Binaural interactions in the short-latency evoked potentials of neonates

Short-latency evoked potentials to monaural and binaural clicks were recorded from scalp electrodes on healthy full-term neonates and on normally hearing adults. Binaural interaction (BI) was measured by summing the average monaural responses obtained from each ear (L+R) and subtracting the binaural response (B) from the monaural sum (BI=L+R-B). Consistent BI was apparent following stimulation with moderate level clicks in all cooperative infants. As in the adult, BI occurred during waves IV, V and VI, where there were systematic amplitude differences between the L+R and B waveforms. Peak latencies of the waves were not significantly affected. However, peak latencies were longer in neonates than in adults, reflecting maturational changes in the response. Similarly, peak latencies in the BI waveforms were also prolonged for the neonates. These results indicate that: (1) BI is present at or soon after birth; (2) the gross response properties of BI are similar in infants and adults; (3) BI occurs during specific waves in the response, independent of age, and (4) the assessment of BI may prove useful in estimating the functional integrity of brain stem structures in infants.