Direct neural current imaging in an intact cerebellum with magnetic resonance imaging

Abstract

The ability to detect neuronal currents with high spatiotemporal resolution using magnetic resonance imaging (MRI) is important for studying human brain function in both health and disease. While significant progress has been made, we still lack evidence showing that it is possible to measure an MR signal time-locked to neuronal currents with a temporal waveform matching concurrently recorded local field potentials (LFPs). Also lacking is evidence that such MR data can be used to image current distribution in active tissue. Since these two results are lacking even in vitro, we obtained these data in an intact isolated whole cerebellum of turtle during slow neuronal activity mediated by metabotropic glutamate receptors using a gradient-echo EPI sequence (TR = 100 ms) at 4.7 T. Our results show that it is possible (1) to reliably detect an MR phase shift time course matching that of the concurrently measured LFP evoked by stimulation of a cerebellar peduncle, (2) to detect the signal in single voxels of 0.1 mm3, (3) to determine the spatial phase map matching the magnetic field distribution predicted by the LFP map, (4) to estimate the distribution of neuronal current in the active tissue from a group-average phase map, and (5) to provide a quantitatively accurate theoretical account of the measured phase shifts. The peak values of the detected MR phase shifts were 0.27–0.37°, corresponding to local magnetic field changes of 0.67–0.93 nT (for TE = 26 ms). Our work provides an empirical basis for future extensions to in vivo imaging of neuronal currents.

Local recording of biological magnetic fields using Giant Magneto Resistance-based micro-probes

“…but comparable to that measured in worm with NV centers in diamond5. A 3 nT amplitude is just above the upper bound of the predictions2627 and the estimates2829 for the central nervous system, i.e. 0.1 to 1 nT.…”

Direct detection of neural activity in vitro using magnetic resonance electrical impedance tomography (MREIT)

“…Many methods have sought to directly image neural activity in vivo using magnetic resonance methods. These include the area of neural current magnetic resonance imaging (ncMRI), where disturbances in the main magnetic field of an MR system caused by intrinsic neural currents have been observed to produce artifacts in magnitude or phase images (Bandettini et al, 2005; Huang, 2014; Huang and Zhu, 2015; Jiang et al, 2014; Luo and Gao, 2009; Park et al, 2006; Petridou et al, 2006; Sundaram et al, 2016). More recently, attempts have been made to detect the effects of ion flow using Lorentz force imaging (Pourtaheri et al, 2013; Truong et al, 2008) and Mg enhanced MR imaging (Radecki et al, 2014).…”

Solving High-Resolution Forward Problems for Extra- and Intracranial Neurophysiological Recordings Using Boundary Element Fast Multipole Method

“…The Okada-Murakami constant of 0 = 1 nA • m mm 2 ⁄ (Murakami & Okada, 2006;Murakami & Okada, 2015), also confirmed in a recent MRI study (Sundaram et al, 2016), is used to obtain a realistic current dipole density across the source region. When the dipole length is and the area of the dipole layer is , an expression for the dipole current 0 follows from 0 = 0 ⁄ , which yields 0 = 0 ⁄ .…”