RELATIONSHIP OF TRANSIENT AND STEADY-STATE AUDITORY-EVOKED FIELDS

Transient and steady-state auditory evoked fields (AEFs) to brief tone pips were recorded over the left hemisphere at 7 different stimulus r ates (0.125-39 Hz) using a 37-channel biomagnetometer. Previous observ ations of transient auditory gamma band response (GBR) activity were r eplicated. Similar rate characteristics and equivalent dipole location s supported the suggestion that the steady-state response (SSR) at abo ut 40 Hz represents the summation of successive overlapping (10 Hz) mi ddle latency responses (MLRs). On the other hand, differences in equiv alent dipole locations and habituation effects suggest that the magnet ically recorded GBR is a separate phenomenon which occurs primarily at low stimulus rates and is unrelated to either the magnetically record ed MRL or SSR.