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Auditory evoked magnetic fields: response amplitude vs. stimulus intensity



Auditory evoked magnetic fields: response amplitude vs. stimulus intensity



Electroencephalography and Clinical Neurophysiology 54(2): 147-152



Auditory evoked magnetic fields (AEF) and EEG auditory evoked potentials (AEP) were recorded from the right hemisphere of 24 normal subjects. MEG [magnetoencephalogram] and EEG recordings were made from a point 1/4 of the distance from T[throax]4 to C[cervical]4, in response to contralateral ear stimulaton by irregularly spaced 100 ms long 1 kHz tone bursts at 40, 60, 80 and 100 dB sound pressure level (SPL). A figure-8 SQUID [superconducting quantum interference device] gradiometer was used for magnetic recordings. MEG and EEG, bandpassed between 2-40 Hz, were averaged for 500 ms following 128 stimuli. A mean response was computed for the group of 24 subjects at each stimulus intensity, and the integrated area under the curve of this mean response for the 1st 200 ms was obtained. The amplitudes of the largest responses occurring within the first 250 ms after stimulus delivery were also measured, as was the amplitude of a biological noise (no stimulus) control. The amplitude of AEF increased rapidly to .apprx. 60% of maximum at 60 dB SPL, with the field amplitudes produced by 60, 80 and 100 dB stimuli tending to plateau or even decrease slightly. The amplitude of the simultaneously recorded AEP increased linearly with increasing stimulus intensity. The plateau effect or decrease of the AEF amplitude with increasing stimulus intensity may be caused by an inward movement of the current dipole with increasing stimulus intensity and/or may reflect primarily local intracellular currents associated with single unit activation patterns in auditory cortical regions, whereas AEP may reflect more widespread extracellular currents.

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Accession: 004798219

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PMID: 6179739

DOI: 10.1016/0013-4694(82)90156-0


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