Function and plasticity of higher-order auditory areas in congenital deafness. Abstract TBC.
Velia Cardin, University College London
Is there a cognitive role for the auditory cortex of deaf individuals? The extraordinary capacity of the brain for functional and structural reorganisation is known as neural plasticity. Understanding this phenomenon not only provides insights into the capabilities of the brain, but also into its potential for adaptation and enhancement, with applications for sensorimotor substitution, artificial intelligence, policy and education.
In cases of congenital sensory deprivation, it is assumed that cortices of the affected sense process information from other senses. Here, I will present evidence from the study of congenital deafness in humans, showing that plasticity mechanisms result in the auditory cortex not only responding to vision and somatosensation, but also being recruited for higher-order cognitive functions such as working memory. I will discuss the anatomical and functional framework that support these plastic changes, its consequences on behaviour and its implications for our understanding of neural plasticity.
Douglas Hartley, NIHR Nottingham Hearing Biomedical Research Unit
Effects of deafness on cortical plasticity: a predictor of cochlear implant outcome? A cochlear implant (CI) is a cost-effective intervention that can restore access to sound following severe-to-profound deafness. Whilst most individuals benefit from their device, speech outcomes vary widely between CI users. Early-onset of hearing loss and/or a long duration of deafness prior to CI surgery are both associated with poor auditory speech perceptual abilities, although a large proportion of variance in CI outcome remains unexplained by these clinical variables alone. Children with congenital hearing loss are often implanted in the first couple of years of life. Current measures of speech perception require behavioural assessments that are only possible in older children. Since very young children are difficult to assess with behavioural techniques, there is an intractable delay of many years between implantation and the detection of poor speech perception. Clinicians subsequently lack the tools to identify these poor performers at an early age and, therefore, are unable to redirect valuable rehabilitation resources to them.
Recent evidence suggests that deafness is associated with cortical plasticity in temporal brain regions that is correlated with CI outcome. Unfortunately, research efforts in this field have been hindered by the incompatibility of most conventional neuroimaging techniques with a CI, due to electro-magnetic artefacts associated with the implanted device. Unlike most other imaging methods, functional near-infrared spectroscopy (fNIRS) is an optically-based technique that is unaffected by these artefacts.
Our research group at the NIHR Nottingham Hearing Biomedical Research Unit has been studying the effects of hearing loss on cortical plasticity using fNIRS, with a long-term goal of developing a clinically-useful prognostic tool for CI outcome. To date we have recorded artefact-free cortical responses to speech in adults after cochlear implantation. We have also shown that fNIRS responses to speech are reproducible between test sessions in normally-hearing adults, at least at a group level. We used fNIRS to confirm findings from previous fMRI experiments, to show that i) temporal brain regions are associated with increased responsiveness to visual stimulation following deafness, and ii) attentive listening to degraded (noise-vocoded) speech leads to increased activation in the left inferior frontal gyrus, compared to a clear-speech in normally-hearing individuals. Subsequently fNIRS may hold promise as a tool to examine cortical ‘cross-modal’ plasticity and neural processes underlying ‘effortful listening’. In a longitudinal study we found that greater cortical activation to lip reading before cochlear implantation was significantly predictive of poorer auditory speech perception in adults after six months of CI use (r=-.75, p<.01). Together these results suggest that fNIRS might support more accurate prognoses of CI outcome in the future. In addition to our adult system, we have recently acquired a paediatric fNIRS system to investigate cortical plasticity in deaf children with and without a cochlear implant.
Mairead MacSweeney,University College London
The influence of language experience on neural plasticity in deaf individuals. Abstract TBC.
Language processing in the visual cortex of the blind. Abstract TBC.
Marcela Peña, Laboratorio de Neurociencias Cognitivas, Pontificia Universidad Católica de Chile.
The role of maturation and experience in neuroplasticity of early cognitive development. The human brain’ structure and function are plastic from gestation. What is the contribution of biology and experience in the development of each human cognitive capacity, is however a question highly unknown.
Recent studies in young infants have shown that some linguistic abilities such as the discovery of the repertory of native phoneme acquisition and the distinction of the native language from others with similar rhythm seem to be more influenced by biology. Other aspects of visual cognition, such as stereo-acuity, and social cognition, such as gaze following, face emotion perception and face-to-face vocalization seem to be more shaped by the amount of experience with the external stimulation. Those and other data renewed questions related to the mechanisms and interventions underpinning an optimal human cognitive development, not only for healthy infants but also for infants who grow up under cognitive risk. We will present some data exploring language acquisition, social communication and rule inferences obtained in healthy full-term and preterm infants, as well as in 4-6 years old children who have been born deaf. We will also show our preliminary data involving foetal cognition. We expect that our data will contribute to the discussion on the origins of how the human brain does adapt to stimulation and learn.
Mary Rudner,Universitet Linköping
Does working memory training improve speech recognition in noise? Abstract TBC.
Rachel Mayberry,University of California San Diego
How Childhood Language Deprivation Illuminates Neuroplasticity in the Language System A challenging question for neurolinguistics is the extent to which the brain’s language system requires linguistic experience during early life to fully develop. Because human languages are independent from the sensory and motor modalities through which they are sent and received, sign language acquisition and processing can be used to investigate this question, which is unavailable to scrutiny with spoken languages. Among the population of deaf signers are unique individuals who, although otherwise healthy, experience little or no language until adolescence or adulthood because they could neither hear the language spoken around them nor see any sign language because it is absent from their environment. We use this naturally occurring variation in the timing of first language acquisition to investigate the development of language structure and neural processing in relation to the brain’s maturational state. This talk focuses on the language
and neural processing of several such individuals, all of whom began to acquire language for the first time between adolescence and adulthood. I will compare and contrast their language function and brain language processing to that of non-language deprived individuals.
Summary/Discussion Day 1 –Jerker Rönnberg, Universitet Linköping
DAY 2, 4th June
Session 3 – Cross-modal plasticity
Amir Amedi, Hebrew University of Jerusalem
Cross-modal plasticity and multisensory integration in the human brain. Abstract TBC.
Stephen Lomber,University of Western Ontario
A causal link between cross-modal reorganization and behaviour In the absence of acoustic input, it is proposed that crossmodal reorganization in deaf auditory cortex may provide the neural substrate mediating compensatory visual functions. In support of this hypothesis we will show that deaf cats are significantly faster at learning to discriminate both human and conspecific faces compared to hearing cats. Moreover, bilateral deactivation of temporal auditory field (TAF) resulted in the elimination of the enhanced face (both conspecific and human) discrimination learning capabilities of deaf cats. Unilateral deactivation of left TAF resulted in a partial, but significant, decrease in the enhanced face learning abilities of deaf cats. These results show that enhanced visual cognition in deaf cats is caused by crossmodal reorganization within TAF of “deaf” auditory cortex. Overall, these results demonstrate a causal link between crossmodal reorganization of auditory cortex and enhanced visual abilities of the deaf, and identified the cortical regions responsible for adaptive visual cognition.
Heidi Baseler,University of York
Visual plasticity in deafness and blindness. Abstract TBC.
Pascal Barone, CNRS CERCO UMR 5549. Pavillon Baudot. CHU Purpan. 31052 Toulouse Cedex, France
Compensatory plasticity in cochlear implanted deaf patients Since Molyneux’s question was first posed in the 17th century, there has been a long debate regarding the capacity of the animal or human brain to process sensory information after a long period of sensory privation. Only limited insights into Molyneux’s problem have been obtained following curable congenital cataracts. However, because profound deafness can now be routinely corrected through a cochlear implant, implanted deaf patients constitute a unique model to study how sensory modalities compete and interact during recovery from a prolonged period of hearing deprivation.
The cochlear implant is a neuroprosthesis that allows profoundly postlingual deaf patients to recover speech intelligibility through long-term adaptive processes to build coherent percepts from the coarse information delivered by the implant. There has been lengthy debate regarding the deleterious or beneficial role of visual speech processing on the capacity of deaf patients to recover auditory speech comprehension after cochlear implantation. In pre-lingual deaf patients, it has been clearly established that the colonization of the auditory areas by visual functions proscribe a restoration of auditory speech processing. For post-lingual CI deaf patients, however, our results reveal a crucial positive influence of the visual cortex on the efficiency of auditory speech comprehension. We suggest the existence of synergetic neural facilitation mechanisms so that a better functional level of one modality leads to the better performance of the other. Furthermore, our present work reinforces the crucial role of the audiovisual integration strategies that are strongly enhanced in CI users to compensate for the poor information delivered by the implant. Such cooperation is a reflection of the multisensory nature of speech communication.
Session 4 – Plasticity across the lifespan
David Corina, University of California Davis
Cross-Modal Plasticity in Deaf Children with Cochlear Implants: language experience effects Cochlear implants (CIs) have become a popular treatment option for deaf children. Deaf children who receive a CI early in life and engage in intensive oral/aural therapy often make great strides in spoken language acquisition. However, despite clinicians’ best efforts, there is a great deal of variability in language outcomes. The multiple factors contributing to this lack of success are poorly understood. One mounting concern is that under conditions of deafness, the auditory system may be subject to cross-modal plasticity (CMP) in which auditory cortex shows specialization for visual processing. We used ERP techniques to assess the presence of cross-modal plasticity in deaf children with cochlear implants. An auditory odd-ball paradigm (85% /ba/ syllables vs. 15% FM tone sweeps) was used to elicit a P1-N1 complex to assess auditory function. Visual evoked potentials were elicited in these same subjects using an intermittent peripheral radial checkerboard while children watched a silent cartoon. This condition was designed to elicit a P1-N1-P2 visual evoked potential (VEP) response. Deaf children with abnormal auditory responses were more likely to have a VEP off-set response that was larger than the VEP onset response (a pattern opposite of what is normally observed in VEP studies). VEP data show an unusual topographic distribution with extension to midline site Cz. These data may indicate evidence of cross-modal plasticity in deaf children with cochlear implants. We discuss the contributions of signed and spoken language experience in the expression of these results.
Torsten Baldeweg, University College London
Growing up with brain lesions: structural constraints and functional plasticity. Abstract TBC.
Anu Sharma, University of Colorado Boulder
Cortical re-organization in hearing loss across the life span A basic tenet of neuroplasticity is that the brain will re-organize following sensory deprivation. Compensation for the deleterious effects of hearing loss may include recruitment of alternative or additional brain networks to perform auditory tasks. Our high-density EEG experiments suggest that deaf children, as well as adults with early-stage, age-related hearing loss show significant changes in neural resource allocation including cross-modal recruitment by visual and/or somatosensory modalities. Cortical re-organization appears to influence the variability in speech perception outcomes seen in children and adults with hearing loss. Overall, our results suggest that compensatory cortical plasticity secondary to auditory deprivation has important consequences across the life span in patients with hearing loss.
Supported by the US National Institutes of Health.