Investigation of MR signal modulation due to magnetic fields from neuronal currents in the adult human optic nerve and visual cortex

Chow, Li Sze; Cook, G.G.; Whitby, Elspeth; Paley, Martyn N.J.

doi:10.1016/j.mri.2006.01.005

Cited by 30 publications

(52 citation statements)

References 13 publications

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“…However, using a detection threshold (0.2%) smaller than these signal changes, no ncMRI activation was detected in the present study without the task-induced BOLD activation. This suggests that the signal changes observed in the previous ncMRI studies (2,3,7,8,10) cannot be confidently attributed to the direct effect of neuronal currents. They may result from the contamination of the task-induced BOLD background.…”

Section: Discussionmentioning

confidence: 85%

“…Therefore, both of these BOLD artifact-free human and animal studies indicate that the ncMRI signal evoked by the physiological (visual) stimulation is too weak to be detected. In the previous ncMRI studies on human subjects (2,3,7,8,10), fast signal changes of $0.3-1% were observed in the magnitude images using steady-state stimulation tasks. However, using a detection threshold (0.2%) smaller than these signal changes, no ncMRI activation was detected in the present study without the task-induced BOLD activation.…”

Section: Discussionmentioning

confidence: 87%

“…Nonetheless, up to date, a consensus has not been reached on the detectability of ncMRI on human subjects. Multiple groups have reported a successful detection of ncMRI signal in human brain (2)(3)(4)(5)(6)(7)(8)(9)(10), while a failure in ncMRI detection has been claimed in other studies (11)(12)(13)(14)(15). Due to these conflicting results, there is still no conclusion on the question whether ncMRI signal is detectable or not.…”

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confidence: 98%

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Detection of neuronal current MRI in human without BOLD contamination

Luo

Jiang

Gao

2011

Magnetic Resonance in Med

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Controversial results regarding the detectability of neuronal current magnetic resonance imaging (ncMRI) have been reported in different studies on human subjects. In all the previous studies, the ncMRI signal was detected under a continuous and paradigm task-induced blood oxygen level dependent (BOLD) signal background. The aim of this study is to investigate the possibility of detecting ncMRI signal in human brain in the situation that task-induced BOLD background is absent or minimum. In this study, by adopting an event-related visuomotor paradigm with long interstimulus interval (520 s), the ncMRI signal was detected when the BOLD signal fully returned to its baseline, and the potential BOLD background contamination was avoided effectively. The results showed that the visuomotor stimulation elicited BOLD activation in visual and motor cortices, but no significant ncMRI signal change (in magnitude) was detected in human brain. These experimental findings are consistent with theoretical predications. Magn Reson Med 66:492-497,

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Section: Discussionmentioning

confidence: 85%

Section: Discussionmentioning

confidence: 87%

mentioning

confidence: 98%

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Detection of neuronal current MRI in human without BOLD contamination

Luo

Jiang

Gao

2011

Magnetic Resonance in Med

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“…Several studies have explored the feasibility of using MRI for detecting the minute magnetic field changes induced by electrical currents in phantoms (1)(2)(3) or by neuronal currents in human subjects (4)(5)(6)(7)(8)(9)(10)(11)(12)(13), thereby combining the high temporal resolution of electrical and magnetic recording methods with the high spatial resolution and noninvasiveness inherent in MRI. Despite some encouraging results in phantoms, the direct imaging of neural activation in vivo has been challenging because of the small activation-induced magnetic field changes and because of multiple, synchronized, confounding signals in the brain reflecting cerebral blood oxygenation, blood volume, and blood flow changes or physiological noise (6,9).…”

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confidence: 99%

Finding neuroelectric activity under magnetic-field oscillations (NAMO) with magnetic resonance imaging in vivo

Truong

Song

2006

Proc. Natl. Acad. Sci. U.S.A.

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Neuroimaging techniques are among the most important tools for investigating the function of the human nervous system and for improving the clinical diagnosis of neurological disorders. However, most commonly used techniques are limited by their invasiveness or their inability to accurately localize neural activity in space or time. Previous attempts at using MRI to directly image neuroelectric activity in vivo through the detection of magnetic field changes induced by neuronal currents have been challenging because of the extremely small signal changes and confounding factors such as hemodynamic modulations. Here we describe an MRI technique that uses oscillating magnetic field gradients to significantly amplify and detect the Lorentz effect induced by neuroelectric activity, and we demonstrate its effectiveness in imaging sensory nerve activation in vivo in the human median nerve during electrical stimulation of the wrist. This direct, realtime, and noninvasive neuroimaging technique may potentially find broad applications in neurosciences.Lorentz effect ͉ median nerve ͉ neuroimaging ͉ MRI T he ongoing pursuit to better detect neural activity has led to many exciting technical advances over the past decades, including single-cell electrical recordings, electroencephalography (EEG), magnetoencephalography (MEG), positron emission tomography (PET), and, more recently, functional magnetic resonance imaging (fMRI). To date, neuroimaging techniques are invasive (single-cell recordings) and͞or limited in their ability to accurately localize neural activity in space (EEG, MEG) or in time (PET, fMRI). Even when information is combined across multiple modalities, there remain fundamental limitations that introduce sources of error and interpretative difficulties. It is therefore time to develop novel techniques that allow noninvasive imaging of neural activity with a high accuracy both spatially and temporally.Several studies have explored the feasibility of using MRI for detecting the minute magnetic field changes induced by electrical currents in phantoms (1-3) or by neuronal currents in human subjects (4-13), thereby combining the high temporal resolution of electrical and magnetic recording methods with the high spatial resolution and noninvasiveness inherent in MRI. Despite some encouraging results in phantoms, the direct imaging of neural activation in vivo has been challenging because of the small activation-induced magnetic field changes and because of multiple, synchronized, confounding signals in the brain reflecting cerebral blood oxygenation, blood volume, and blood flow changes or physiological noise (6, 9). Here we seek to address these two fundamental issues and to demonstrate the potential capability of MRI to directly image neuroelectric activity in vivo.First, to boost the signal detectability, we propose an acquisition strategy based on the Lorentz effect induced by neuroelectric activity. The contrast mechanism of Lorentz effect imaging was initially validated in phantoms with a proof-ofconcept puls...

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“…One possible reason for the discrepancy between these results is that Parkes et al used an inter-stimulus interval (ISI) of one second, while Xiong et al used two seconds, and two seconds may allow small BOLD signals to occur (Parkes et al, 2007). Other nc-MRI experiments have reported no signal change (Chu et al, 2004), small changes in the signal magnitude (Liston et al, 2004;Chow et al, 2006), or small changes in the signal phase (Bianciardi et al, 2004). Shown are the sizes of the activated area of four brain regions: V1, M1, S1, and SMA.…”

Section: Nc-mri Experimentsmentioning

confidence: 98%

Realistic models for detection of neuronal currents with magnetic resonance imaging

Du¹

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A great challenge facing brain research is to "see" neurons in action at high spatial and temporal resolution in the living human brain. While existing non-invasive techniques, such as electroencephalography (EEG), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI), have either poor spatial or temporal resolution, neuronal current MRI (nc-MRI) may hold the potential to revolutionize cognitive neuroscience by imaging neuronal activity at high temporal and spatial resolutions.However, the implementation of nc-MRI using existing instrumentation is yet to be convincingly demonstrated.In this project, I investigated the feasibility of nc-MRI via computer simulations. To allow realistic neuronal current simulations, the laminar cortex model (LCM) was first developed.The LCM incorporates the laminar architecture of the cerebral cortex into a continuum cortex model (previously developed by Wright et al.) to simulate the collective activity of cortical neurons. As validations, the LCM has been used to simulate the local field potentials (LFP) of the primary visual cortex. The LCM produced spontaneous LFPs exhibited frequency-inverse (1/f) power spectrum behaviour. The LCM also captured the fundamental as well as the high order harmonics under intermittent light stimulation.To model neuronal currents, I decomposed the neuronal activity simulated by the LCM into action potentials and postsynaptic potentials. The geometries of dendrites and axons were generated dynamically to account for neuronal morphology diversity. Magnetic fields produced by action potentials and postsynaptic potentials were calculated for the cases of spontaneous and stimulated cortical activity, from which the nc-MRI signal was determined. The MRI signal magnitude change was found to be below currently detectable levels (< 0.1 part-per-million), but signal phase change was potentially detectable (in the order of 0.1 milli-radian). Furthermore, nc-MRI signals were sensitive to temporal and spatial variations in neuronal activity and independent of the intensity of neuronal activation. Synchronous neuronal activity produces large phase changes, up to 1 milliradian, and the signal phase oscillated with neuronal activity.Based on the computer simulation results, I proposed to image oscillatory neuronal currents using a multi-echo spin echo (MESE) and a synchronised multi-echo gradient recalled echo (MEGRE) sequences. A MESE sequence can accumulate phase changes for multiple neuronal activity oscillation periods through applying radio-frequency (RF) -Iexcitation pulses at the times when neuronal magnetic fields change sign. MEGRE sequence could be used to extract neuronal current signal from noisy MRI signals, because neuronal current signal but not blood-oxygen-level dependent (BOLD) effect or noise, varies with neuronal oscillation. Because a MEGRE sequence is capable of acquiring MRI signals at a series of closely-spaced time points, the inherent oscillation of neuronal current signals may potentially be deduced from ...

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Investigation of MR signal modulation due to magnetic fields from neuronal currents in the adult human optic nerve and visual cortex

Cited by 30 publications

References 13 publications

Detection of neuronal current MRI in human without BOLD contamination

Detection of neuronal current MRI in human without BOLD contamination

Finding neuroelectric activity under magnetic-field oscillations (NAMO) with magnetic resonance imaging in vivo

Realistic models for detection of neuronal currents with magnetic resonance imaging

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