Download Neural Plasticity Workshop: Insights from

Neural Plasticity Workshop: Insights from Deafness and Language
3r & 4th June. Wellcome Collection Conference Centre
DAY 1, 3rd June
Welcome/Introduction – Bencie Woll, University College London
Session 1 – Deafness and neural plasticity
Andrej Kral, Medical University Hanover
Function and plasticity of higher-order auditory areas in congenital deafness.
Congenital deafness leads to numerous functional deficits within the auditory system that cannot be
compensated if hearing restoration starts in adulthood, resulting in critical period for hearing therapy (Kral,
2013, Neurosci). In this process, both developmentally-decreasing synaptic plasticity and deficits in cortical
microcircuitry responsible for integration of top-down interactions into bottom-up stream of processing are
involved. That opens the question how well neurons in higher-order areas can be activated by the input
through the deprived modality late in life, and whether their top-down interconnections to lower order areas
can develop in absence of hearing. Apart from the unused auditory brain resources, some auditory structures
take over non-auditory (cross-modal) functions in congenital deafness. Such cross-modal reorganization may
be either adverse or beneficial for sensory restoration. In congenitally deaf cats, supranormal visual behavior is
mediated by higher-order auditory fields (Lomber et al., 2010, Nat Neurosci). General anatomical connectivity,
despite some weak ectopic projections (Barone et al., 2013, PLoS One), and general auditory responsiveness in
both the primary (Kral et al., 2009, J Neurosci) and these higher-order fields (Land et al., 2016, J Neurosci) are
preserved in absence of auditory experience. The existing data suggest a dichotomy between preservation of
gross anatomical connectivity in congenital deafness and functional deficits in the same circuits. Also the crossmodal reorganization is caused more by functional changes and less by anatomical reorganization. In total, the
data are consistent with the hypothesis of a reduced corticocortical functional coupling between cortical
auditory areas in congenital deafness (Kral and Sharma, 2012, TINS).
Supported by Deutsche Forschungsgemeinschaft (Kr 3370 and Cluster of Excellence Hearing4All)
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-toprofound 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.
The majority of our knowledge about the neurobiology of language processing comes from studies of spoken
languages. The study of signed languages allows a unique perspective and allows us to determine whether
what the field has learnt so far is characteristic of alllanguages or whether it is specific to languages that are
spoken and heard. I will present a review of the literature which suggests that although differences have been
identified in the neural systems supporting sign and speech processing, in particular in the left parietal lobe,
the networks recruited are extremely similar. Both languages recruit a predominantly left-lateralised
perisylvian network. Of particular interest for this workshop is the extent of plasticity of the superior temporal
cortices within this left perisylvian network. I will present data from recent studies in which we have addressed
the influence of age of sign language acquisition, deafness, stimulus material and task requirements on
plasticity within the superior temporal cortices. These studies provide new insights into the functional role of
‘auditory association’ regions in those born profoundly deaf.
Session 2 – Language plasticity
Marina Bedny, Johns Hopkins University
Language processing in the visual cortex of the blind.
How do genes and experience shape neurocognitive development? Insights into this question come from
studies of language in blind individuals. Blind children have less sensory access to the referents of linguistic
utterances, particularly those that describe seeing and light (e.g. sparkle, stare.) I will present evidence that
despite this, congenitally blind adults have typical meanings of visual verbs and typical neural representations
of verbs. More generally, the fronto-temporal system that supports language processing is preserved in blind
individuals. However, the neurobiology of language in blindness is changed in several surprising ways. First,
fronto-temporal language areas are less left-lateralized in blind than sighted individuals. Strikingly, in blindness
“visual” areas of occipital cortex are incorporated into the language network. Areas of occipital cortex,
including V1, respond to the meanings of words and the compositional structure of sentences. These “visual”
areas are not active during closely matched non-linguistic tasks and are functionally coupled with frontotemporal language areas during language processing and at rest. Visual cortices are incorporated into the
language system during brain development. Individuals who become bind as adults do not develop languagerelated plasticity in visual cortex and in blind children plasticity emerges by 4-years-of-age, prior to Braille
acquisition. In our most recent data, we find that ventral occipital areas that support visual letter and word
recognition during reading in sighted individuals (i.e. the visual word form area) come to support lexical and
syntactic processing in blindness. Together these findings suggest that experience during development is a
major determinant of the neurobiology of language. The same language “software” has many possible neural
instantiations.
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?
Listening to speech in noise is often reported to be effortful, especially for individuals with hearing
impairment, and many studies have shown that the ability to recognize speech in noise is positively associated
with working memory capacity. We reasoned that if working memory capacity could be increased by training
this might improve the ability to recognize speech in noise and modulate the neural activation associated with
it. Adults with normal (NH) and impaired hearing (HI) were randomized to five weeks of CogMed QM training
followed by five weeks of no training, or vice versa, according to a crossover design. Auditory and cognitive
abilities were tested on four occasions: pre-training, T1; after 5 weeks, T2; after 10 weeks, T3 and after a
further six months, T4. During fMRI scanning at T1, T2 and T3, the participants listened to stereotyped matrix
type sentences in pink noise and competing talker noise at individually adapted 50% and 90% intelligibility
levels as well as in quiet. Behavioural results show that although HI had worse auditory abilities than NH, there
was no significant difference in cognitive ability, with the exception of phonological processing, which tended
to be slower (cf Classon et al. 2013). Performance on most of cognitive tasks improved across sessions,
although this could not be specifically attributed to training. We found no consistent pattern of correlations
between working memory and the ability to understand speech in noise either before or after training. fMRI
results did not reveal any significant effect of training and furthermore there was no significant effect of
hearing status. However, there was a significant between group difference in activation of the left temporal
gyrus (-44 -23 10) for the contrast speech in pink noise (across intelligibility levels) vs clear speech. There was
also an interaction (p < .001 uncorrected) between group and testing occasion in the right superior frontal
gyrus (7 58 16) for the contrast speech in noise (across types and levels) vs clear speech. Further, activation in
left superior temporal gyrus (-56 -20 -2) correlated more strongly with intelligibility in NH compared HI
participants.
These results suggest that even when cognitive abilities are matched and intelligibility is individually adjusted,
there are differences relating to hearing impairment in the neural mechanisms supporting speech in noise
processing. The pattern of results suggests hearing-related differences in bottom-up processing mechanisms
across time and hearing-related differences in top-down mechanisms that change over time. However, we
found no evidence that working memory training improves speech recognition in noise.
References
Classon, E., Rudner, M. & Rönnberg, J. (2013). Working memory compensates for hearing related
phonological processing deficit. Journal of Communication Disorders, 46, 17-29.
doi:10.1016/j.jcomdis.2012.10.001
CogMed QM, developed by CogMed Cognitive Medical Systems AB, Stockholm, Sweden, 2006
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
Plasticity and stability in the Human Brain: lessons from multisensory longitudinal studies.
I will describe the extent and timescale with which sensory cortices can be recruited and modified by inputs
coming from various natural or artificial sensory input modalities or even when conveying high-level cognitive
information. Our approach uses longitudinal studies in individuals with various degrees of visual deprivation,
ranging from sighted-blindfolded to lifelong deprivation in patients with undeveloped retinas. I will describe
the two main types of plasticity that we observed in the brain: (1) task-switching plasticity; and (2) taskselective sensory-independent organization. I will propose possible mechanisms that might give rise to such
brain (re)-organization. In addition, I will show how we recently expanded our theoretical framework to
include possible developmental mechanisms and implications for clinical rehabilitation including the
development of a multisensory approach to restore vision (e.g. the multisensory bionic eye). By presenting an
overview of our findings I will question classical theories of 'critical periods' by showing that "visual" regions do
maintain their specific typical functionality and functional connectivity patterns even if "reawakened" in later
periods in life including adulthood. Overall, through our approach and findings, new insights will emerge into
the effects of learning and training on the (re)-organization principles of the human brain.
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.
Sound can help people orient their attention/gaze towards peripheral events outside their central line of sight.
Without sound, people must rely on vision to keep track of both central and peripheral events simultaneously.
Consequently, deaf adults that have spent a lifetime honing this skill can perform better on certain peripheral
visual tasks than hearing adults. What biological changes (plasticity) might help bring about this ability? One
solution is to recruit unused brain areas that normally process sound. Another strategy, evident in those with
congenital partial sight loss, is to modify structures that process visual information. To address the latter
possibility, we investigated whether structures along the visual pathway differed between congenitally,
profoundly deaf adults and hearing adults. Using several techniques (MRI, EEG, ERG, OCT), we measured
anatomical characteristics and physiological responses from the eyes and brains of deaf and hearing
participants, specifically comparing the parts involved in central and peripheral vision. In hearing adults, there
is a large bias towards processing information from the centre of the visual field. In deaf adults, on the other
hand, converging lines of evidence suggest that there is a shift in the balance between central and peripheral
processing. Moreover, this shift appears to be present not only in visual parts of the brain but also as early in
the visual pathway as the eye. This suggests that modifications may occur at various stages along the visual
pathway in response to changing demands on vision.
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 offset 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
Plasticity in the developing brain: impact of focal lesions on language networks.
Left hemisphere dominance for language is found in the great majority of humans and injury to left
hemispheric language regions in adults often leads to severe and chronic deficits. Similar injury suffered in
childhood, however, does not commonly result in chronic language deficits. This has been attributed to the
plasticity of the developing brain, enabling it to reorganise language faculties to the right hemisphere. I will
begin with a review of literature on functional maturation of the language system throughout childhood and
adolescence. I will then show patterns of language reorganisation observed using functional imaging in cohorts
of children with injury incurred at different times and in different locations in the brain, including children with
stroke injury and lesional focal epilepsy. I will review the major findings from those studies, identifying factors,
which promote inter-hemispheric language shifts. I will also show case studies of patients who underwent
surgical resection within the language-dominant hemisphere. A greater understanding of the neural
mechanisms which shape the lateralized patterning of cortical networks remains an important question for
future research, as it might offer insights into mechanisms of recovery of function after neurological injury.
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 crossmodal 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.
Summary/Discussion Day 2 – Ruth Campbell