Cortical origin of middle-latency auditory evoked responses in man.

We have recorded middle-latency magnetic evoked responses to 50-ms noise bursts, presented once every 0.9 s, over the right hemisphere of healthy humans. The measurements were carried out with a sensitive 7-channel SQUID gradiometer with a passband of 0.5-2000 Hz. The response consisted of peaks at about 30, 50 and 65 ms. The location of the equivalent source of the 30-ms deflection agrees with activation of the supratemporal auditory cortex, slightly anterior to the source area of the well-known 100-ms deflection.