In vivo magnetic recording of single-neuron action potentials

Measuring fast neuronal signals is the domain of electrophysiology and magnetophysiology. Although electrophysiology is easier to perform, magnetophysiology avoids tissue-based distortions and measures a signal with directional information. At the macroscale, magnetoencephalography (MEG) is established, and at the mesoscale, visually evoked magnetic fields have been reported. At the microscale however, while benefits of recording magnetic counterparts of electric spikes would be numerous, they are also highly challenging in vivo. Here, we combine magnetic and electric recordings of neuronal action potentials in anesthetized, male rats using miniaturized giant magnetoresistance (GMR) sensors. We reveal the magnetic signature of action potentials of well-isolated single units. The recorded magnetic signals showed a distinct waveform and considerable signal strength. This demonstration of in vivo magnetic action potentials opens a wide field of possibilities to profit from the combined power of magnetic and electric recordings and thus to significantly advance the understanding of neuronal circuits.<b>NEW & NOTEWORTHY</b> Electrophysiological tools allow the measurement of single-neuron action potentials with high temporal resolution. Magnetophysiological measurements add valuable information but are hard to achieve for single neurons. Established technology for noninvasive magnetic measurements cannot be used in vivo. We demonstrate that miniaturized giant magnetoresistance sensors enable measuring magnetic counterparts of action potentials in vivo. This proof-of-principle shows a way toward integrating magnetic and electric recordings to profit from the complementary information measured by each modality.