Improved instrumentation for measuring the magnetic field of cellular action currents

Abstract

The instrumentation for measuring the magnetic field associated with the action potential in isolated nerve bundles has been improved to the extent that measurements can now be made in a typical laboratory without magnetic shielding. The superconducting magnetometer is operated in a liquid‐helium storage Dewar so that transfers of liquid helium are no longer required. A power‐line trigger circuit is used to minimize the interference of 60 Hz noise and its odd harmonics. A compensation circuit has been developed to correct, in real time, for the high‐pass characteristics of the magnetometer. As a result of these improvements, it is possible to observe action currents as small as 0.1 μA in a 1.0‐Hz to 1‐kHz bandwidth without signal averaging.