Detection and measurement of steady-state evoked potentials in real-time using a lock-in amplifier. Technical note

A system for recording evoked potentials, in which a lock-in amplifier replaces the averaging computer, is described. With this system, the set-up is much the same as in the conventional apparatus, with the following exceptions: 1) the amplifier gain is set at only a few thousands; 2) analogue-to-digital conversion and computer averaging is replaced by a lock-in amplifier; and 3) the output of the system is an analogue signal representing the amplitude of the recorded steady-state evoked potentials and the phase of baseline crossings. This set-up is much less costly than the conventional apparatus, much easier to operate, and, with its real-time output, may provide an ideal technique for screening and monitoring purposes.