Side of the stimulated ear influences the hemispheric balance in coding tonal stimuli.
OBJECTIVE
To evaluate whether the side of stimulated ear affects the hemispheric asymmetry of auditory evoked cortical activations.


METHODS
Using a whole-head neuromagnetometer, we recorded neuromagnetic approximately 100 ms responses (N100m) in 21 healthy right-handers to 100 ms 1 kHz tones delivered alternatively to left and right ear.


RESULTS
Although the peak latencies of N100m were shorter in contralateral than in ipsilateral hemisphere, the difference was significant only for the left ear stimulation. Based on the relative N100m amplitudes across hemispheres, the laterality evaluation showed a rightward predominance of N100m activation to tone stimuli, but the lateralization toward the right hemisphere was more apparent by the left than by the right ear stimulation (laterality index: -0.27 versus -0.10, p=0.008). Within the right hemisphere, the N100m was 2-4 mm more posterior for left ear than for right ear stimulation.


CONCLUSIONS
The hemispheric asymmetry in auditory processing depends on the side of the stimulated ear. The more anterior localization of right N100m responses to ipsilateral than to contralateral ear stimulation suggests that there might be differential neuronal populations in the right hemisphere for processing spatially different auditory inputs.
Yu
Hsiang-Yu
HY
Department of Neurology, National Yang-Ming University, Taipei, Taiwan.
Chen
Jen-Tse
JT
Wu
Zin-An
ZA
Yeh
Tzu-Chen
TC
Ho
Low-Tone
LT
Lin
Yung-Yang
YY
D000161:Acoustic Stimulation / Q000379:methods; D000293:Adolescent; D000328:Adult; D001301:Audiometry, Pure-Tone / Q000379:methods; D001307:Auditory Perception / Q000502:physiology*; D001931:Brain Mapping; D004292:Dominance, Cerebral / Q000502:physiology / Q000528:radiation effects*; D004423:Ear / Q000528:radiation effects; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D011930:Reaction Time / Q000502:physiology