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Axon Hillock Currents Allow Single-Neuron-Resolution 3-Dimensional Functional Neural Imaging Using Diamond Quantum Defect-Based Vector Magnetometry

Magnetic field sensing, with its recent advances, is emerging as a viable alternative to measure functional activity of single neurons in the brain by sensing action potential associated magnetic fields (APMFs). Measurement of APMFs of large axons of worms have been possible due to their size. In the mammalian brain, axon sizes, their numbers and routes, restricts using such functional imaging methods. With segmented model of mammalian pyramidal neurons, we show that the APMF of intra-axonal currents in the axon hillock are two orders of magnitude larger than other neuronal locations. Expected 2-dimensional vector magnetic field maps of naturalistic spiking activity of a volume of neurons via widefield diamond-nitrogen-vacancy-center-magnetometry (DNVM) were simulated. A dictionary based matching pursuit type algorithm applied to the data using the axon-hillock's APMF signature allowed spatiotemporal reconstruction of APs in the volume of brain tissue at single cell resolution. Enhancement of APMF signals coupled with NVMM advances thus can potentially replace current functional brain mapping techniques.