Phoneme perception in a neonate with a left sylvian infarct

Affective Prosody and Its Impact on the Neurology of Language, Depression, Memory and Emotions

Based on the seminal publications of Paul Broca and Carl Wernicke who established that aphasic syndromes (disorders of the verbal-linguistic aspects of communication) were predominantly the result of focal left-hemisphere lesions, "language" is traditionally viewed as a lateralized function of the left hemisphere. This, in turn, has diminished and delayed the acceptance that the right hemisphere also has a vital role in language, specifically in modulating affective prosody, which is essential for communication competency and psychosocial well-being. Focal lesions of the right hemisphere may result in disorders of affective prosody (aprosodic syndromes) that are functionally and anatomically analogous to the aphasic syndromes that occur following focal left-hemisphere lesions. This paper will review the deductive research published over the last four decades that has elucidated the neurology of affective prosody which, in turn, has led to a more complete and nuanced understanding of the neurology of language, depression, emotions and memory. In addition, the paper will also present the serendipitous clinical observations (inductive research) and fortuitous inter-disciplinary collaborations that were crucial in guiding and developing the deductive research processes that culminated in the concept that primary emotions and related display behaviors are a lateralized function of the right hemisphere and social emotions, and related display behaviors are a lateralized function of the left hemisphere.

Handedness Development: A Model for Investigating the Development of Hemispheric Specialization and Interhemispheric Coordination

The author presents his perspective on the character of science, development, and handedness and relates these to his investigations of the early development of handedness. After presenting some ideas on what hemispheric specialization of function might mean for neural processing and how handedness should be assessed, the neuroscience of control of the arms/hands and interhemispheric communication and coordination are examined for how developmental processes can affect these mechanisms. The author’s work on the development of early handedness is reviewed and placed within a context of cascading events in which different forms of handedness emerge from earlier forms but not in a deterministic manner. This approach supports a continuous rather than categorical distribution of handedness and accounts for the predominance of right-handedness while maintaining a minority of left-handedness. Finally, the relation of the development of handedness to the development of several language and cognitive skills is examined.

Left temporal plane growth predicts language development in newborns with congenital heart disease

Congenital heart defects are the most common congenital anomalies, accounting for a third of all congenital anomaly cases. While surgical correction dramatically improved survival rates, the lag behind normal neurodevelopment appears to persist. Deficits in higher cognitive functions are particularly common, including developmental delay in communication and oral-motor apraxia. It remains unclear whether the varying degree of cognitive developmental delay is reflected in variability in brain growth patterns. To answer this question, we aimed to investigate whether the rate of regional brain growth is correlated with later life neurodevelopment. Forty-four newborns were included in our study, of whom 33 were diagnosed with dextro-transposition of the great arteries and 11 with other forms of severe congenital heart defects. During the first month of life, neonates underwent corrective or palliative cardiovascular bypass surgery, pre- and postoperative cerebral MRI were performed 18.7 ± 7.03 days apart. MRI was performed in natural sleep on a 3.0 T scanner using an 8-channel head coil, fast spin-echo T2-weighted anatomical sequences were acquired in three planes. Based on the principles of deformation-based morphometry, we calculated brain growth rate maps reflecting average daily growth occurring between pre- and postoperative brain images. An explorative, whole-brain, threshold-free cluster enhancement analysis revealed strong correlation between the growth rate of the Heschl's gyrus, anterior planum temporale and language score at 12 months of age, corrected for demographic variables (P = 0.018, t = 5.656). No significant correlation was found between brain growth rates and motor or cognitive scores. Post hoc analysis showed that the length of hospitalization interacted with this correlation, longer hospitalization resulted in faster enlargement of the internal CSF spaces. Our longitudinal cohort study provides evidence for the early importance of left-dominant perisylvian regions in auditory and language development before direct postnatal exposure to native language. In congenital heart disease patients, the perioperative period results in a critical variability of brain growth rate in this region, which is a reliable neural correlate of language development at 1 year of age.

Developmental sequelae and neurophysiologic substrates of sensory seeking in infant siblings of children with autism spectrum disorder

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Infant siblings of children with autism (Sibs-ASD) display elevated sensory seeking.

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Sibs-ASD who will be diagnosed with ASD show the highest levels of sensory seeking.

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Sensory seeking at 18 months predicts future social symptomatology in Sibs-ASD.

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The effect of seeking on social symptomatology is explained by reduced social orienting.

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Atypical frontal asymmetry may underlie early differences in sensory seeking.

It has been proposed that early differences in sensory responsiveness arise from atypical neural function and produce cascading effects on development across domains. This longitudinal study prospectively followed infants at heightened risk for autism spectrum disorder (ASD) based on their status as younger siblings of children diagnosed with ASD (Sibs-ASD) and infants at relatively lower risk for ASD (siblings of typically developing children; Sibs-TD) to examine the developmental sequelae and possible neurophysiological substrates of a specific sensory response pattern: unusually intense interest in nonsocial sensory stimuli or “sensory seeking.” At 18 months, sensory seeking and social orienting were measured with the Sensory Processing Assessment, and a potential neural signature for sensory seeking (i.e., frontal alpha asymmetry) was measured via resting state electroencephalography. At 36 months, infants’ social symptomatology was assessed in a comprehensive diagnostic evaluation. Sibs-ASD showed elevated sensory seeking relative to Sibs-TD, and increased sensory seeking was concurrently associated with reduced social orienting across groups and resting frontal asymmetry in Sibs-ASD. Sensory seeking also predicted later social symptomatology. Findings suggest that sensory seeking may produce cascading effects on social development in infants at risk for ASD and that atypical frontal asymmetry may underlie this atypical pattern of sensory responsiveness.

Early changes in brain structure correlate with language outcomes in children with neonatal encephalopathy

Global patterns of brain injury correlate with motor, cognitive, and language outcomes in survivors of neonatal encephalopathy (NE). However, it is still unclear whether local changes in brain structure predict specific deficits. We therefore examined whether differences in brain structure at 6 months of age are associated with neurodevelopmental outcomes in this population. We enrolled 32 children with NE, performed structural brain MR imaging at 6 months, and assessed neurodevelopmental outcomes at 30 months. All subjects underwent T1-weighted imaging at 3 T using a 3D IR-SPGR sequence. Images were normalized in intensity and nonlinearly registered to a template constructed specifically for this population, creating a deformation field map. We then used deformation based morphometry (DBM) to correlate variation in the local volume of gray and white matter with composite scores on the Bayley Scales of Infant and Toddler Development (Bayley-III) at 30 months. Our general linear model included gestational age, sex, birth weight, and treatment with hypothermia as covariates. Regional brain volume was significantly associated with language scores, particularly in perisylvian cortical regions including the left supramarginal gyrus, posterior superior and middle temporal gyri, and right insula, as well as inferior frontoparietal subcortical white matter. We did not find significant correlations between regional brain volume and motor or cognitive scale scores. We conclude that, in children with a history of NE, local changes in the volume of perisylvian gray and white matter at 6 months are correlated with language outcome at 30 months. Quantitative measures of brain volume on early MRI may help identify infants at risk for poor language outcomes.

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Global volume loss after neonatal brain injury results in poorer language outcome.

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Variability in language correlates specifically with left perisylvian brain volume.

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Changes in regional brain volume are not correlated with motor or cognitive outcome.

Language recovery after left hemispherotomy for Rasmussen encephalitis

PURPOSE

Hemispherotomy (H) is the gold standard treatment to cure epilepsy in Rasmussen encephalitis (RE). Linguistic prognosis after surgery remains the main issue when the dominant hemisphere is involved. The topic of the present research is to specify the long-term linguistic profile of the right hemisphere after left dominant H for RE.

METHODS

We followed 6 children 8.4 to 14.6 years of age who underwent left H for RE. Preoperatively, four children experienced aphasia, but for two, worsening occurred after surgery. Age at H ranged from 4.1 to 8.4 years. The mean duration of epilepsy was 1.2 years and 5.6 years for follow-up. Neuropsychological evaluation included longitudinal follow-up of intellectual efficiency measurement and a long-term outcome of language using various components of receptive and expressive oral speech with computerized tasks.

KEY FINDINGS

Preoperatively, verbal comprehension index (VCI) was dramatically decreased in 4/6 patients, and performance reasoning index (PRI) was low in 5/6 participants, demonstrating a global impact of RE itself. Postoperatively, all children recovered sufficiently to attend a regular VCI (above 70) in a mean of 5 years after H, and 5/6 recovered normal or adapted school. There was a dissociation in favor of VCI, while PRI decreased in 5/6 patients. We found a specific linguistic profile for these children recovering language in the right hemisphere: normal verbal comprehension, and weakness of grammatical judgment, word repetition, statement production, semantic verbal fluency and metaphonological abilities. Language recovery scores were statistically correlated with those of Working Memory Index.

SIGNIFICANCE

This study emphasizes for the first time the ability of the right hemisphere to functionally reorganize language over a long period of time following left H for RE. Syntactic abilities and phonology remain low and support the hypothesis of an early left hemispheric specialization. Nevertheless, lexico-semantic processes recover in the right hemisphere that could reflect a pre-existing potential of both hemispheres. Our results support a decision to proceed to H in classical left RE disease until the late childhood even if there is no complete aphasia before surgery. These data should be taken in account in the overall postoperative follow-up and rehabilitation strategy.

Adaptive mechanisms of developing brain: cerebral lateralization in the prematurely-born

Preterm birth results in alterations in neural connectivity, but the impact of prematurity on the functional organization of the developing brain has yet to be explored. To test the hypothesis that preterm birth alters cortical organization during the late second and third trimesters of gestation, we interrogated cerebral lateralization at rest in 26 very preterm subjects (birth weight 500-1500g) with no evidence of brain injury and 25 healthy term control subjects at term equivalent age. Employing an unbiased voxel-based measure of functional connectivity, these data demonstrated that cerebral lateralization is impaired in the prematurely-born. At term equivalent age, preterm neonates showed significantly less lateralization in regions subserving both receptive and expressive language, left Brodmann (BA) areas insula-BA22-BA21 and L BA45-BA47 (p<0.05 corrected for multiple comparisons for both). Exploratory region of interest analyses demonstrated significantly less inter-hemispheric connectivity from L BA22 to R BA22 in preterm infants compared to term controls (p<0.005) and from R BA22 to its homolog (p<0.005). L BA22, Wernicke's area, was more strongly connected to R BA39, foreshadowing neural networks for language in preterm subjects at school age, adolescence and young adulthood. For these very preterm neonates born at less than 30weeks' PMA, the degree of prematurity had no influence on lateralization in these differential regions.

Unattentive speech processing is influenced by orthographic knowledge: evidence from mismatch negativity

How far can acquired knowledge such as orthographic knowledge affect pre-existing abilities such as speech perception? This controversial issue was addressed by investigating the automaticity of the influence of orthographic knowledge on speech processing. Many studies demonstrated this influence in active, lexico-semantic speech processing tasks. However, it has never been observed when speech is unattended. Here, the Mismatch Negativity (MMN), an automatic index of experience-dependent auditory traces, was recorded in an unattended oddball paradigm manipulating the orthographic congruency between frequent and deviant spoken riming words. Both orthographically congruent and incongruent deviant words elicited a typical MMN over the fronto-central regions, with a stronger response in the incongruent condition. The finding showed that the orthographic dimension of spoken words influences a physiological marker of speech processing although participants were required not to attend to the auditory input. This provides evidence for an impact of acquiring a written code on speech processing.

Attitudinal prosody: what we know and directions for future study

Prosodic aspects of speech such as pitch, duration and amplitude constitute nonverbal cues that supplement or modify the meaning of the spoken word, to provide valuable clues as to a speakers' state of mind. It can thus indicate what emotion a person is feeling (emotional prosody), or their attitude towards an event, person or object (attitudinal prosody). Whilst the study of emotional prosody has gathered pace, attitudinal prosody now deserves equal attention. In social cognition, understanding attitudinal prosody is important in its own right, since it can convey powerful constructs such as confidence, persuasion, sarcasm and superiority. In this review, it is examined what prosody is, how it conveys attitudes, and which attitudes prosody can convey. The review finishes by considering the neuroanatomy associated with attitudinal prosody, and put forward the hypothesis that this cognition is mediated by the right cerebral hemisphere, particularly posterior superior lateral temporal cortex, with an additional role for the basal ganglia, and limbic regions such as the medial prefrontal cortex and amygdala. It is suggested that further exploration of its functional neuroanatomy is greatly needed, since it could provide valuable clues about the value of current prosody nomenclature and its separability from other types of prosody at the behavioural level.

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.

Functional hemispheric specialization in processing phonemic and prosodic auditory changes in neonates

This study focuses on the early cerebral base of speech perception by examining functional lateralization in neonates for processing segmental and suprasegmental features of speech. For this purpose, auditory evoked responses of full-term neonates to phonemic and prosodic contrasts were measured in their temporal area and part of the frontal and parietal areas using near-infrared spectroscopy (NIRS). Stimuli used here were phonemic contrast /itta/ and /itte/ and prosodic contrast of declarative and interrogative forms /itta/ and /itta?/. The results showed clear hemodynamic responses to both phonemic and prosodic changes in the temporal areas and part of the parietal and frontal regions. In particular, significantly higher hemoglobin (Hb) changes were observed for the prosodic change in the right temporal area than for that in the left one, whereas Hb responses to the vowel change were similarly elicited in bilateral temporal areas. However, Hb responses to the vowel contrast were asymmetrical in the parietal area (around supra marginal gyrus), with stronger activation in the left. These results suggest a specialized function of the right hemisphere in prosody processing, which is already present in neonates. The parietal activities during phonemic processing were discussed in relation to verbal-auditory short-term memory. On the basis of this study and previous studies on older infants, the developmental process of functional lateralization from birth to 2 years of age for vowel and prosody was summarized.

Identifying cortical lateralization of speech processing in infants using near-infrared spectroscopy

We investigate the utility of near-infrared spectroscopy (NIRS) as an alternative technique for studying infant speech processing. NIRS is an optical imaging technology that uses relative changes in total hemoglobin concentration and oxygenation as an indicator of neural activation. Procedurally, NIRS has the advantage over more common methods (e.g., fMRI) in that it can be used to study the neural responses of behaviorally active infants. Older infants (aged 6-9 months) were allowed to sit on their caretakers' laps during stimulus presentation to determine relative differences in focal activity in the temporal region of the brain during speech processing. Results revealed a dissociation of sensory-specific processing in two cortical regions, the left and right temporal lobes. These findings are consistent with those obtained using other neurophysiological methods and point to the utility of NIRS as a means of establishing neural correlates of language development in older (and more active) infants.

Neurology of affective prosody and its functional-anatomic organization in right hemisphere

Unlike the aphasic syndromes, the organization of affective prosody in brain has remained controversial because affective-prosodic deficits may occur after left or right brain damage. However, different patterns of deficits are observed following left and right brain damage that suggest affective prosody is a dominant and lateralized function of the right hemisphere. Using the Aprosodia Battery, which was developed to differentiate left and right hemisphere patterns of affective-prosodic deficits, functional-anatomic evidence is presented in patients with focal ischemic strokes to support the concepts that (1) affective prosody is a dominant and lateralized function of the right hemisphere, (2) the intrahemispheric organization of affective prosody in the right hemisphere, with the partial exception of Repetition, is analogous to the organization of propositional language in the left hemisphere and (3) the aprosodic syndromes are cortically based as part of evolutionary adaptations underlying human language and communication.

Nature and nurture in language acquisition: anatomical and functional brain-imaging studies in infants

Speech processing in adults relies on precise and specialized networks, located primarily in the left hemisphere. Behavioral studies in infants indicate that a considerable amount of language learning already takes place in the first year of life in the domains of phonology, prosody and word segmentation. Thanks to neuroimaging, we can move beyond behavioral methods and examine how the infant brain processes verbal stimuli before learning. These studies reveal a structural and functional organization close to what is described in adults and suggest a strong bias for speech processing in these regions that might guide infants as they discover the properties of their native language, although no evidence can be provided as yet for speech specificity of such networks. This review is part of the INMED/TINS special issue "Nature and nurture in brain development and neurological disorders", based on presentations at the annual INMED/TINS symposium (http://inmednet.com/).

The right hemisphere of sleeping infant perceives sentential prosody

Behavioral studies proposed that prosodic information in speech sounds plays important roles for human infants to acquire their native languages. Here, we examined the neural basis of prosodic processing in 3-month-old infants. In order to obtain hemodynamic responses with high signal-to-noise ratio, we used near-infrared optical topography in the infants while they were in quiet sleep. First, we observed bilateral activation under each of the normal and flattened speech conditions. The flattened speech sound was created by eliminating changes in the pitch contours of the original utterance. In a direct comparison between the two conditions, the right temporoparietal region showed more prominent activation to normal speech sounds than to flattened speech sounds. This result demonstrates that the localized region of the right hemisphere in 3-month-old infant is involved in the processing of pitch contours. Our findings suggest that prosodic processing in the right hemisphere may facilitate the acquisition of lexical or syntactic knowledge in the early stages of language development.

Infant speech perception bootstraps word learning

By their first birthday, infants can understand many spoken words. Research in cognitive development has long focused on the conceptual changes that accompany word learning, but learning new words also entails perceptual sophistication. Several developmental steps are required as infants learn to segment, identify and represent the phonetic forms of spoken words, and map those word forms to different concepts. We review recent research on how infants' perceptual systems unfold in the service of word learning, from initial sensitivity for speech to the learning of language-specific sound patterns. Building on a recent theoretical framework and emerging new methodologies, we show how speech perception is crucial for word learning, and suggest that it bootstraps the development of a separate but parallel phonological system that links sound to meaning.

Common Neural Basis for Phoneme Processing in Infants and Adults

Investigating the degree of similarity between infants' and adults' representation of speech is critical to our understanding of infants' ability to acquire language. Phoneme perception plays a crucial role in language processing, and numerous behavioral studies have demonstrated similar capacities in infants and adults, but are these subserved by the same neural substrates or networks? In this article, we review event-related potential (ERP) results obtained in infants during phoneme discrimination tasks and compare them to results from the adult literature. The striking similarities observed both in behavior and ERPs between initial and mature stages suggest a continuity in processing and neural structure. We argue that infants have access at the beginning of life to phonemic representations, which are modified without training or implicit instruction, but by the statistical distributions of speech input in order to converge to the native phonemic categories.