Differential characteristics of the middle latency auditory evoked magnetic responses to interstimulus intervals.
OBJECTIVE
The human middle latency auditory evoked magnetic fields were recorded with different interstimulus intervals (ISI) to investigate the differential natures of P30m and the P50m, including whether the P50m source was spatially different or not from the P30m source.


METHODS
Twenty right-handed healthy subjects participated in the experiment. Auditory magnetic responses were recorded in the 0.5 s ISI (ISI were between 0.4 and 0.6 s) and the 1.5 s ISI conditions (ISI were between 1 and 2 s). Tone bursts were presented to the right ears 880 times consecutively for each condition. The P30m and the P50m responses were investigated, and the dipole source localization was performed.


RESULTS
The P50m latency was significantly prolonged, while the P30m latency did not vary in the shorter ISI. Both P50m and P30m amplitudes were significantly reduced in the shorter ISI. The P50m was located significantly more anteriorly than P30m.


CONCLUSIONS
These results suggest the existence of differential characteristic and spatially different magnetic responses in the middle latency range.


CONCLUSIONS
This study has revealed one aspect of the different natures between P30m and P50m, and may provide a key for auditory perceptional processes in humans.
Onitsuka
Toshiaki
T
Department of Neuropsychiatry, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. toshi@bwh.harvard.edu
Ninomiya
Hideaki
H
Sato
Eigo
E
Yamamoto
Tomoya
T
Tashiro
Nobutada
N
D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001303:Auditory Cortex; D001931:Brain Mapping; D004569:Electroencephalography / Q000295:instrumentation / Q000379:methods; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D008297:Male; D011930:Reaction Time / Q000502:physiology*; D013017:Sound Localization; D013997:Time Factors