Biomedical subjects

I Tonnquist-Uhlén

Publications and source records attributed to I Tonnquist-Uhlén.

5 recordsLinked to original sources

PubMed1996

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. 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 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.

Adolescent↗

PubMed1996

Topography of auditory evoked long-latency potentials in children with severe language impairment: the T complex.

Topographic maps of the late auditory evoked potentials (AEP) were studied in a group of 20 children, aged 9-15 years, with severe language impairment (LI) and an age-matched control (C) group of 20 normal children. The stimulus was a pure tone at 500 Hz with a duration of 100 ms and a rise and fall time of 20 ms. The intensity was 75 dB HL. Six test sequences of 50 stimuli at an interval of 1.0 s were presented to the left and right ear separately. Grand average maps of all the children in the LI and the C group, separately, were calculated and showed a bilateral negativity over the temporal areas, corresponding to the negative peak of the T complex (Tb) at a latency of about 150 ms. The amplitudes were larger contralateral to the stimulated ear in both groups. A difference map between the two grand average maps showed topographic differences at temporal sites. However, the T complex could not be identified in 7 LI children and 1 C child. In the remaining subjects with a T complex the topographic pattern was similar in the two groups but with lower amplitudes and significantly longer latencies in the LI group. The presence and latency of the positive peak of the T complex (Ta) was also examined, showing significant between-group differences. The value of Tb, in diagnosing language impairment, was tested by means of a scoring system and with statistical mapping. The diagnostic sensitivity of Tb latency, amplitude and topography in selecting the LI children was 90% to 40% with a specificity of 80% to 95%. The results indicate slower and deviating processing in the central auditory pathways of LI children. The variation in results between children, with missing components or prolonged latencies in the majority, but not all, of the LI children, may be explained by different pathophysiological causes of their language impairment. The more pronounced deviations of the T complex compared with the vertex-recorded NI may also indicate a specific role of the T complex-related cortical activity in language impairment.

Adolescent↗

PubMed1996

Topography of auditory evoked cortical potentials in children with severe language impairment.

Development of normal speech and language functions is closely related to normal hearing. However, most children with delayed or disturbed speech development show normal tone thresholds and here the investigation has to include higher levels in the auditory system. There is evidence for a connection between language impairment and a central auditory processing disorder, but the underlying mechanisms are not well understood. There is also a need for objective diagnostic methods of central auditory function. In the present study, a computerised method of mapping the scalp topography of long-latency (cortical) auditory evoked potentials (LAEP) was used for assessment of the function in central auditory pathways. Topographic mapping of the LAEP component N1, in adults and normal children, showed reproducible and valid results. In adults, a focal negativity, focus of NI (FNI), with a frontocentral position and contralateral to the stimulated ear was observed. The N1 maps in normal children showed a pattern similar to that in adults, but with some age-related changes. The N1 latencies declined significantly with age in normal children and reached adult values at the ages of 14-16 years. The topography of the LAEP components N1, P2, N2 and the T complex was investigated in 20 children with severe language impairment (LI). The study also included auditory brainstem responses (ABR), electroencephalography (EEG), quantitative EEG (qEEG) and magnetic resonance imaging (MRI). Twenty normal children served as controls (C). A similar topographic pattern was found in the LI and the C children, but with a higher proportion of deviating and non-focal maps in the LI group. The latencies of all components were significantly longer in the LI than in the C children. The diagnostic value of LAEP topography, latency and amplitude was estimated with a scoring system, whereby significantly higher scores were found in the LI group than in the C group. With all three parameters together the sensitivity was 65%, with a specificity of 90%. There was a high degree of pathological EEGs in the LI group. ABR abnormalities were seen in some LI subjects. MRI was normal in all but two LI children. There was no significant correlation between the results of EEG, ABR, MRI and the total score of LAEP, but some LI children showed a wide pathological pattern. In 17 of the 20 LI subjects a pathological result was obtained in one or more of the investigations. In conclusion, our results may indicate that language impairment has a dual pathophysiology, a specific auditory disorder (LAEP, ABR) and a non-specific general cerebral disturbance (EEG, MRI). The highly varying results among the present LI children, with specific and/or non-specific deviations, may be due to heterogeneity of the group with different aetiologies of their language impairment, or to a general developmental disturbance with a varying distribution and penetrance. The scoring system of LAEP proved to be the most sensitive method in separating the LI children from the controls. This may be a promising model for individual diagnostic criteria and for classification of language impairment.

Adolescent↗

PubMed1995

Topography of auditory evoked long-latency potentials in normal children, with particular reference to the N1 component.

Topographic maps of late auditory evoked potentials were obtained with the Brain Atlas III system in 34 healthy, normal hearing children aged 8-16 years. The stimulus was a 100 msec, 500 Hz tone burst, presented separately to the left and right ears, at 75 dB HL. The resulting auditory evoked potentials showed a prominent N1, after about 100 msec, and a topographic map with a corresponding fronto-lateral focus designated as the focus of N1 (FN1). Foci with varying positions and amplitudes were identified in 33 of 34 subjects after left ear stimulation and in 29 of 32 subjects after right ear stimulation. The topography showed a high degree of stability in most subjects, with the position of the negative "peak" of FN1 in front of the interaural line and with a dominance contralateral to the ear stimulated. There was a significant decrease in the latency of N1 with increasing age. FN1 tended to change position with age and some differences from adults were also observed. In conclusion, a distinct topographic pattern of the N1 component of the late auditory evoked potentials was seen in the majority of children. It remains to be established to what extent this method may be clinically useful for disclosing functional disturbances in the central auditory pathways.

Acoustic Stimulation↗

PubMed1989

Auditory stimulation brain map.

The topography of auditory evoked potentials (AEPs) was studied in 12 neurologically normal, adult, right-handed subjects of either sex. The AEPs were recorded with seventeen active electrodes in response to 500 Hz tone bursts with a level of 75 dB HL presented either to the left or the right ear. AEP brain maps were obtained with the BRAIN ATLAS III system. A region of maximum negativity was obtained corresponding to N1 at vertex and defined as focus of N1 (FN1). The reproducibility within and between sessions of FN1 was studied and found to be good for most of the subjects. The interindividual variability was moderate and the centre of FN1 on the map was localized 7 mm in front of the vertex electrode and 8.4 and 8.0 mm to the contralateral side of the vertex electrode upon stimulation of the left and the right ear, respectively. The approximate position of the skull surface is obtained by multiplication by a factor of 3. It was concluded that a standardized test session including six single maps based on 50 stimuli each gives an average map with identifiable and reproducible focus. The basis seems to be fulfilled to use the brain map in further analysis on clinical material.

Adult↗