Maturation of human central auditory system activity: separating auditory evoked potentials by dipole source modeling.

OBJECTIVES

Previous studies have shown that observed patterns of auditory evoked potential (AEP) maturation depend on the scalp location of the recording electrodes. Dipole source modeling incorporates the AEP information recorded at all electrode locations. This should provide a more robust description of auditory system maturation based on age-related changes in AEPs. Thus, the purpose of this study was to evaluate central auditory system maturation based dipole modeling of multi-electrode long-latency AEPs recordings.

METHODS

AEPs were recorded at 30 scalp-electrode locations from 118 subjects between 5 and 20 years of age. Regional dipole source analysis, using symmetrically located sources, was used to generate a spatio-temporal source model of age-related changes in AEP latency and magnitude.

RESULTS

The regional dipole source model separated the AEPs into distinct groups depending on the orientation of the component dipoles. The sagittally oriented dipole sources contained two AEP peaks, comparable in latency to Pa and Pb of the middle latency response (MLR). Although some magnitude changes were noted, latencies of Pa and Pb showed no evidence of age-related change. The tangentially oriented sources contained activity comparable to P1, N1b, and P2. There were various age-related changes in the latency and magnitude of the AEPs represented in the tangential sources. The radially oriented sources contained activity comparable to the T-complex, including Ta, and Tb, that showed only small latency changes with age. In addition, a long-latency component labeled TP200 was observed.

CONCLUSIONS

It is possible to distinguish 3 maturation groups: one group reaching maturity at age 6 and comprising the MLR components Pa and Pb, P2, and the T-complex. A second group that was relatively fast to mature (50%/year) was represented by N2. A third group was characterized by a slower pattern of maturation with a rate of 11-17%/year and included the AEP peaks P1, N1b, and TP200. The observed latency differences combined with the differences in maturation rate indicate that P2 is not identical to TP200. The results also demonstrated the independence of the T-complex components, represented in the radial dipoles, from the P1, N1b, and P2 components, contained in the tangentially oriented dipole sources.