Intensity effect on latency and interval of human BAER

Binaural interaction and the effects of stimulus intensity and repetition rate in human auditory brain-stem

Binaural interaction (BI) components in brain-stem auditory evoked potential (BAEP) and their changes with stimulus intensity and repetition rate were examined in human adult. Seven BI components were identified, which occurred between the latency range of 5 and 11 ms and coincided consistently with the latency range of BAEP waves IV-VII. Waves DV and DVII, occurring at the downslopes of BAEP waves V and VII, respectively, were the two most prominent and reproducible BI components. Wave DVII existed consistently at high, moderate and, in most cases, low stimulus intensities, suggesting that this component is neurogenic although acoustic cross-talk may account for a part of its waveform at high stimulus intensities. The latencies of all BI components increased as a function of decreasing stimulus intensity, while the interpeak intervals, especially DV-DVII, were essentially constant at different intensity levels. The amplitudes of BI components decreased slightly with decreasing intensity. As click repetition rate increased, BI wave latencies and interpeak intervals increased slightly and amplitudes decreased slightly. When repetition rate increased to above 20/s, BI components became poorly differentiated. Lower repetition rates, e.g. 10/s, are therefore preferred for routine derivation of the BI. The changes in the latency and amplitude of BI components with stimulus intensity and repetition rate were associated or concomitant with those of the corresponding BAEP components in monaural and binaural potentials. In view of the concomitant relationship between BI and BAEP latency, we designate BI components in association with the corresponding BAEP components.

Binaural interaction in human neonatal auditory brainstem

Binaural interaction (BI) in brainstem auditory evoked response (BAER) were examined in normal term neonates. The BI components coincided consistently with the latency range of BAER wave IV through wave VII. Most BI components seen in the adults could be identified in the neonates, but the later components, i.e. those with longer latency, were underdeveloped in wave form. Wave DV was the most consistent and reproducible BI component. A marked difference between the neonatal and adult BI wave forms was that wave DVII was particularly small in the neonates. It appears that neuronal responses contributing to later BI components such as wave DVII are particularly immature at birth. Wave latencies and interpeak intervals were longer and amplitudes were smaller in the neonates than in the adults, which was associated with the differences between the neonates and adults in the BAER components. Changes in the BI components with stimulus intensity and rate in the neonates were fundamentally similar to but more significant compared with those in the adults. These findings suggest that neural connections in human auditory brainstem subserving the BI are established at birth but, particularly at higher levels of the brainstem, are immature.

Brainstem auditory evoked responses from birth to adulthood: normative data of latency and interval

Development of wave latency and interpeak interval (IPI) in brainstem auditory evoked responses (BAER) from birth to adulthood was examined. Adult equivalence was reached for most wave latencies and IPIs between the ages of 9 months and 3 years. The observation of the III-V/I-III interval ratio suggests that after term data the I-III IPI decreases more than the III-V IPI. I-III, III-V and I-V IPIs shortened from the l-month old group to the 4-6 year old group by 22%, 15% and 19% respectively. The III-V/I-III interval ration may be a useful BAER measure. Normative data of various BAER measures at different ages are presented. The slope of the L-I function for wave V was slightly steeper in younger groups than in older groups (40 microseconds/dB in the 1-month old group 32 microseconds/dB in the adult group). This change which was accompanied by an age-related difference in the absolute wave latency. It is suggested that age-dependent norms should be used in evaluation of the L-I function.