EFFECTS OF INTENSITY VARIATION ON HUMAN AUDITORY-EVOKED MAGNETIC-FIELDS

We recorded auditory evoked magnetic fields from 6 healthy subjects wi th a 122-channel whole-head neuromagnetometer. The stimuli were 200-ms 1-kHz tones delivered at 4 different intensities (40, 50, 60, and 65 dB HL). The tones were given once every second, binaurally in the firs t session, and monaurally to each ear in the second one. The four inte nsities were presented randomly and equiprobably within a single seque nce. In both stimulus conditions, the 100-ms response (N100m) decrease d in latency and increased in amplitude as a function of intensity in both hemispheres. No systematic dependence was found between stimulus intensity and the N100m source location in the auditory cortex. Our st udy illustrates a noninvasive method to examine the functional propert ies of human auditory cortex, allowing simultaneous comparison between signals arising from both hemispheres.