Right cerebral motor areas that support accurate speech production following damage to cerebellar speech areas

Specific regions of the cerebellum are activated when neurologically intact adults speak, and cerebellar damage can impair speech production early after stroke, but how the brain supports accurate speech production years after cerebellar damage remains unknown. We investigated this in patients with cerebellar lesions affecting regions that are normally recruited during speech production. Functional MRI activation in these patients, measured during various single word production tasks, was compared to that of neurologically intact controls, and patient controls with lesions that spared the cerebellar speech production regions. Our analyses revealed that, during a range of speech production tasks, patients with damage to cerebellar speech production regions had greater activation in the right dorsal premotor cortex (r-PMd) and right supplementary motor area (r-SMA) compared to neurologically intact controls. The loci of increased activation in cerebral motor speech areas motivate future studies to delineate the functional contributions of different parts of the speech production network, and test whether non-invasive stimulation to r-PMd and r-SMA facilitates speech recovery after cerebellar stroke

Transcallosal connection patterns of opposite dorsal premotor regions support a lateralized specialization for action and perception

Lateralization of higher brain functions requires that a dominant hemisphere collects relevant information from both sides. The right dorsal premotor cortex (PMd), particularly implicated in visuomotor transformations, was hypothesized to be optimally located to converge visuospatial information from both hemispheres for goal-directed movement. This was assessed by probabilistic tractography and a novel analysis enabling group comparisons of whole-brain connectivity distributions of the left and right PMd in standard space (16 human subjects). The resulting dominance of contralateral PMd connections was characterized by right PMd connections with left visual and parietal areas, indeed supporting a dominant role in visuomotor transformations, while the left PMd showed dominant contralateral connections with the frontal lobe. Ipsilateral right PMd connections were also stronger with posterior parietal regions, relative to the left PMd connections, while ipsilateral connections of the left PMd were stronger with, particularly, the anterior cingulate, the ventral premotor and anterior parietal cortex. The pattern of dominant right PMd connections thus points to a specific role in guiding perceptual information into the motor system, while the left PMd connections are consistent with action dominance based on a lead in motor intention and fine precision skills

Exploring the neurobiology of reading through non-invasive brain stimulation: A review

Non-invasive brain stimulation (NIBS) has gained increasing popularity as a modulatory tool for drawing causal inferences and exploring task-specific network interactions. Yet, a comprehensive synthesis of reading-related NIBS studies is still missing. We fill this gap by synthesizing the results of 78 NIBS studies investigating the causal involvement of brain regions for reading processing, and then link these results to a neurobiological model of reading. The included studies provide evidence for a functional-anatomical double dissociation for phonology versus semantics during reading-related processes within left inferior frontal and parietal areas. Additionally, the posterior parietal cortex and the anterior temporal lobe are identified as critical regions for reading-related processes. Overall, the findings provide some evidence for a dual-stream neurobiological model of reading, in which a dorsal stream (left temporo-parietal and inferior frontal areas) processes unfamiliar words and pseudowords, and a ventral stream (left occipito-temporal and inferior frontal areas, with assistance from the angular gyrus and the anterior temporal lobe) processes known words. However, individual differences in reading abilities and strategies, as well as differences in stimulation parameters, may impact the neuromodulatory effects induced by NIBS. We emphasize the need to investigate task-specific network interactions in future studies by combining NIBS with neuroimaging

Die vergessene Hemisphäre: rechtshemisphärische Beiträge zu modalitäts-unabhängigen phonologischen Aspekten der Sprachverarbeitung im gesunden menschlichen Gehirn

This thesis investigates the representation of phonological language aspects in the healthy human brain, especially the contribution of the right hemisphere. Using functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS), it is demonstrated that the left and right supramarginal gyri are essential for phonological processing. It is also shown that the left as well as the right posterior inferior frontal gyri contribute to efficient phonological decisions. Finally, an fMRI study reveals a frontal network for phonological aspects of language production. These results demonstrate a contribution of both hemispheres to efficient phonological aspects of language comprehension as well as production. Together, these results question the notion of a left-dominant network of brain regions for language processing.In dieser Arbeit wurde die Repräsentation phonologischer Sprachaspekte im gesunden Gehirn untersucht. Von besonderem Interesse war der Beitrag der rechten Hemisphäre. Dabei wurde mit funktioneller Magnetresonanztomographie (fMRT) und transkranieller Magnetstimulation die Relevanz des linken und rechten Gyrus supramarginalis für phonologische Sprachaspekte nachgewiesen. Weiterhin wurde gezeigt, dass der linke und rechte posteriore Gyrus frontalis inferior ebenfalls essentiell für die phonologische Verarbeitung sind. Abschließend wurde mittels fMRT ein frontales Netzwerk identifiziert, das an phonologischen Aspekten der Sprachproduktion beteiligt ist. Insgesamt zeigen die vorliegenden Ergebnisse, dass Areale beider Hemisphären gleichermaßen relevant für effiziente phonologische Entscheidungen im gesunden Gehirn sind. Dies stellt die bisher in der Literatur vorherrschende Dominanz der linken Hemisphäre für die Verarbeitung von Sprache in Frage

Functionally distinct contributions of the anterior and posterior putamen during sublexical and lexical reading.

Previous studies have investigated orthographic-to-phonological mapping during reading by comparing brain activation for (1) reading words to object naming, or (2) reading pseudowords (e.g., "phume") to words (e.g., "plume"). Here we combined both approaches to provide new insights into the underlying neural mechanisms. In fMRI data from 25 healthy adult readers, we first identified activation that was greater for reading words and pseudowords relative to picture and color naming. The most significant effect was observed in the left putamen, extending to both anterior and posterior borders. Second, consistent with previous studies, we show that both the anterior and posterior putamen are involved in articulating speech with greater activation during our overt speech production tasks (reading, repetition, object naming, and color naming) than silent one-back-matching on the same stimuli. Third, we compared putamen activation for words versus pseudowords during overt reading and auditory repetition. This revealed that the anterior putamen was most activated by reading pseudowords, whereas the posterior putamen was most activated by words irrespective of whether the task was reading words or auditory word repetition. The pseudoword effect in the anterior putamen is consistent with prior studies that associated this region with the initiation of novel sequences of movements. In contrast, the heightened word response in the posterior putamen is consistent with other studies that associated this region with "memory guided movement." Our results illustrate how the functional dissociation between the anterior and posterior putamen supports sublexical and lexical processing during reading

Brain activation during non-habitual speech production: Revisiting the effects of simulated disfluencies in fluent speakers

Over the past decades, brain imaging studies in fluently speaking participants have greatly advanced our knowledge of the brain areas involved in speech production. In addition, complementary information has been provided by investigations of brain activation patterns associated with disordered speech. In the present study we specifically aimed to revisit and expand an earlier study by De Nil and colleagues, by investigating the effects of simulating disfluencies on the brain activation patterns of fluent speakers during overt and covert speech production. In contrast to the De Nil et al. study, the current findings show that the production of voluntary, self-generated disfluencies by fluent speakers resulted in increased recruitment and activation of brain areas involved in speech production. These areas show substantial overlap with the neural networks involved in motor sequence learning in general, and learning of speech production, in particular. The implications of these findings for the interpretation of brain imaging studies on disordered and non-habitual speech production are discussed

Phonetic Encoding, Verbal Working Memory and The Role of Broca's Area

Informatics Life-Sciences InstituteEven though Broca's area has been associated with speech and language processing since the 19th century, the exact role that it plays is still a matter of debate. Recent models on the neuroanatomical substrates of language have assigned Broca's area to different processes: syllabification (Indefrey and Levelt 2004), articulatory code storage (Hickok and Poeppel 2004) and verbal working memory (Chein and Fiez 2001; Chein et al. 2002). The subject of this doctoral dissertation, is to examine language production and disambiguate the role of Broca's area. This issue was addressed in a series of functional magnetic resonance imaging studies (fMRI) involving speech production, where the phonological properties of pseudowords were manipulated in a way that differentiated between syllabification and articulatory code generation. The load on verbal working memory was also changed. The behaviour of Broca's area was then examined in response to these manipulations to determine the dependence of the observed results on the different levels of processing and verbal working memory. The results from the present studies suggest that the dorsal premotor cortex has a consistent role in articulatory code generation irrespective of verbal working memory demands. In contrast, Broca's area, specifically Brodmann area 44, showed a main effect of phonetic encoding only during delayed response tasks. Interestingly, area BA44 was also found to be functionally segregated between the dorsal and ventral part. The dorsal part was sensitive to articulatory and phonological load, such as stimulus length. The ventral part on the other hand was sensitive to sub-lexical stimulus properties, but only during delayed response trials. These findings suggest that BA44 is not a homogeneous region, but it is divided into a dorsal premotor and a ventral prefrontal part. These results add another dimension of complexity to the study of Broca's area, its functional segregation and its role in language production

Motor skill learning between selection and execution.

Learning motor skills evolves from the effortful selection of single movement elements to their combined fast and accurate production. We review recent trends in the study of skill learning which suggest a hierarchical organization of the representations that underlie such expert performance, with premotor areas encoding short sequential movement elements (chunks) or particular component features (timing/spatial organization). This hierarchical representation allows the system to utilize elements of well-learned skills in a flexible manner. One neural correlate of skill development is the emergence of specialized neural circuits that can produce the required elements in a stable and invariant fashion. We discuss the challenges in detecting these changes with fMRI

Identifying Individual Differences in the Neural Correlates of Language Processing Using fMRI

Mapping language functions in the brain is of profound theoretical and clinical interest. The aim of the current Ph.D. project was to develop an fMRI paradigm to assesses different language processes (i.e., phonological, semantic, sentence processing) and modalities (listening, reading, repetition) in a stimulus-driven manner, keeping non-linguistic task demands to a minimum. Cortical activations and functional connectivity patterns were largely in line with previous research, validating the suitability of the paradigm for localizing different language processes. The first empirical chapter of the thesis investigated sentence comprehension in listening and reading, which elicited largely overlapping activations for the two modalities and for semantic and syntactic integration in the left anterior temporal lobe (ATL). Functional connectivity of the left ATL with other parts of the cortical language network differed between the modalities and processes. The second empirical chapter explored individual differences in brain activity in relation to verbal ability. Results supported the notion of more extended as well as stronger activations during language processing in individuals with higher verbal ability, possibly reflecting enhanced processing. The third empirical chapter further investigated individual differences in brain activity, focusing on lateralization in activity as a fundamental principle of how language processing is functionally organized in the brain. Degrees of left-lateralization differed significantly between language processes and were positively related to behaviorally assessed language lateralization. Furthermore, the results provided new evidence supporting a positive relationship between left-lateralization and verbal ability. The thesis concludes with a discussion of the significance of the results with regard to general principles of brain functioning and outlines potential clinical implications

Skill learning strengthens cortical representations of motor sequences.

Motor-skill learning can be accompanied by both increases and decreases in brain activity. Increases may indicate neural recruitment, while decreases may imply that a region became unimportant or developed a more efficient representation of the skill. These overlapping mechanisms make interpreting learning-related changes of spatially averaged activity difficult. Here we show that motor-skill acquisition is associated with the emergence of highly distinguishable activity patterns for trained movement sequences, in the absence of average activity increases. During functional magnetic resonance imaging, participants produced either four trained or four untrained finger sequences. Using multivariate pattern analysis, both untrained and trained sequences could be discriminated in primary and secondary motor areas. However, trained sequences were classified more reliably, especially in the supplementary motor area. Our results indicate skill learning leads to the development of specialized neuronal circuits, which allow the execution of fast and accurate sequential movements without average increases in brain activity. DOI:http://dx.doi.org/10.7554/eLife.00801.001