Inhibition of auditory cortical responses to ipsilateral stimuli during dichotic listening: evidence from magnetoencephalography.
The present magnetoencephalography (MEG) study on auditory evoked magnetic fields (AEFs) was aimed at verifying whether during dichotic listening the contralateral auditory pathway inhibits the ipsilateral one, as suggested by behavioural and patient studies. Ten healthy subjects were given a randomized series of three complex tones (261, 293 and 391 Hz, 500 ms duration), which were delivered monotically and dichotically with different intensities [60, 70 or 80 dBA (audio decibels)]. MEG data were recorded from the right auditory cortex. Results showed that the M100 amplitude over the right auditory cortex increased progressively when tones of increasing intensity were provided at the ipsilateral (right) ear. This effect on M100 was abolished when a concurrent tone of constant intensity was delivered dichotically at the contralateral (left) ear, suggesting that the contralateral pathway inhibited the ipsilateral one. The ipsilateral inhibition was present only when the contralateral tone fundamental frequency was similar to the ipsilateral tone. It was proposed that the occlusion mechanism would be exerted in cortical auditory areas as the dichotic effects were observed at M100 but not M50 component. This is the first evidence showing a neurophysiological inhibition driven by the contralateral auditory pathway over the ipsilateral one during dichotic listening.
Brancucci
Alfredo
A
Dipartimento di Fisiologia Umana e Farmacologia, Università La Sapienza, P.le Aldo Moro 5, 00185-Roma, Italy.
Babiloni
Claudio
C
Babiloni
Fabio
F
Galderisi
Silvana
S
Mucci
Armida
A
Tecchio
Franca
F
Zappasodi
Filippo
F
Pizzella
Vittorio
V
Romani
Gian Luca
GL
Rossini
Paolo Maria
PM
D000161:Acoustic Stimulation / Q000379:methods; D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D004007:Dichotic Listening Tests / Q000379:methods*; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*