Maturation of human central auditory system activity: the T-complex.

Objective: The purpose of this study was to evaluate and describe the maturation of a set of auditory evoked potentials (AEPs) described as the T-complex from a large group of children, adolescents, and young adults who ranged in age from 5 to 20 years of age.

Methods: The AEPs evoked by brief trains of clicks presented to the left ear were measured at 30 scalp-electrode locations. Analyses focused on age-related latency and amplitude changes in the T-complex recorded at the temporal electrode sites T3 and T5 over the left hemisphere and T4 and T6 over the right hemisphere. The maturation of the T-complex components Na, Ta, and Tb was contrasted with those of the obligatory AEPs P1, N1b, and P2 measured at electrodes C3 and C4.

Results: T-complex activity was present in the grand average AEPs of all 14 age groups spanning ages 5-20 years. T-complex components recorded at electrodes T3 and T4 differed in both morphology and maturation rate from those recorded at T5 and T6. In contrast to the prolonged maturation of AEP latency measured at electrodes T5 and T6, the T-complex components measured at electrodes T3 and T4 did not show a significant overall change in peak latency as a function of age. Consistent amplitude and latency correlations were found between the obligatory AEP components P1, N1b and P2 recorded at C3 and C4 and the T-complex components measured at T5 and T6, but not T3 and T4.

Conclusions: Distinct patterns of AEP maturation were measured at electrode sites commonly used to record the T-complex. At scalp electrodes located over more posterior temporal areas (T5 and T6), the AEPs were characterized by a prolonged pattern of maturation very similar to that measured at the central electrodes C3 and C4. These findings and others reported in this paper provide strong evidence that the AEPs recorded at electrodes T5 and T6 are not T-complex peaks. In contrast, the AEPs measured at electrodes T3 and T4 over more anterior temporal scalp areas appear largely independent of activity measured at the central electrode locations. The T-complex peaks Ta and Tb measured at these scalp locations mature early, with no overall significant age-related changes in peak latencies.

Significance: The T-complex is recorded from the temporal electrodes T3 and T4 represents activity of secondary auditory cortex better than, and independent from, midline potentials. Its robust presence in 5-8 year olds supports its potential usefulness in assessing language impairment.