In Vivo Magnetic Recording of Neuronal Activity

“The detection of weak fields from the body is a technological triumph. The field strength from lung particles is about 10–9T [Tesla]; from the heart it is about 10–10T; from the brain it is 10–12T for spontaneous (α-wave) activity and 10–13T for evoked responses. These signals must be compared to 10–4T for the earth’s magnetic field. Noise due to spontaneous changes in the earth’s field can be as high as 10–7T. Noise due to power lines, machinery, and the like can be 10–5– 10–4T.”

Abstract: Neuronal activity generates ionic flows and thereby both magnetic fields and electric potential differences, i.e., voltages. Voltage measurements are widely used but suffer from isolating and smearing properties of tissue between source and sensor, are blind to ionic flow direction, and reflect the difference between two electrodes, complicating interpretation. Magnetic field measurements could overcome these limitations but have been essentially limited to magnetoencephalography (MEG), using centimeter-sized, helium-cooled extracranial sensors. Here, we report on in vivo magnetic recordings of neuronal activity from visual cortex of cats with magnetrodes , specially developed needle-shaped probes carrying micron-sized, non-cooled magnetic sensors based on spin electronics. Event-related magnetic fields inside the neuropil were on the order of several nanoteslas, informing MEG source models and efforts for magnetic field measurements through MRI. Though the signal-to-noise ratio is still inferior to electrophysiology, this proof of concept demonstrates the potential to exploit the fundamental advantages of magnetophysiology.

A Magnetrode. Adapted from Fig. 1a in Caruso et al. (2017) Neuron 95:1283–1291.

“Implanted recording probes play an important role in many neurotechnological scenarios. Untethered probes are particularly intriguing, as they avoid connection wires and corresponding limitations.”



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