Left hemisphere enhancement of auditory activation in language impaired children

Specific language impairment (SLI) is a developmental disorder linked to deficient auditory processing. In this magnetoencephalography (MEG) study we investigated a specific prolonged auditory response (N250m) that has been reported predominantly in children and is associated with level of language skills. We recorded auditory responses evoked by sine-wave tones presented alternately to the right and left ear of 9–10-year-old children with SLI (n = 10) and children with typical language development (n = 10). Source analysis was used to isolate the N250m response in the left and right hemisphere. In children with language impairment left-hemisphere N250m responses were enhanced compared to those of controls, while no group difference was found in the right hemisphere. Consequently, language impaired children lacked the typical right-ward asymmetry that was found in control children. Furthermore, left but not right hemisphere N250m responses correlated positively with performance on a phonological processing task in the SLI group exclusively, possibly signifying a compensatory mechanism for delayed maturation of language processing. These results suggest that enhanced left-hemisphere auditory activation reflects a core neurophysiological manifestation of developmental language disorders, and emphasize the relevance of this developmentally specific activation pattern for competent language development. © 2019, The Author(s).Peer reviewe

Attentional modulation of interhemispheric (a)symmetry in children with developmental language disorder

Publisher Copyright: © 2022, The Author(s).The nature of auditory processing problems in children with developmental language disorder (DLD) is still poorly understood. Much research has been devoted to determining the extent to which DLD is associated with general auditory versus language-specific dysfunction. However, less emphasis has been given to the role of different task conditions in these dysfunctions. We explored whether children with DLD demonstrate atypical interhemispheric asymmetry during the auditory processing of speech and non-speech sounds and whether this interhemispheric balance is modulated by attention. Magnetoencephalography was used to record auditory evoked fields in 18 children (9 to 10 years old), 9 with DLD and 9 with language typical development, during active or passive listening to speech and non-speech sounds. A linear mixed model analysis revealed a bilateral effect of attention in both groups. Participants with DLD demonstrated atypical interhemispheric asymmetry, specifically in the later (185–600 ms) time window but only during the passive listening condition. During the active task, the DLD group did not differ from the typically developed children in terms of hemispheric balance of activation. Our results support the idea of an altered interhemispheric balance in passive auditory response properties in DLD. We further suggest that an active task condition, or top–down attention, can help to regain leftward lateralization, particularly in a later stage of activation. Our study highlights the highly dynamic and interhemispheric nature of auditory processing, which may contribute to the variability in reports of auditory language processing deficits in DLD.Peer reviewe

Speech-brain synchronization: a possible cause for developmental dyslexia

152 p.Dyslexia is a neurological learning disability characterized by the difficulty in an individual¿s ability to read despite adequate intelligence and normal opportunities. The majority of dyslexic readers present phonological difficulties. The phonological difficulty most often associated with dyslexia is a deficit in phonological awareness, that is, the ability to hear and manipulate the sound structure of language. Some appealing theories of dyslexia attribute a causal role to auditory atypical oscillatory neural activity, suggesting it generates some of the phonological problems in dyslexia. These theories propose that auditory cortical oscillations of dyslexic individuals entrain less accurately to the spectral properties of auditory stimuli at distinct frequency bands (delta, theta and gamma) that are important for speech processing. Nevertheless, there are diverging hypotheses concerning the specific bands that would be disrupted in dyslexia, and which are the consequences of such difficulties on speech processing. The goal of the present PhD thesis was to portray the neural oscillatory basis underlying phonological difficulties in developmental dyslexia. We evaluated whether phonological deficits in developmental dyslexia are associated with impaired auditory entrainment to a specific frequency band. In that aim, we measured auditory neural synchronization to linguistic and non-linguistic auditory signals at different frequencies corresponding to key phonological units of speech (prosodic, syllabic and phonemic information). We found that dyslexic readers presented atypical neural entrainment to delta, theta and gamma frequency bands. Importantly, we showed that atypical entrainment to theta and gamma modulations in dyslexia could compromise perceptual computations during speech processing, while reduced delta entrainment in dyslexia could affect perceptual and attentional operations during speech processing. In addition, we characterized the links between the anatomy of the auditory cortex and its oscillatory responses, taking into account previous studies which have observed structural alterations in dyslexia. We observed that the cortical pruning in auditory regions was linked to a stronger sensitivity to gamma oscillation in skilled readers, but to stronger theta band sensitivity in dyslexic readers. Thus, we concluded that the left auditory regions might be specialized for processing phonological information at different time scales (phoneme vs. syllable) in skilled and dyslexic readers. Lastly, by assessing both children and adults on similar tasks, we provided the first evaluation of developmental modulations of typical and atypical auditory sampling (and their structural underpinnings). We found that atypical neural entrainment to delta, theta and gamma are present in dyslexia throughout the lifespan and is not modulated by reading experience

“IT’S ALL RIGHT”. Multimodal rightward spatial bias modified by age and praxis

The general goal of the present work was to study whether spatial perceptual asymmetry initially observed in linguistic dichotic listening studies is related to the linguistic nature of the stimuli and/or is modality-specific, as well as to investigate whether the spatial perceptual/attentional asymmetry changes as a function of age and sensory deficit via praxis. Several dichotic listening studies with linguistic stimuli have shown that the inherent perceptual right ear advantage (REA), which presumably results from the left lateralized linguistic functions (bottom-up processes), can be modified with executive functions (top-down control). Executive functions mature slowly during childhood, are well developed in adulthood, and decline as a function of ageing. In Study I, the purpose was to investigate with a cross-sectional experiment from a lifespan perspective the age-related changes in top-down control of REA for linguistic stimuli in dichotic listening with a forced-attention paradigm (DL). In Study II, the aim was to determine whether the REA is linguistic-stimulus-specific or not, and whether the lifespan changes in perceptual asymmetry observed in dichotic listening would exist also in auditory spatial attention tasks that put load on attentional control. In Study III, using visual spatial attention tasks, mimicking the auditory tasks applied in Study II, it was investigated whether or not the stimulus-non-specific rightward spatial bias found in auditory modality is a multimodal phenomenon. Finally, as it has been suggested that the absence of visual input in blind participants leads to improved auditory spatial perceptual and cognitive skills, the aim in Study IV was to determine, whether blindness modifies the ear advantage in DL. Altogether 180-190 right-handed participants between 5 and 79 years of age were studied in Studies I to III, and in Study IV the performance of 14 blind individuals was compared with that of 129 normally sighted individuals. The results showed that only rightward spatial bias was observed in tasks with intensive attentional load, independent of the type of stimuli (linguistic vs. non-linguistic) or the modality (auditory vs. visual). This multimodal rightward spatial bias probably results from a complex interaction of asymmetrical perceptual, attentional, and/or motor mechanisms. Most importantly, the strength of the rightward spatial bias changed as a function of age and augmented praxis due to sensory deficit. The efficiency of the performance in spatial attention tasks and the ability to overcome the rightward spatial bias increased during childhood, was at its best in young adulthood, and decreased as a function of ageing. Between the ages of 5 and 11 years probably at first develops movement and impulse control, followed by the gradual development of abilities to inhibit distractions and disengage attention. The errors especially in bilateral stimulus conditions suggest that a mild phenomenon resembling extinction can be observed throughout the lifespan, but especially the ability to distribute attention to multiple targets simultaneously decreases in the course of ageing. Blindness enhances the processing of auditory bilateral linguistic stimuli, the ability to overcome a stimulus-driven laterality effect related to speech sound perception, and the ability to direct attention to an appropriate spatial location. It was concluded that the ability to voluntarily suppress and inhibit the multimodal rightward spatial bias changes as a function of age and praxis due to sensory deficit and probably reflects the developmental level of executive functions.Siirretty Doriast

Behavioural manipulations of parietal lobe function

The aim of this thesis was to develop a novel behavioural technique to disrupt parietal function in order to induce top-down cortical modulation of low-level brain structures, namely the brainstem mediated vestibulo- ocular reflex and the early visual cortex. The premise of the technique was based upon using stimuli that engaged overlapping neuronal networks. To this end, we employed a technique that involved concurrent vestibular activation and viewing of bistable perceptual visual stimuli or performing visualised spatial attention tasks. The thesis presents data that shows the ability of this technique to induce a handedness related cortical modulation of the vestibulo-ocular reflex and modulation of the early visual cortex. Subsequently we applied trans-cranial direct stimulation to directly disrupt parietal inter-hemispheric balance in order to induce an asymmetrical modulation of the VOR and propose a revised computational model for vestibular processing. The results from these experiments present the first behavioural demonstration that vestibular cortical processing is strongly lateralised to the non-dominant hemisphere. We propose that this technique developed and validated in this thesis can be used to further probe and investigate cognitive parietal function such as numerical cognition and human decision making.Open Acces

The Biolinguistics of Autism: Emergent Perspectives

This contribution attempts to import the study of autism into the biolinguistics program by reviewing the current state of knowledge on its neurobiology, physiology and verbal phenotypes from a comparative vantage point. A closer look at alternative approaches to the primacy of social cognition impairments in autism spectrum disorders suggests fundamental differences in every aspect of language comprehension and production, suggesting productive directions of research in auditory and visual speech processing as well as executive control. Strong emphasis is put on the great heterogeneity of autism phenotypes, raising important caveats towards an all-or-nothing classification of autism. The study of autism brings interesting clues about the nature and evolution of language, in particular its ontological connections with musical and visual perception as well as executive functions and generativity. Success in this endeavor hinges upon expanding beyond the received wisdom of autism as a purely social disorder and favoring a “cognitive style” approach increasingly called for both inside and outside the autistic community

Encoding of event timing in the phase of neural oscillations

ime perception is a critical component of conscious experience. To be in synchrony with the environment, the brain must deal not only with differences in the speed of light and sound but also with its computational and neural transmission delays. Here, we asked whether the brain could actively compensate for temporal delays by changing its processing time. Specifically, can changes in neural timing or in the phase of neural oscillation index perceived timing? For this, a lag-adaptation paradigm was used to manipulate participants' perceived audiovisual (AV) simultaneity of events while they were recorded with magnetoencephalography (MEG). Desynchronized AV stimuli were presented rhythmically to elicit a robust 1 Hz frequency-tagging of auditory and visual cortical responses. As participants' perception of AV simultaneity shifted, systematic changes in the phase of entrained neural oscillations were observed. This suggests that neural entrainment is not a passive response and that the entrained neural oscillation shifts in time. Crucially, our results indicate that shifts in neural timing in auditory cortices linearly map participants' perceived AV simultaneity. To our knowledge, these results provide the first mechanistic evidence for active neural compensation in the encoding of sensory event timing in support of the emergence of time awareness

Relating alpha power modulations to competing visuospatial attention theories

Visuospatial attention theories often propose hemispheric asymmetries underlying the control of attention. In general support of these theories, previous EEG/MEG studies have shown that spatial attention is associated with hemispheric modulation of posterior alpha power (gating by inhibition). However, since measures of alpha power are typically expressed as lateralization scores, or collapsed across left and right attention shifts, the individual hemispheric contribution to the attentional control mechanism remains unclear. This is, however, the most crucial and decisive aspect in which the currently competing attention theories continue to disagree. To resolve this long-standing conflict, we derived predictions regarding alpha power modulations from Heilman's hemispatial theory and Kinsbourne's interhemispheric competition theory and tested them empirically in an EEG experiment. We used an attention paradigm capable of isolating alpha power modulation in two attentional states, namely attentional bias in a neutral cue condition and spatial orienting following directional cues. Differential alpha modulations were found for both hemispheres across conditions. When anticipating peripheral visual targets without preceding directional cues (neutral condition), posterior alpha power in the left hemisphere was generally lower and more strongly modulated than in the right hemisphere, in line with the interhemispheric competition theory. Intriguingly, however, while alpha power in the right hemisphere was modulated by both, cue-directed leftward and rightward attention shifts, the left hemisphere only showed modulations by rightward shifts of spatial attention, in line with the hemispatial theory. This suggests that the two theories may not be mutually exclusive, but rather apply to different attentional states

Cognitive and anatomical correlates of neglect for peripersonal and extrapersonal space

Spatial neglect is a neurological disorder where patients typically fail to orient or respond to events on their left side. Moreover, recent studies suggest that the severity of neglect may depend specifically on whether stimuli are presented within or beyond arm's reach. However, the evidence for such a general functional dissociation between near and far space processing in the brain remains conflicting: The majority of research has been focussed on line bisection errors which reflect only one small aspect of neglect behaviour. In addition, some behavioural findings suggest a functional dissociation only if a motor response is required. Finally, to date, the critical areas involved in distance related space processing have not been identified.Thus, it remains not only unclear whether neglect in near and far space is a task- and response independent phenomenon but also which damaged brain areas impair distance related space processing. In order to answer these questions the present study compared line bisection and visual search performance and its anatomical correlates in near and far space by using a combined single case- and group study approach.The results showed that neglect restricted to near or far space can vary not only depending on the type of task but also on the type of response required. Visual search tasks were particularly sensitive in detecting the dissociation between those two space sectors. Anatomically, neglect for near space was mainly associated with occipito-parietal lesions and medio-temporal structures, including the posterior cingulate. Neglect for far space was found to result from focal damage of medial, ventro-temporal structures and the prefrontal cortex. In conclusion, neglect for near and far space does not seem to result from a general impairment in distance related processing but from a combination of factors related to specific task demands as well as the location and extent of the brain damage