title: Inhibition of auditory cortical responses to ipsilateral stimuli during dichotic listening: evidence from magnetoencephalography.
abstract: 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.
authors.affiliation: Dipartimento di Fisiologia Umana e Farmacologia, Università La Sapienza, P.le Aldo Moro 5, 00185-Roma, Italy.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Brancucci
authors.forename: Claudio
authors.initials: C
authors.lastname: Babiloni
authors.forename: Fabio
authors.initials: F
authors.lastname: Babiloni
authors.forename: Silvana
authors.initials: S
authors.lastname: Galderisi
authors.forename: Armida
authors.initials: A
authors.lastname: Mucci
authors.forename: Franca
authors.initials: F
authors.lastname: Tecchio
authors.forename: Filippo
authors.initials: F
authors.lastname: Zappasodi
authors.forename: Vittorio
authors.initials: V
authors.lastname: Pizzella
authors.forename: Gian Luca
authors.initials: GL
authors.lastname: Romani
authors.forename: Paolo Maria
authors.initials: PM
authors.lastname: Rossini
mesh_terms: 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*