Hyperpolarizationactivated

Hyperpolarization is a term used in multiple disciplines. In physiology, it refers to the change of a cell’s membrane potential toward more negative values, typically following an action potential or inhibitory synaptic input. This increase in the magnitude of the membrane potential makes it less likely that the neuron will fire again immediately. In physics and chemistry, hyperpolarization describes a nonthermal excess of population in certain spin states, which yields greatly amplified signals in magnetic resonance techniques such as NMR and MRI.

In spin physics, hyperpolarization methods include dynamic nuclear polarization (DNP), which transfers polarization from electron spins to nuclei using microwave irradiation at low temperatures; spin-exchange optical pumping (SEOP), which uses polarized alkali atoms to polarize noble gas nuclei; para-hydrogen induced polarization (PHIP) and its variant SABRE, which transfer symmetry-converted hydrogen spin order to target molecules. The Overhauser effect is another mechanism applicable to liquids. These methods can boost NMR/MRI signal by up to several orders of magnitude, enabling in vivo imaging with hyperpolarized tracers.

Applications include medical imaging using hyperpolarized carbon-13 compounds such as pyruvate or bicarbonate for metabolic and physiologic studies, real-time monitoring of tumor metabolism, and materials science for studying chemical reactions and transport. While hyperpolarization greatly enhances sensitivity, the hyperpolarized state decays with a characteristic relaxation time, requiring rapid data acquisition.

Within neuroscience, hyperpolarization of neurons occurs when membrane potential becomes more negative than the resting level, suppressing excitability and shifting conductance; it is typically produced by the opening of potassium channels or chloride influx and underlies inhibitory synaptic signaling.