Dependence of the auditory evoked magnetic field (100 msec signal) of the human brain on the intensity of the stimulus.

ABSTRACT

The intensity dependence of the 100 msec magnetic field signal evoked by contralateral application of a tone burst stimulus has been examined for both hemispheres and for a number of frequencies. In all cases the component of the magnetic field normal to the skull was measured; in some cases this component was oriented in the outward direction (group 1 and some group 2 subjects), in the other cases in the inward direction (group 2). The experimental results were analysed in terms of an equivalent current dipole model. The analysis gave rise to the introduction of a transit time (tau 0 approximately 60 msec) from the onset of the stimulus to the activation of the current dipole and to the introduction of a functional relationship between the dipole moment and a 'reduced' intensity, and between the latency and the 'reduced' intensity. Further, the reproducibility of the signal was verified.