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 central auditory processing disorder in impaired language development. The study focused on the differences in latency, amplitude, and topography of the auditory evoked long-latency components, P2 and N2, and the potential diagnostic value of these parameters.


METHODS
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 time of 20 msec. The intensity was 75 dB HL. Six test sequences of 50 stimuli an interval of 1.0 sec were presented to the left and to the right ear separately. The AEPs were recorded and analyzed with the Bio-Logic Brain Atlas III program.


RESULTS
In the topographic maps, a focus of positive potential corresponding to P2 (FP2) and a focus of negative potential corresponding to N2 (FN2) were seen in the majority of children, with a similar distribution in the two groups. The latencies 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 P2 and N2 latency, amplitude, and topography in identifying the LI subjects, was estimated by means of a scoring system. With all three parameters together, the sensitivity was calculated to be 80% and the specificity 80%. Statistical mapping of the latency interval of 135 to 305 msec showed z maps with regions of > or = 3 SD in 14 subjects in the LI group and eight subjects in the C group.


CONCLUSIONS
The deviations in the LI group indicate slower processing in central auditory pathways rather than differences in location and orientation of generators. The deviating topography seen in some LI subjects may reflect the various sites and extent of cerebral dysfunction. The results also support the idea of different generators for the P2 and N2 components. Topographic evaluation of long-latency AEPs may become a diagnostic tool in language disorders. The scoring system is a potential model in the establishment of individual diagnostic variables.
Tonnquist-Uhlén
I
I
Department of Audiology, Karolinska Hospital, Stockholm, Sweden.
D000293:Adolescent; D001303:Auditory Cortex / Q000503:physiopathology; D001931:Brain Mapping; D002648:Child; D005072:Evoked Potentials, Auditory; D005260:Female; D006801:Humans; D007806:Language Disorders / Q000503:physiopathology*; D008297:Male; D012720:Severity of Illness Index; D013064:Speech Disorders / Q000503:physiopathology*; D013067:Speech Perception