Cortical, subcortical, and brainstem dysfunction: a correlation in dyslexic children

Transtorno do processamento auditivo (central) em indivíduos com e sem dislexia

TEMA: comparação do transtorno do processamento auditivo (central) em indivíduos com e sem dislexia. OBJETIVO: comparar o transtorno do processamento auditivo (central) em crianças brasileiras com e sem dislexia, por meio dos testes fala com ruído, dicótico de dígitos e padrão de freqüência. MÉTODO: foram avaliadas 40 crianças de 7:0 a 12:11 anos, sendo 20 pertencentes ao grupo com dislexia e 20 pertencentes ao grupo TPA(C). Os testes aplicados envolveram habilidades de fechamento auditivo, figura-fundo para sons lingüísticos e ordenação temporal. RESULTADOS: os indivíduos do grupo TPA (C) apresentaram maior probabilidade de alteração nos testes de fala com ruído e dicótico de dígitos do que os pertencentes ao grupo dislexia. CONCLUSÃO: os sujeitos do grupo dislexia apresentam padrões diferentes de transtorno de processamento auditivo (central), com alteração maior em testes que avaliam o processamento temporal do que em testes que avaliam outras habilidades auditivas.

[Dichotic listening and spect in dyslexic children]

Dichotic listening (DL) was evaluated in 36 children with: verbal dichotic listening test, alternating disyllable dichotic test and non-verbal dichotic listening test. Children were separated into two groups: experimental group with 18 dyslexic children and control group with 18 normal children. Both groups were comparable in gender, laterality and social-economic level. All dyslexic children underwent neuroimaging exam (SPECT). Our data showed that there was a statistical difference between both groups in all DL tests. Abnormal SPECT findings were seen in 50% of the dyslexic children, hypoperfusion of the left temporal lobe being the most frequent abnormality. We conclude that dyslexic children present an impairment of central neurologic processing that may be detected by DL tests, and by functional imaging exam, such as SPECT, as well.

Speech comprehension is correlated with temporal response patterns recorded from auditory cortex

Speech comprehension depends on the integrity of both the spectral content and temporal envelope of the speech signal. Although neural processing underlying spectral analysis has been intensively studied, less is known about the processing of temporal information. Most of speech information conveyed by the temporal envelope is confined to frequencies below 16 Hz, frequencies that roughly match spontaneous and evoked modulation rates of primary auditory cortex neurons. To test the importance of cortical modulation rates for speech processing, we manipulated the frequency of the temporal envelope of speech sentences and tested the effect on both speech comprehension and cortical activity. Magnetoencephalographic signals from the auditory cortices of human subjects were recorded while they were performing a speech comprehension task. The test sentences used in this task were compressed in time. Speech comprehension was degraded when sentence stimuli were presented in more rapid (more compressed) forms. We found that the average comprehension level, at each compression, correlated with (i) the similarity between the frequencies of the temporal envelopes of the stimulus and the subject's cortical activity ("stimulus-cortex frequency-matching") and (ii) the phase-locking (PL) between the two temporal envelopes ("stimulus-cortex PL"). Of these two correlates, PL was significantly more indicative for single-trial success. Our results suggest that the match between the speech rate and the a priori modulation capacities of the auditory cortex is a prerequisite for comprehension. However, this is not sufficient: stimulus-cortex PL should be achieved during actual sentence presentation.

Effectiveness of Central Auditory Processing Tests With Children

The purpose of this investigation was to determine central auditory processing (CAP) individual test efficacy and test battery efficacy and to estimate the costs that are associated with the identification of a targeted sample. Ninety-one children with normal learning (NL) abilities and 147 children with a classroom learning disability (CLD) and presumed CAP disorders (CAPDs) ranging in age from 7 to 13 years were given a battery of seven CAP tests. The test battery consisted of: (1) Binaural Fusion Test (BFT), (2) Masking Level Difference (MLD) test, (3) Filtered Speech Test (FST), (4) Time Compressed Speech (TCS) test, (5) Dichotic Digits Test (DDT), (6) Staggered Spondaic Word (SSW) test, and (7) Pitch Pattern Test (PPT).We believe that this investigation is the first report regarding the assessment of the utility of CAP tests using clinical decision analysis (CDA). We determined that the BFT separated the two samples most effectively and that the FST was the next most effective. A test protocol with BFT and FST or BFT and MLD represented the best battery approach when hit rate, false positive rate, and cost factors were considered. However, if the intent is to be certain that a child with CLD has CAPD given a positive test result, then the BFT and MLD would be the test battery of choice.

Central auditory processing disorder in school-aged children: a critical review

The rationale to evaluate for central auditory processing disorder (CAPD) in school-aged children is based on the assumption that an auditory-specific perceptual deficit underlies many learning problems including specific reading and language disabilities. A fundamental issue in this area is whether convincing empirical evidence exists to validate this proposition. Herein, we consider the issue of modality specificity by examining the extent to which reading, language, and attention disorders in school-aged children involve perceptual dysfunctions limited to a single sensory modality. Difficulty in validating CAPD as a diagnostic label is due in large part to use of the unimodal inclusive framework, which has biased the diagnosis to favor sensitivity of test results over documenting the specificity of the deficit. Indeed, empirical research documenting modality-specific auditory-perceptual dysfunction in this population is scarce. Therefore, the existing literature on this topic has not clarified the "true" nature of the problem, and has left many questions about this disorder unanswered. It is argued that demonstrating modality specificity is one way to rule out supramodal disorders as explanations for observed dysfunction. Multimodal perceptual testing is one logical approach to help clarify this area of investigation.

Learning disabilities and central auditory dysfunction

Hearing loss, whether peripheral or central, compounds the communication and educational problems of the learning disabled student. A central auditory processing disorder uniquely interferes with both the input and integration of verbal information, further resulting in a potentially permanent cognitive dysfunction during the developmental period of acquisition of language. Illustrative cases are presented that indicate the panorama of cognitive dysfunction associated with the learning disabled status. Methods of evaluation and identification and diagnostic criteria are correlated with auditory, visual, and academic performance. Comments regarding clinical awareness, prompt recognition, and ensuing individualized remediation are submitted.

Middle latency response in children with learning disabilities: preliminary findings

The objective of this investigation was to determine if auditory middle latency responses (MLR) obtained from children with learning disabilities (LD) differ from those obtained from children without LD. Simultaneous recordings of auditory brainstem and middle latency responses were obtained in both vertex-ipsilateral (V-I) and vertex-contralateral derivations (V-C) in 22 children (11 LD and 11 normal) in the age range of eight to twelve years whose peripheral hearing was within normal limits to bilateral. The results indicate that for specific recording conditions, the latencies of middle latency responses differ significantly between children with LD and a normal group of children.

Brainstem evoked potentials in learning disabled children

Averaged brainstem auditory responses (BAER) were recorded using left and right ear stimulation with clicks of 90 dBs in two groups of primary school children (control and learning disabled). A linear multiple regression model was used in an attempt to demonstrate the effects of sex, high risk factors related to brain damage and learning disability on the evoked responses. Sex showed a strong influence in the latencies of the first five peaks, with girls having shorter latencies. Risk factors had an effect on the latency of peak V, the I-V interval and the V/I amplitude ration, but only when the left ear was stimulated. Learning disability had no significant influence according to this analysis. Multivariate test of complete homogeneity showed highly significant differences between LD and control boys when the left ear was stimulated and between control and LD girls when the right ear was stimulated. Principal component analyses revealed differences between the two groups: the BAER components of the control subjects showed a minor source of variance when the right ear was stimulated. A contrary effect was observed in LD children. Such differences might be related to ear preference and hemispheric dominance.