Interhemispheric asymmetry of tone stimuli processing in 5- 6-year-old children : an AEP topographic study

Bruneau, N., Vidal, J., Gomot, M., Roux, S., and Barthélémy, C.
Departement of Neurophysiology in Child Psychiatry, Inserm U316, Tours Hospital, France

Late auditory evoked response recorded at fronto-central sites in young children is constituted of a positive wave culminating at around 100 ms followed by a negative wave culminating at around 250 ms. Topographical analyses (scalp potentials and scalp current density mapping) of these responses were performed according to ear of stimulation. Fifteen right-handed children (8 girls) aged from 5 years to 6 years (mean ± sem : 5yrs 8mths ± 2 mths) participated in the study. Auditory stimulations were monaural tones (1100 Hz, 70 dBSPL, 50 ms duration) delivered at four different interstimulus intervals (700, 1100, 1500, 3000 ms). Both P100 and N250 waves involved generators in the supratemporal cortex as indicated by bilateral sink/source currents localized at infero-temporal sites. The orientation of these sink/source complexes were opposite for P100 and N250. Amplitude of currents decreased for P100 and increased for N250 when rate of stimulation increased. For both waves amplitude of temporal currents were significantly greater on the left hemisphere and greater for contralateral than for ipsilateral ear stimulation. On the right hemisphere responses were of smaller amplitude and did not differ according to the ear stimulated. Left lateralized brain activation were previously demonstrated in response to speech stimuli both in infants and in children. Our results therefore indicated a left-lateralized brain activation also for tone-stimuli.