Refractory effects on auditory-evoked responses in children with reading disorders

Stability of P50 auditory sensory gating during sleep from infancy to 4 years of age

The stability of cerebral inhibition was assessed across early childhood using a paired-click auditory sensory gating paradigm. The P50 ERP was measured during REM (or its infant analogue, active sleep) and NREM sleep in 14 children at approximately 3 months of age and again at approximately 4 years of age. Evoked response amplitudes, latencies, and the S2/S1 ratio of the amplitudes of the evoked responses were compared between the two visits. Significant reliability was found for the S2/S1 ratio (r = .73, p = .003) during REM but not non REM sleep (r = -.05, p = .88). A significant stimulus number by sleep stage interaction (F(1,12) = 17.1, p = .001) demonstrated that the response to the second stimulus decreased during REM but not NREM sleep. These findings suggest that this measure is stable during REM sleep across early childhood, is not affected by age, and is sleep-state dependent. P50 sensory gating is a biomarker which, if used properly, may provide a mechanism to further explore changes in the developing brain or may help with early screening for psychiatric illness vulnerability.

Atypical auditory refractory periods in children from lower socio-economic status backgrounds: ERP evidence for a role of selective attention

Previous neuroimaging studies indicate that lower socio-economic status (SES) is associated with reduced effects of selective attention on auditory processing. Here, we investigated whether lower SES is also associated with differences in a stimulus-driven aspect of auditory processing: the neural refractory period, or reduced amplitude response at faster rates of stimulus presentation. Thirty-two children aged 3 to 8 years participated, and were divided into two SES groups based on maternal education. Event-related brain potentials were recorded to probe stimuli presented at interstimulus intervals (ISIs) of 200, 500, or 1000 ms. These probes were superimposed on story narratives when attended and ignored, permitting a simultaneous experimental manipulation of selective attention. Results indicated that group differences in refractory periods differed as a function of attention condition. Children from higher SES backgrounds showed full neural recovery by 500 ms for attended stimuli, but required at least 1000 ms for unattended stimuli. In contrast, children from lower SES backgrounds showed similar refractory effects to attended and unattended stimuli, with full neural recovery by 500 ms. Thus, in higher SES children only, one functional consequence of selective attention is attenuation of the response to unattended stimuli, particularly at rapid ISIs, altering basic properties of the auditory refractory period. Together, these data indicate that differences in selective attention impact basic aspects of auditory processing in children from lower SES backgrounds.

Electrophysiological evidence for attenuated auditory recovery cycles in children with specific language impairment

Previous research indicates that at least some children with specific language impairment (SLI) show a reduced neural response when non-linguistic tones were presented at rapid rates. However, this past research has examined older children, and it is unclear whether such deficits emerge earlier in development. It is also unclear whether atypical refractory effects differ for linguistic versus non-linguistic stimuli or can be explained by deficits in selective auditory attention reported among children with SLI. In the present study, auditory refractory periods were compared in a group of 24 young children with SLI (age 3-8 years) and 24 matched control children. Event-related brain potentials (ERPs) were recorded and compared to 100 ms linguistic and non-linguistic probe stimuli presented at inter-stimulus intervals (ISIs) of 200, 500, or 1000 ms. These probes were superimposed on story narratives when attended and ignored, permitting an experimental manipulation of selective attention within the same paradigm. Across participants, clear refractory effects were observed with this paradigm, evidenced as a reduced amplitude response from 100 to 200 ms at shorter ISIs. Children with SLI showed reduced amplitude ERPs relative to the typically-developing group at only the shortest, 200 ms, ISI and this difference was over the left-hemisphere for linguistic probes and over the right-hemisphere for non-linguistic probes. None of these effects was influenced by the direction of selective attention. Taken together, these findings suggest that deficits in the neural representation of rapidly presented auditory stimuli may be one risk factor for atypical language development.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Maturation of obligatory auditory responses and their neural sources: evidence from EEG and MEG

Neural auditory responses are known to change from childhood to adulthood. The most prominent components of the event-related potentials (ERPs) found in children are the P1 and N2, while the P1 and N1 are strongest in adults. Previous dipole localizations showed regions of the auditory cortex (AC) underlying these responses. An N1 in children, however, has only been observed in older age or under certain experimental conditions different than commonly applied in adults. The current study aimed to further elucidate on auditory processing and related components in school-aged children. To do this, MEG and EEG was recorded in adults and 9 to 10year old children, while presenting pure tones either repetitively or randomly among tones of different pitch. Furthermore, the current paradigm was explicitly designed to not only investigate the P1 and N2 in children, but moreover to examine N1 modulations based on different refractory states caused by the two conditions. Our results are clear cut. In adults, P1(m) and N1(m) components were localized in AC regions, with the N1(m) largely attenuated for repetitive tones. The P1(m) and N2(m) components observed in children were also localized in AC regions. Most importantly, ERP modulations in the N1 time window (i.e., larger responses for random than repetitive tones) were remarkably similar for adults and children, both in amplitude and latency. This effect indicates that the N1 sub-component reflecting frequency-specific refractoriness is fully developed in 9 to 10year old children. Thus, previous interpretations on the function and maturation of the N1 need reconsideration.

Auditory word perception in sentence context in reading-disabled children

Reading difficulties seem to be related to a phonological deficit that has its origin in poor speech perception. As such, disabled readers may use contextual cues to compensate for their weak speech perception abilities. We compared good and poor readers, 7-13 years old, on auditory perception of words varying in phonological contrast, in congruent versus incongruent sentence contexts. Both groups did worse in the phonologically similar than in the phonologically dissimilar incongruent condition. Magnetoencephalography revealed differential activation between the groups as a function of phonological contrast in left superior temporal gyrus between 200 and 300 ms, suggesting that poor readers may have processed phonologically similar incongruent stimuli as congruent. The results are consistent with a phonological account of reading disability.

Reliability of P50 auditory sensory gating measures in infants during active sleep

This study assessed reliability of auditory sensory gating in young infants from 1-4 months of age using a paired-click paradigm in which auditory 'clicks' were presented at an interstimulus interval of 500 ms. Evoked potential component P1 was measured during periods of active sleep on two different occasions. Amplitudes, latencies, and ratio of the evoked potentials to each of the auditory clicks were compared. Significant reliability was found in the response ratio, response latency to the first stimulus, and response amplitude to the second stimulus, with a trend toward significance for response latency to the second stimulus and response amplitude to the first stimulus. The results suggest that auditory sensory gating can be reliably measured during active sleep in young infants and might be a useful tool in the study of neurodevelopmental disorders.