The adaptive brain: A neurophysiological perspective

Learning-induced neural plasticity of speech processing before birth

Learning, the foundation of adaptive and intelligent behavior, is based on plastic changes in neural assemblies, reflected by the modulation of electric brain responses. In infancy, auditory learning implicates the formation and strengthening of neural long-term memory traces, improving discrimination skills, in particular those forming the prerequisites for speech perception and understanding. Although previous behavioral observations show that newborns react differentially to unfamiliar sounds vs. familiar sound material that they were exposed to as fetuses, the neural basis of fetal learning has not thus far been investigated. Here we demonstrate direct neural correlates of human fetal learning of speech-like auditory stimuli. We presented variants of words to fetuses; unlike infants with no exposure to these stimuli, the exposed fetuses showed enhanced brain activity (mismatch responses) in response to pitch changes for the trained variants after birth. Furthermore, a significant correlation existed between the amount of prenatal exposure and brain activity, with greater activity being associated with a higher amount of prenatal speech exposure. Moreover, the learning effect was generalized to other types of similar speech sounds not included in the training material. Consequently, our results indicate neural commitment specifically tuned to the speech features heard before birth and their memory representations.

The mismatch negativity (MMN) brain response to sound frequency changes in adult cochlear implant recipients: a follow-up study

CONCLUSION

Plasticity of auditory pitch discrimination driven by cochlear implant (CI) use uring a 2.5-year follow-up was indicated by an enhancement of the amplitude of mismatch negativity (MMN) event-related brain potential (ERP) to pure tone frequency changes.

OBJECTIVES

To follow up changes in MMN elicited to frequency and duration changes in tones during 2.5 years of CI use and to compare MMN results with audiometric speech recognition scores (SRSs).

METHODS

Postlingually deafened adults with Cochlear Nucleus CI-22 and spectra processor with SPEAK strategy were recruited. MMN was measured at 1 and 2.5 years after CI activation. Repetitive 100 ms standard tones with a frequency of 500, 1000, 2000 or 4000 Hz in separate sequences were delivered to participants concentrating on a silent movie. Deviant tones occurring infrequently among standard tones were 20% lower in frequency or 50% shorter in duration than the standards. Speech recognition ability was followed with SRSs.

RESULTS

Both time from CI activation and the frequency range of tones had significant effects on the MMN amplitude. A significant enhancement was observed for the MMN elicited by 3200 Hz deviant tones among 4000 Hz standards. Also SRSs significantly increased with time and correlated with MMN amplitudes to the 3200 Hz deviants in both measurements.

Passive sound exposure induces rapid perceptual learning in musicians: event-related potential evidence

Musicians show enhanced auditory processing compared to nonmusicians. However, the neural basis underlying the effects of musical training on rapid plasticity in auditory processing has not been systematically studied. Here, the rapid (one session) learning-related plastic changes in event-related potential (ERP) responses for pitch and duration deviants between passive blocks were compared between musicians and nonmusicians. Passive blocks were interleaved with an active discrimination task. In addition to musicians having faster and stronger overall source activation for deviating sounds, source analysis revealed rapid plastic changes in the left and right temporal and left frontal sources that were present only in musicians. Source activation decreased in these areas even without focused attention. Furthermore, deviant-related ERP responses above the parietal areas decreased after the active task in both musicians and nonmusicians. Taken together, the results indicate enhanced rapid plasticity in sound change discrimination and perceptual learning in musicians when compared with nonmusicians.

The effect of native-language experience on the sensory-obligatory components, the P1-N1-P2 and the T-complex

The influence of native-language experience on sensory-obligatory auditory-evoked potentials (AEPs) was investigated in native-English and native-Polish listeners. AEPs were recorded to the first word in nonsense word pairs, while participants performed a syllable identification task to the second word in the pairs. Nonsense words contained phoneme sequence onsets (i.e., /pt/, /pət/, /st/ and /sət/) that occur in the Polish and English languages, with the exception that /pt/ at syllable onset is an illegal phonotactic form in English. P1-N1-P2 waveforms from fronto-central electrode sites were comparable in English and Polish listeners, even though, these same English participants were unable to distinguish the nonsense words having /pt/ and /pət/ onsets. The P1-N1-P2 complex indexed the temporal characteristics of the word stimuli in the same manner for both language groups. Taken together, these findings suggest that the fronto-central P1-N1-P2 complex reflects acoustic feature processing of speech and is not significantly influenced by exposure to the phoneme sequences of the native-language. In contrast, the T-complex from bilateral posterior temporal sites was found to index phonological as well as acoustic feature processing to the nonsense word stimuli. An enhanced negativity for the /pt/ cluster relative to its contrast sequence (i.e., /pət/) occurred only for the Polish listeners, suggesting that neural networks within non-primary auditory cortex may be involved in early cortical phonological processing.

The impact of neurodegeneration on network connectivity: a study of change detection in frontotemporal dementia

The neural response to unpredictable auditory events is suggested to depend on frontotemporal interactions. We used magnetoencephalography in patients with behavioral variant frontotemporal dementia to study change detection and to examine the impact of disease on macroscopic network connectivity underlying this core cognitive function. In patients, the amplitudes of auditory cortical responses to predictable standard tones were normal but were reduced for unpredictable deviant tones. Network connectivity, in terms of coherence among frontal, temporal, and parietal sources, was also abnormal in patients. In the beta frequency range, left frontotemporal coherence was reduced. In the gamma frequency range, frontal interhemispheric coherence was reduced whereas parietal interhemispheric coherence was enhanced. These results suggest impaired change detection resulting from dysfunctional frontotemporal interactions. They also provide evidence of a rostro-caudal reorganization of brain networks in disease. The sensitivity of magnetoencephalography to cortical network changes in behavioral variant frontotemporal dementia enriches the understanding of neurocognitive systems as well as showing potential for studies of experimental therapies for neurodegenerative disease.

Infants' brain responses for speech sound changes in fast multifeature MMN paradigm

OBJECTIVE

We investigated whether newborn speech-sound discrimination can be studied in 40 min using fast multifeature mismatch negativity (MMN) paradigm and do the results differ from those obtained with the traditional oddball paradigm.

METHODS

Newborns' MMN responses to five types of changes (consonant identity, F0, intensity, vowel duration and vowel identity) were recorded in the multifeature group (N=15) and vowel duration and vowel identity changes in the oddball group (N=13), after which the MMNs from both groups were compared with each others.

RESULTS

Statistically significant MMNs in the 190-600 ms time range from the stimulus onset were found for most change types in both paradigms. Newborn MMN responses were predominantly positive but a small number of participants elicited negative MMNs instead. MMN amplitudes did not differ between the multifeature and oddball groups.

CONCLUSIONS

Newborn speech-sound discrimination can be assessed in a short recording time using the fast multifeature paradigm.

SIGNIFICANCE

The paradigm presented here can be used to record extensive auditory discrimination profiles in newborns and assess development of speech-sound discrimination and its difficulties.

The neural basis of aberrant speech and audition in autism spectrum disorders

Autism spectrum disorders (ASD) are characterized by deficits in communication and social behavior and by narrow interests. Individuals belonging to this spectrum have abnormalities in various aspects of language, ranging from semantic-pragmatic deficits to the absence of speech. They also have aberrant perception, especially in the auditory domain, with both hypo- and hypersensitive features. Neurophysiological approaches with high temporal resolution have given novel insight into the processes underlying perception and language in ASD. Neurophysiological recordings, which are feasible for investigating infants and individuals with no speech, have shown that the representation of and attention to language has an abnormal developmental path in ASD. Even the basic mechanisms for fluent speech perception are degraded at a low level of neural speech analysis. Furthermore, neural correlates of perception and some traits typical of subgroups of individuals on this spectrum have helped in understanding the diversity on this spectrum.

Different kinds of bilinguals: different kinds of brains: the neural organisation of two languages in one brain

The aim of this study was to determine whether the type of bilingualism affects neural organisation. We performed identification experiments and mismatch negativity (MMN) registrations in Finnish and Swedish language settings to see, whether behavioural identification and neurophysiological discrimination of vowels depend on the linguistic context, and whether there is a difference between two kinds of bilinguals. The stimuli were two vowels, which differentiate meaning in Finnish, but not in Swedish. The results indicate that Balanced Bilinguals are inconsistent in identification performance, and they have a longer MMN latency. Moreover, their MMN amplitude is context-independent, while Dominant Bilinguals show a larger MMN in the Finnish context. These results indicate that Dominant Bilinguals inhibit the preattentive discrimination of native contrast in a context where the distinction is non-phonemic, but this is not possible for Balanced Bilinguals. This implies that Dominant Bilinguals have separate systems, while Balanced Bilinguals have one inseparable system.

Auditory-motor processing of speech sounds

The motor regions that control movements of the articulators activate during listening to speech and contribute to performance in demanding speech recognition and discrimination tasks. Whether the articulatory motor cortex modulates auditory processing of speech sounds is unknown. Here, we aimed to determine whether the articulatory motor cortex affects the auditory mechanisms underlying discrimination of speech sounds in the absence of demanding speech tasks. Using electroencephalography, we recorded responses to changes in sound sequences, while participants watched a silent video. We also disrupted the lip or the hand representation in left motor cortex using transcranial magnetic stimulation. Disruption of the lip representation suppressed responses to changes in speech sounds, but not piano tones. In contrast, disruption of the hand representation had no effect on responses to changes in speech sounds. These findings show that disruptions within, but not outside, the articulatory motor cortex impair automatic auditory discrimination of speech sounds. The findings provide evidence for the importance of auditory-motor processes in efficient neural analysis of speech sounds.

Fast reconfiguration of high-frequency brain networks in response to surprising changes in auditory input

How do human brain networks react to dynamic changes in the sensory environment? We measured rapid changes in brain network organization in response to brief, discrete, salient auditory stimuli. We estimated network topology and distance parameters in the immediate central response period, <1 s following auditory presentation of standard tones interspersed with occasional deviant tones in a mismatch-negativity (MMN) paradigm, using magnetoencephalography (MEG) to measure synchronization of high-frequency (gamma band; 33-64 Hz) oscillations in healthy volunteers. We found that global small-world parameters of the networks were conserved between the standard and deviant stimuli. However, surprising or unexpected auditory changes were associated with local changes in clustering of connections between temporal and frontal cortical areas and with increased interlobar, long-distance synchronization during the 120- to 250-ms epoch (coinciding with the MMN-evoked response). Network analysis of human MEG data can resolve fast local topological reconfiguration and more long-range synchronization of high-frequency networks as a systems-level representation of the brain's immediate response to salient stimuli in the dynamically changing sensory environment.

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.

Could audiovisual training be used to improve cognition in extremely low birth weight children?

AIM

To study whether a dyslexia remediation programme, Audilex, improves cognition in extremely low birth (ELBW) children.

METHODS

Six-year-old ELBW children were allocated to a 5-week training with Audilex or playing control computer games. Before and after intervention, auditory event-related brain potentials (ERP) to sound changes were recorded and reading related skills assessed. Primary outcome was the mismatch negativity (MMN) component of ERP. Secondary outcomes were Audilex Test (ability to perform the Audilex games), the reading skills after the intervention and 2 years later. Of eligible children, 39 (54%) consented and 22 (30%) completed the protocol.

RESULTS

The MMN responses to the frequency (p = 0.02) and duration deviants (p < 0.01) increased after Audilex training (n = 11), but not after control game playing (n = 11). Audilex Test performance was similar in both groups. The reading skills were similar after intervention and 2 years later; word reading score 59.7, 66.8 and 74.9 and comprehensive reading score 8.1, 8.8 and 9.4 in Audilex, Control and healthy class-mate children, respectively.

CONCLUSIONS

Although all children did not complete the protocol, the results suggest that training with Audilex dyslexia programme might be beneficial for enhancing neural-level sound discrimation and possibly reading skills in ELBW children. A larger trial is warranted.

Linguistic multifeature MMN paradigm for extensive recording of auditory discrimination profiles

We studied whether a multifeature mismatch negativity (MMN) paradigm using naturally produced speech stimuli is feasible for studies of auditory discrimination accuracy of adult participants. A naturally produced trisyllabic pseudoword was used in the paradigm, and MMNs were recorded to changes that were acoustic (changes in fundamental frequency or intensity) or potentially phonological (changes in vowel identity or vowel duration). All the different changes were presented in three different word segments (initial, middle, or final syllable). All changes elicited an MMN response, but the vowel duration change elicited a different response pattern than the other deviant types. Changes in vowel duration and identity also had an effect on MMN lateralization. Our results show that assessing speech sound discrimination of several features in word context is possible in a short recording time (30 min) with the multifeature paradigm.

Acoustic processing of temporally modulated sounds in infants: evidence from a combined near-infrared spectroscopy and EEG study

Speech perception requires rapid extraction of the linguistic content from the acoustic signal. The ability to efficiently process rapid changes in auditory information is important for decoding speech and thereby crucial during language acquisition. Investigating functional networks of speech perception in infancy might elucidate neuronal ensembles supporting perceptual abilities that gate language acquisition. Interhemispheric specializations for language have been demonstrated in infants. How these asymmetries are shaped by basic temporal acoustic properties is under debate. We recently provided evidence that newborns process non-linguistic sounds sharing temporal features with language in a differential and lateralized fashion. The present study used the same material while measuring brain responses of 6 and 3 month old infants using simultaneous recordings of electroencephalography (EEG) and near-infrared spectroscopy (NIRS). NIRS reveals that the lateralization observed in newborns remains constant over the first months of life. While fast acoustic modulations elicit bilateral neuronal activations, slow modulations lead to right-lateralized responses. Additionally, auditory-evoked potentials and oscillatory EEG responses show differential responses for fast and slow modulations indicating a sensitivity for temporal acoustic variations. Oscillatory responses reveal an effect of development, that is, 6 but not 3 month old infants show stronger theta-band desynchronization for slowly modulated sounds. Whether this developmental effect is due to increasing fine-grained perception for spectrotemporal sounds in general remains speculative. Our findings support the notion that a more general specialization for acoustic properties can be considered the basis for lateralization of speech perception. The results show that concurrent assessment of vascular based imaging and electrophysiological responses have great potential in the research on language acquisition.

Plasticity and imaging research in healthy aging: core ideas and profile of the International Normal Aging and Plasticity Imaging Center (INAPIC)

The key objective of the International Normal Aging and Plasticity Imaging Center (INAPIC) at the University of Zürich is to facilitate research on normal healthy behavioral and neural development and aging to explore the potential for plasticity and compensation across the lifespan. The INAPIC invites international research groups to submit proposals for collaborative projects on these subjects. It is unique in Europe in giving partner groups 'plug and play' access to state-of-the-art neuroimaging techniques, technical support, and assistance in data collection. This article introduces the core ideas of the INAPIC, its key research areas, and the available infrastructure.

Face recognition in Asperger syndrome: a study on EEG spectral power changes

EEG reactions in emotional face recognition were studied in five participants with Asperger syndrome (AS) and seven control subjects. Control subjects showed a spectral power increase following the stimulus onset in two time-frequency intervals-(1) 150-300ms in the 1-16Hz frequency range and (2) 300-650ms in the 1-8Hz range. Also, alpha/beta desynchronization occurred 400-1000ms after the stimulus onset with maximal amplitude in the posterior region. Theta synchronization (4-8Hz) was weaker in the AS group than in the control group, but beta2 desynchronization was stronger in the AS group. The results were interpreted in terms of automatic and voluntary control of perception.

It's about Time

The purpose of this review/opinion paper is to argue that human cognitive neuroscience has focused too little attention on how the brain may use time and time-based coding schemes to represent, process, and transfer information within and across brain regions. Instead, the majority of cognitive neuroscience studies rest on the assumption of functional localization. Although the functional localization approach has brought us a long way toward a basic characterization of brain functional organization, there are methodological and theoretical limitations of this approach. Further advances in our understanding of neurocognitive function may come from examining how the brain performs computations and forms transient functional neural networks using the rich multi-dimensional information available in time. This approach rests on the assumption that information is coded precisely in time but distributed in space; therefore, measures of rapid neuroelectrophysiological dynamics may provide insights into brain function that cannot be revealed using localization-based approaches and assumptions. Space is not an irrelevant dimension for brain organization; rather, a more complete understanding of how brain dynamics lead to behavior dynamics must incorporate how the brain uses time-based coding and processing schemes.

Pre-attentive and attentive processing of French vowels

This study aimed at investigating the effects of acoustic distance and of speaker variability on the pre-attentive and attentive perception of French vowels by French adult speakers. The electroencephalogram (EEG) was recorded while participants watched a silent movie (Passive condition) and discriminated deviant vowels (Active condition). The auditory sequence included 4 French vowels, /u/ (standard) and /o/, /y/ and /ø/ as deviants, produced by 3 different speakers. As the vowel /o/ is closer to /u/ than the other deviants in acoustic distance, we predicted smaller mismatch negativity (MMN) and smaller N1 component, as well as higher error rate and longer reaction times. Results were in line with these predictions. Moreover, the MMN was elicited by all deviant vowels independently of speaker variability. By contrast, the Vowel by Speaker interaction was significant in the Active listening condition thereby showing that subtle within-category differences are processed at the attentive level. These results suggest that while vowels are categorized pre-attentively according to phonemic representations and independently of speaker variability, participants are sensitive to between-speaker differences when they focus attention on vowel processing.