TOPOGRAPHY OF AUDITORY-EVOKED LONG-LATENCY POTENTIALS IN CHILDREN WITH SEVERE LANGUAGE IMPAIRMENT - THE P2 AND N2 COMPONENTS

Objective: To establish objective neurophysiological correlates of a c entral auditory processing disorder in impaired language development. The study focused on the differences in latency, amplitude, and topogr aphy of the auditory evoked long-latency components, P2 and N2, and th e potential diagnostic value of these parameters. Design: Topographic maps of the late auditory evoked potentials (AEPs) were obtained in a group of 20 children, aged 9 to 15 yr, with severe language impairment (LI) and in a control (C) group of 20 normal children. Stimulus was a pure tone at 500 Hz with a duration of 100 msec and a rise and fall t ime of 20 msec. The intensity was 75 dB BL. Six test sequences of 50 s timuli at an interval of 1.0 sec were presented to the left and to the right ear separately. The AF:Ps were recorded and analyzed with the B io-Logic Brain Atlas III program. Results: In the topographic maps, a focus of positive potential corresponding to P2 (FP2) and a focus of n egative potential corresponding to N2 (FN2) were seen in the majority of children, with a similar distribution in the two groups. The latenc ies of P2 and N2 were significantly longer in the LI group than in the C group, P2 showing the most pronounced difference. The amplitudes of FP2 and FN2 were lower in the LI group. The diagnostic value of the P 2 and N2 latency, amplitude, and topography in identifying the LI subj ects, was estimated by means of a scoring system. With all three param eters together, the sensitivity was calculated to be 80% and the speci ficity 80%. Statistical mapping of the latency interval of 135 to 305 msec showed z maps with regions of greater than or equal to 3 SD in 14 subjects in the LI group and eight subjects in the C group. Conclusio ns: The deviations in the LI group indicate slower processing in centr al auditory pathways rather than differences in location and orientati on of generators. The deviating topography seen in some LT subjects ma y reflect the various sites and extent of cerebral dysfunction. The re sults also support the idea of different generators for the P2 and N2 components. Topographic evaluation of long-latency AEPs may become a d iagnostic tool in language disorders. The scoring system is a potentia l model in the establishment of individual diagnostic variables.