corteza Visual/anatomía & histología , Adulto Joven
7.
Cell Rep ; 42(11): 113341, 2023 11 28.
Artículo en Inglés | MEDLINE | ID: mdl-37897728

RESUMEN

Blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) of cortical layers relies on the hemodynamic response and is biased toward large veins on the cortical surface. Functional changes in the cerebral metabolic rate of oxygen (ΔCMRO2) may reflect neural cortical function better than BOLD fMRI, but it is unknown whether the calibrated BOLD model for functional CMRO2 measurement remains valid at high resolution. Here, we measure laminar ΔCMRO2 elicited by visual stimulation in macaque primary visual cortex (V1) and find that ΔCMRO2 peaks in the middle of the cortex, in agreement with autoradiographic measures of metabolism. ΔCMRO2 values in gray matter are similar as found previously. Reductions in CMRO2 are associated with veins at the cortical surface, suggesting that techniques for vein removal may improve the accuracy of the model at very high resolution. However, our results show feasibility of laminar ΔCMRO2 measurement, providing a physiologically meaningful metric of laminar functional metabolism.


Asunto(s)
Circulación Cerebrovascular , Corteza Visual , Animales , Circulación Cerebrovascular/fisiología , Imagen por Resonancia Magnética/métodos , Haplorrinos/metabolismo , Corteza Visual/fisiología , Oxígeno/metabolismo , Mapeo Encefálico/métodos , Encéfalo/metabolismo
8.
Cereb Circ Cogn Behav ; 5: 100189, 2023.
Artículo en Inglés | MEDLINE | ID: mdl-37941765

RESUMEN

Although dementia research has been dominated by Alzheimer's disease (AD), most dementia in older people is now recognised to be due to mixed pathologies, usually combining vascular and AD brain pathology. Vascular cognitive impairment (VCI), which encompasses vascular dementia (VaD) is the second most common type of dementia. Models of VCI have been delayed by limited understanding of the underlying aetiology and pathogenesis. This review by a multidisciplinary, diverse (in terms of sex, geography and career stage), cross-institute team provides a perspective on limitations to current VCI models and recommendations for improving translation and reproducibility. We discuss reproducibility, clinical features of VCI and corresponding assessments in models, human pathology, bioinformatics approaches, and data sharing. We offer recommendations for future research, particularly focusing on small vessel disease as a main underpinning disorder.

9.
Neuroimage ; 61(1): 98-105, 2012 May 15.
Artículo en Inglés | MEDLINE | ID: mdl-22426350

RESUMEN

In contrast to the limited use of functional magnetic resonance imaging (fMRI) in clinical diagnostics, it is currently a mainstay of neuroimaging in clinical and basic brain research. However, its non-invasive use in combination with its high temporal and spatial resolution would make fMRI a perfect diagnostic tool. We are interested in whether a pharmacological challenge imposed on the brain can be reliably traced by the blood oxygen level-dependent (BOLD) signal and possibly further exploited for diagnostics. We have chosen a systemic challenge with lactate and pyruvate to test whether the physiological formation of these monocarboxylic acids contributes to the BOLD signal and can be detected using fMRI. This information is also of interest because lactate levels in the cerebrospinal fluid rise concomitantly with reduced vascular responsiveness of the brain during the progression of Alzheimer disease (AD). We studied the BOLD response after a low-dose lactate challenge and monitored the induced plasma lactate levels in anesthetized non-human primates. We observed reliable lactate-induced BOLD responses, which could be confirmed at population and individual level by their strong correlation with systemic lactate concentrations. Comparable BOLD effects where observed after a slow infusion of pyruvate. We show here that physiological changes in lactate and pyruvate levels are indeed reflected in the BOLD signal, and describe the technical prerequisites to reliably trace a lactate challenge using BOLD-fMRI.


Asunto(s)
Química Encefálica/fisiología , Ácido Láctico/sangre , Corteza Visual/anatomía & histología , Corteza Visual/crecimiento & desarrollo , Envejecimiento/fisiología , Animales , Circulación Cerebrovascular/efectos de los fármacos , Circulación Cerebrovascular/fisiología , Interpretación Estadística de Datos , Fenómenos Electrofisiológicos , Femenino , Procesamiento de Imagen Asistido por Computador , Ácido Láctico/farmacología , Macaca mulatta , Imagen por Resonancia Magnética , Masculino , Microdiálisis , Oxígeno/sangre , Ácido Pirúvico/farmacología , Vasodilatación/efectos de los fármacos , Vasodilatación/fisiología
10.
Curr Biol ; 18(9): 631-40, 2008 May 06.
Artículo en Inglés | MEDLINE | ID: mdl-18439825

RESUMEN

BACKGROUND: Simultaneous intracortical recordings of neural activity and blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in primary visual cortex of anesthetized monkeys demonstrated varying degrees of correlation between fMRI signals and the different types of neural activity, such as local field potentials (LFPs), multiple-unit activity (MUA), and single-unit activity (SUA). One important question raised by the aforementioned investigation is whether the reported correlations also apply to alert subjects. RESULTS: Monkeys were trained to perform a fixation task while stimuli within the receptive field of each recording site were used to elicit neural responses followed by a BOLD response. We show -- also in alert behaving monkeys -- that although both LFP and MUA make significant contributions to the BOLD response, LFPs are better and more reliable predictors of the BOLD signal. Moreover, when MUA responses adapt but LFP remains unaffected, the BOLD signal remains unaltered. CONCLUSIONS: The persistent coupling of the BOLD signal to the field potential when LFP and MUA have different time evolutions suggests that BOLD is primarily determined by the local processing of inputs in a given cortical area. In the alert animal the largest portion of the BOLD signal's variance is explained by an LFP range (20-60 Hz) that is most likely related to neuromodulation. Finally, the similarity of the results in alert and anesthetized subjects indicates that at least in V1 anesthesia is not a confounding factor. This enables the comparison of human fMRI results with a plethora of electrophysiological results obtained in alert or anesthetized animals.


Asunto(s)
Potenciales Evocados Visuales/fisiología , Haplorrinos/fisiología , Imagen por Resonancia Magnética , Oxígeno/sangre , Corteza Visual/fisiología , Animales , Estado de Conciencia/fisiología , Fijación Ocular/fisiología
11.
Methods ; 50(3): 178-88, 2010 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-19683056

RESUMEN

In recent years, more and more laboratories have developed functional Magnetic Resonance Imaging (fMRI) for awake non-human primates. This research is essential to provide a link between non-invasive hemodynamic signals recorded in the human brain and the vast body of knowledge gained from invasive electrophysiological studies in monkeys. Given that their brain structure is so closely related to that of humans and that monkeys can be trained to perform complicated behavioral tasks, results obtained with monkey fMRI and electrophysiology can be compared to fMRI results obtained in humans, and provide information crucial to a better understanding of the mechanisms by which different cortical areas perform their functions in the human brain. However, despite that the first publications on fMRI in awake behaving macaques appeared approximately 10 years ago (Logothetis et al. (1999) [1], Stefanacci et al. (1998) [2], Dubowitz et al. (1998) [3]), relatively few laboratories perform such experiments routinely, a sign of the significant technical difficulties that must be overcome. The higher spatial resolution required because of the animal's smaller brain results in poorer signal-to-noise ratios than in human fMRI, which is further compounded by problems due to animal motion. Here, we discuss the specific challenges and benefits of fMRI in the awake monkey and review the methodologies and strategies for scanning behaving macaques.


Asunto(s)
Encéfalo/fisiología , Procesamiento de Imagen Asistido por Computador/métodos , Imagen por Resonancia Magnética/métodos , Animales , Conducta Animal/fisiología , Macaca mulatta , Modelos Animales , Movimiento/fisiología
12.
J Neurosci ; 28(46): 11796-801, 2008 Nov 12.
Artículo en Inglés | MEDLINE | ID: mdl-19005042

RESUMEN

The spatial organization of the brain's object and face representations in the temporal lobe is critical for understanding high-level vision and cognition but is poorly understood. Recently, exciting progress has been made using advanced imaging and physiology methods in humans and nonhuman primates, and the combination of such methods may be particularly powerful. Studies applying these methods help us to understand how neuronal activity, optical imaging, and functional magnetic resonance imaging signals are related within the temporal lobe, and to uncover the fine-grained and large-scale spatial organization of object and face representations in the primate brain.


Asunto(s)
Mapeo Encefálico/métodos , Reconocimiento Visual de Modelos/fisiología , Percepción Espacial/fisiología , Lóbulo Temporal/fisiología , Corteza Visual/fisiología , Mapeo Encefálico/instrumentación , Electrofisiología/métodos , Humanos , Imagen por Resonancia Magnética/métodos , Óptica y Fotónica/métodos , Lóbulo Temporal/anatomía & histología , Corteza Visual/anatomía & histología , Vías Visuales/anatomía & histología , Vías Visuales/fisiología
13.
J Cereb Blood Flow Metab ; 28(3): 640-52, 2008 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-17960143

RESUMEN

The blood oxygenation level-dependent (BOLD) signal is the most commonly used modality of functional magnetic resonance imaging (fMRI) today. Although easy to implement, it is an ambiguous signal since it results from a combination of several hemodynamic factors. Functional cerebral blood flow changes, as measured by using arterial spin labeling (ASL), typically occur in the parenchyma and have been demonstrated to be more closely coupled to neural activation compared with BOLD. However, the intrinsically low signals from ASL techniques have hindered its widespread application to fMRI for basic research and even more so for clinical applications. Here, we report the first implementation of continuous ASL in the anaesthetized macaque at high magnetic field of 7 T. The technique was optimized to permit maximum signal-to-noise ratio of functional perfusion-based images at high spatial resolution. The effect of labeling parameters, such as label time and post-label delay (PLD), on functional cerebral blood flow (fCBF) in the visual cortex was evaluated. Functional cerebral blood flow maps did not change with increasing label time after 2,000 ms, indicating that a label time of 2,000 ms is sufficient for reliable mapping of fCBF. The percent changes obtained using fCBF were better localized to gray matter, than those obtained with BOLD. A short PLD of 200 ms revealed significantly higher fCBF changes at the cortical surface, indicating large-vessel contamination, than a long PLD of 800 ms. However, the effect of the PLD on fCBF was smaller than on baseline CBF. These results are of importance for high-resolution applications, and when accurate quantification is required for studies in monkeys as well as in humans.


Asunto(s)
Mapeo Encefálico , Circulación Cerebrovascular , Angiografía por Resonancia Magnética/métodos , Imagen por Resonancia Magnética/métodos , Marcadores de Spin , Animales , Macaca , Primates , Flujo Sanguíneo Regional
14.
Neuron ; 99(6): 1107-1109, 2018 09 19.
Artículo en Inglés | MEDLINE | ID: mdl-30236280

RESUMEN

Memory encoding and retrieval require directional exchange of information between different areas in the medial temporal lobe. In this issue of Neuron, Koster et al. (2018) use high-resolution fMRI combined with state-of-the-art data analysis methods to trace the information flow in memory circuits in hippocampus and entorhinal cortex.


Asunto(s)
Mapeo Encefálico , Imagen por Resonancia Magnética , Hipocampo , Memoria , Lóbulo Temporal
15.
Curr Biol ; 28(2): 224-235.e5, 2018 01 22.
Artículo en Inglés | MEDLINE | ID: mdl-29307559

RESUMEN

Neural oscillations are ubiquitously observed in cortical activity, and are widely believed to be crucial for mediating transmission of information across the cortex. Yet, the neural phenomena contributing to each oscillation band, and their effect on information coding and transmission, are largely unknown. Here, we investigated whether individual frequency bands specifically reflect changes in the concentrations of dopamine, an important neuromodulator, and how dopamine affects oscillatory information processing. We recorded the local field potential (LFP) at different depths of primary visual cortex (V1) in anesthetized monkeys (Macaca mulatta) during spontaneous activity and during visual stimulation with Hollywood movie clips while pharmacologically mimicking dopaminergic neuromodulation by systemic injection of L-DOPA (a metabolic precursor of dopamine). We found that dopaminergic neuromodulation had marked effects on both spontaneous and movie-evoked neural activity. During spontaneous activity, dopaminergic neuromodulation increased the power of the LFP specifically in the [19-38 Hz] band, suggesting that the power of endogenous visual cortex oscillations in this band can be used as a robust marker of dopaminergic neuromodulation. Moreover, dopamine increased visual information encoding over all frequencies during movie stimulation. The information increase due to dopamine was prominent in the supragranular layers of cortex that project to higher cortical areas and in the gamma [50-100 Hz] band that has been previously implicated in mediating feedforward information transfer. These results thus individuate new neural mechanisms by which dopamine may promote the readout of relevant sensory information by strengthening the transmission of information from primary to higher areas.


Asunto(s)
Dopaminérgicos/farmacología , Dopamina/farmacología , Potenciales Evocados Visuales/fisiología , Macaca mulatta/fisiología , Corteza Visual/fisiología , Animales , Estimulación Luminosa
16.
Elife ; 72018 09 27.
Artículo en Inglés | MEDLINE | ID: mdl-30260771

RESUMEN

We examined alterations in E/I-balance in schizophrenia (ScZ) through measurements of resting-state gamma-band activity in participants meeting clinical high-risk (CHR) criteria (n = 88), 21 first episode (FEP) patients and 34 chronic ScZ-patients. Furthermore, MRS-data were obtained in CHR-participants and matched controls. Magnetoencephalographic (MEG) resting-state activity was examined at source level and MEG-data were correlated with neuropsychological scores and clinical symptoms. CHR-participants were characterized by increased 64-90 Hz power. In contrast, FEP- and ScZ-patients showed aberrant spectral power at both low- and high gamma-band frequencies. MRS-data showed a shift in E/I-balance toward increased excitation in CHR-participants, which correlated with increased occipital gamma-band power. Finally, neuropsychological deficits and clinical symptoms in FEP and ScZ-patients were correlated with reduced gamma band-activity, while elevated psychotic symptoms in the CHR group showed the opposite relationship. The current study suggests that resting-state gamma-band power and altered Glx/GABA ratio indicate changes in E/I-balance parameters across illness stages in ScZ.


Asunto(s)
Ritmo Gamma/fisiología , Inhibición Neural/fisiología , Descanso/fisiología , Esquizofrenia/fisiopatología , Adulto , Femenino , Humanos , Masculino , Factores de Riesgo , Índice de Severidad de la Enfermedad , Adulto Joven
17.
Magn Reson Imaging ; 25(6): 740-7, 2007 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-17499466

RESUMEN

To understand the physiological mechanisms underlying the blood-oxygenation-level-dependent (BOLD) signal, the acquisition of data must be optimized to achieve the maximum possible spatial resolution and specificity. The term "specificity" implies the selective enhancement of signals originating in the parenchyma, and thus best reflecting actual neural activity. Such spatial specificity is a prerequisite for imaging aimed at the elucidation of interactions between cortical micromodules, such as columns and laminae. In addition to the optimal selection of functional magnetic resonance imaging pulse sequences, accurate superposition of activation patterns onto corresponding anatomical scans, preferably acquired during the same experimental session, is necessary. At high resolution, exact functional-to-structural registration is of critical importance, because even small differences in geometry, that arise when different sequences are used for functional and anatomical scans, can lead to misallocation of activation and erroneous interpretation of data. In the present study, we used spin-echo (SE) echo planar imaging (EPI) for functional scans, since the SE-BOLD signal is sensitive to the capillary response, together with SE-EPI anatomical reference scans. The combination of these acquisition methods revealed a clear spatial colocalization of the largest fractional changes with the Gennari line, suggesting peak activity in Layer IV. Notably, this very same layer coincided with the largest relaxivity changes as observed in steady-state cerebral blood volume measurements, using the intravascular agent monocrystalline iron oxide nanoparticles (MION).


Asunto(s)
Imagen por Resonancia Magnética/métodos , Oxígeno/metabolismo , Algoritmos , Animales , Capilares , Circulación Cerebrovascular , Imagen Eco-Planar/métodos , Compuestos Férricos/farmacología , Óxido Ferrosoférrico/farmacología , Procesamiento de Imagen Asistido por Computador , Macaca , Nanopartículas , Flujo Sanguíneo Regional
18.
Neuron ; 96(6): 1253-1263.e7, 2017 12 20.
Artículo en Inglés | MEDLINE | ID: mdl-29224727

RESUMEN

Layer-dependent fMRI allows measurements of information flow in cortical circuits, as afferent and efferent connections terminate in different cortical layers. However, it is unknown to what level human fMRI is specific and sensitive enough to reveal directional functional activity across layers. To answer this question, we developed acquisition and analysis methods for blood-oxygen-level-dependent (BOLD) and cerebral-blood-volume (CBV)-based laminar fMRI and used these to discriminate four different tasks in the human motor cortex (M1). In agreement with anatomical data from animal studies, we found evidence for somatosensory and premotor input in superficial layers of M1 and for cortico-spinal motor output in deep layers. Laminar resting-state fMRI showed directional functional connectivity of M1 with somatosensory and premotor areas. Our findings demonstrate that CBV-fMRI can be used to investigate cortical activity in humans with unprecedented detail, allowing investigations of information flow between brain regions and outperforming conventional BOLD results that are often buried under vascular biases.


Asunto(s)
Mapeo Encefálico , Encéfalo/irrigación sanguínea , Circulación Cerebrovascular/fisiología , Corteza Motora/diagnóstico por imagen , Corteza Motora/fisiología , Oxígeno/sangre , Humanos , Procesamiento de Imagen Asistido por Computador , Imagen por Resonancia Magnética , Descanso
19.
Magn Reson Imaging ; 24(4): 381-92, 2006 May.
Artículo en Inglés | MEDLINE | ID: mdl-16677944

RESUMEN

The lamination of mammalian neocortex is widely used as reference for describing a wide range of anatomical and physiological data. Its value lies in the observation that in all examined species, cortical afferents, intrinsic cells and projection neurons organize themselves with respect to the laminae. The comprehension of the computations, carried out by the neocortical microcircuits, critically relies on the study of the interlaminar connectivity patterns and the intralaminar physiological processes in vivo. High-resolution functional neuroimaging, enabling the visualization of activity in individual cortical laminae or columns, may greatly contribute in such studies. Yet, the BOLD effect, as measured with the commonly used GE-EPI, contains contributions from both macroscopic venous blood vessels and capillaries. The low density of the cortical veins limits the effective spatial specificity of the fMRI signal and yields maps that are weighted toward the macrovasculature, which thus can be significantly different from the actual site of increased neuronal activity. Spin-echo (SE) sequences yielding apparent T2-weighted BOLD images have been shown to improve spatial specificity by increasing the sensitivity of the signal to spins of the parenchyma, particularly at high magnetic fields. Here we used SE-fMRI at 4.7 T to examine the specificity and resolution of functional maps obtained by stimulating the primary visual cortex of monkeys. Cortical layers could be clearly visualized, and functional activity was predominantly localized in cortical layer IV/Duvernoy layer 3. The choice of sequence parameters influences the fMRI signal, as the SE-EPI is by nature sensitive to T2* in addition to its T2 dependency. Using parameters that limit T2* effects yielded higher specificity and better visualization of the cortical laminae. Because the demands of high-spatial resolution using SE severely decreases temporal resolution, we used a stimulus protocol that allows sampling at higher effective temporal resolution. This way, it was possible to acquire high-spatial and high-temporal resolution SE-fMRI data.


Asunto(s)
Imagen por Resonancia Magnética , Corteza Visual/fisiología , Animales , Haplorrinos , Oxígeno/sangre , Sensibilidad y Especificidad
20.
Front Comput Neurosci ; 10: 66, 2016.
Artículo en Inglés | MEDLINE | ID: mdl-27445782

RESUMEN

As high-resolution functional magnetic resonance imaging (fMRI) and fMRI of cortical layers become more widely used, the question how well high-resolution fMRI signals reflect the underlying neural processing, and how to interpret laminar fMRI data becomes more and more relevant. High-resolution fMRI has shown laminar differences in cerebral blood flow (CBF), volume (CBV), and neurovascular coupling. Features and processes that were previously lumped into a single voxel become spatially distinct at high resolution. These features can be vascular compartments such as veins, arteries, and capillaries, or cortical layers and columns, which can have differences in metabolism. Mesoscopic models of the blood oxygenation level dependent (BOLD) response therefore need to be expanded, for instance, to incorporate laminar differences in the coupling between neural activity, metabolism and the hemodynamic response. Here we discuss biological and methodological factors that affect the modeling and interpretation of high-resolution fMRI data. We also illustrate with examples from neuropharmacology and the negative BOLD response how combining BOLD with CBF- and CBV-based fMRI methods can provide additional information about neurovascular coupling, and can aid modeling and interpretation of high-resolution fMRI.

SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA