Facilitation of speech repetition accuracy by theta burst stimulation of the left posterior inferior frontal gyrus

Aberrant modulation of broadband neural oscillations reflects vocal sensorimotor deficits in post-stroke aphasia

OBJECTIVE

The present study investigated the neural oscillatory correlates of impaired vocal sensorimotor control in left-hemisphere stroke.

METHODS

Electroencephalography (EEG) signals were recorded from 34 stroke and 46 control subjects during speech vowel vocalization and listening tasks under normal and pitch-shifted auditory feedback.

RESULTS

Time-frequency analyses revealed aberrantly decreased theta (4-8 Hz) and increased gamma band (30-80 Hz) power in frontal and posterior parieto-occipital regions as well as reduced alpha (8-13 Hz) and beta (13-30 Hz) desynchronization over sensorimotor areas before speech vowel vocalization in left-hemisphere stroke compared with controls. Subjects with the stroke also presented with aberrant modulation of broadband (4-80 Hz) neural oscillations over sensorimotor regions after speech vowel onset during vocalization and listening under normal and altered auditory feedback. We found that the atypical pattern of broadband neural oscillatory modulation was correlated with diminished vocal feedback error compensation behavior and the severity of co-existing language-related aphasia symptoms associated with left-hemisphere stroke.

CONCLUSIONS

These findings indicate complex interplays between the underlying mechanisms of speech and language and their deficits in post-stroke aphasia.

SIGNIFICANCE

Our data motivate the notion of studying neural oscillatory dynamics as a critical component for the examination of speech and language disorders in post-stroke aphasia.

Feasibility of intermediate theta burst stimulation as sham control in therapeutic transcranial magnetic stimulation studies

A major challenge in Transcranial Magnetic Stimulation trials is that of an inefficient sham protocol. This could potentially amplify the gap in behavioral outcomes following true and control treatments. Intermediate theta-burst stimulation (imTBS) is a promising sham alternative since it uses actual TMS pulses, thus mimicking the sensory effects of stimulation without producing physiological aftereffects. Here, we critically review controlled experiments that have examined physiological and behavioral aftereffects following imTBS with the intention to further investigate what appears to be a promising sham control modality for TBS studies.

The left inferior frontal gyrus is causally linked to vocal feedback control: evidence from high-definition transcranial alternating current stimulation

Current models of speech motor control propose a role for the left inferior frontal gyrus (IFG) in feedforward control of speech production. There is evidence, however, that has implicated the functional relevance of the left IFG for the neuromotor processing of vocal feedback errors. The present event-related potential (ERP) study examined whether the left IFG is causally linked to auditory feedback control of vocal production with high-definition transcranial alternating current stimulation (HD-tACS). After receiving active or sham HD-tACS over the left IFG at 6 or 70 Hz, 20 healthy adults vocalized the vowel sounds while hearing their voice unexpectedly pitch-shifted by ±200 cents. The results showed that 6 or 70 Hz HD-tACS over the left IFG led to larger magnitudes and longer latencies of vocal compensations for pitch perturbations paralleled by larger ERP P2 responses than sham HD-tACS. Moreover, there was a lack of frequency specificity that showed no significant differences between 6 and 70 Hz HD-tACS. These findings provide first causal evidence linking the left IFG to vocal pitch regulation, suggesting that the left IFG is an important part of the feedback control network that mediates vocal compensations for auditory feedback errors.

Continuous theta-burst stimulation over the left posterior inferior frontal gyrus induced compensatory plasticity in the language network

Introduction

Continuous theta-burst stimulation (cTBS) has been used as an effective tool in inducing inhibitory aftereffect within a short time periods in the motor cortex; this has been demonstrated in the language network to a limited degree with controversial effect. In this study, we aimed to delineate the offline effect of cTBS-induced changes to the left posterior inferior frontal gyrus (pIFG) in healthy subjects using functional magnetic resonance imaging (fMRI).

Methods

Twenty healthy, normal subjects (mean age: 30.84 years) were recruited. They all were right-handed and had no contra-indications for fMRI or cTBS. They were randomly assigned into the treatment group or the sham control group.

Results

ANOVA showed that cTBS had a significant main effect only when the sham treatment was subtracted from the real stimulation in left superior temporal, left inferior frontal gyrus, thalamus, and right insular cortex (uncorrected p < 0.002). The subjects' post-cTBS condition differed significantly from their pre-cTBS condition in the left pIFG (uncorrected p < 0.002). There were interactions in the pIFG, bilateral superior parietal lobules, left superior temporal, left supramarginal, and left cuneus areas. The application of cTBS induced increased BOLD signals in language-related networks by stimulating the left pIFG (BA 44). This implies that inhibiting the pIFG led to increased use of language network resources.

Conclusion

This study demonstrated cTBS-induced changes in the language network caused by stimulation of the left pIFG. Based on these findings, future studies on the therapeutic effects of cTBS on the right Broca's homolog area are warranted.

A systematic review and meta-analysis of the efficacy of intermittent theta burst stimulation (iTBS) on cognitive enhancement

Intermittent theta-burst stimulation (iTBS) has been used to focally regulate excitability of neural cortex over the past decade - however there is little consensus on the generalizability of effects reported in individual studies. Many studies use small sample sizes (N < 30), and there is a considerable amount of methodological heterogeneity in application of the stimulation itself. This systematic meta-analysis aims to consolidate the extant literature and determine if up-regulatory theta-burst stimulation reliably enhances cognition through measurable behavior. Results show that iTBS - when compared to suitable control conditions - may enhance cognition when outlier studies are removed, but also that there is a significant amount of heterogeneity across studies. Significant contributors to between-study heterogeneity include location of stimulation and method of navigation to the stimulation site. Surprisingly, the type of cognitive domain investigated was not a significant contributor of heterogeneity. The findings of this meta-analysis demonstrate that standardization of iTBS is urgent and necessary to determine if neuroenhancement of particular cognitive faculties are reliable and robust, and measurable through observable behavior.

Faces and Voices Processing in Human and Primate Brains: Rhythmic and Multimodal Mechanisms Underlying the Evolution and Development of Speech

While influential works since the 1970s have widely assumed that imitation is an innate skill in both human and non-human primate neonates, recent empirical studies and meta-analyses have challenged this view, indicating other forms of reward-based learning as relevant factors in the development of social behavior. The visual input translation into matching motor output that underlies imitation abilities instead seems to develop along with social interactions and sensorimotor experience during infancy and childhood. Recently, a new visual stream has been identified in both human and non-human primate brains, updating the dual visual stream model. This third pathway is thought to be specialized for dynamics aspects of social perceptions such as eye-gaze, facial expression and crucially for audio-visual integration of speech. Here, we review empirical studies addressing an understudied but crucial aspect of speech and communication, namely the processing of visual orofacial cues (i.e., the perception of a speaker's lips and tongue movements) and its integration with vocal auditory cues. Along this review, we offer new insights from our understanding of speech as the product of evolution and development of a rhythmic and multimodal organization of sensorimotor brain networks, supporting volitional motor control of the upper vocal tract and audio-visual voices-faces integration.

A comparison and classification of oscillatory characteristics in speech perception and covert speech

Covert speech, the mental imagery of speaking, has been studied increasingly to understand and decode thoughts in the context of brain-computer interfaces. In studies of speech comprehension, neural oscillations are thought to play a key role in the temporal encoding of speech. However, little is known about the role of oscillations in covert speech. In this study, we investigated the oscillatory involvements in covert speech and speech perception. Data were collected from 10 participants with 64 channel EEG. Participants heard the words, 'blue' and 'orange', and subsequently mentally rehearsed them. First, continuous wavelet transform was performed on epoched signals and subsequently two-tailed t-tests between two classes were conducted to determine statistical differences in frequency and time (t-CWT). Features were also extracted using t-CWT and subsequently classified using a support vector machine. θ and γ phase amplitude coupling (PAC) was also assessed within and between tasks. All binary classifications produced accuracies significantly greater (80-90%) than chance level, supporting the use of t-CWT in determining relative oscillatory involvements. While the perception task dynamically invoked all frequencies with more prominent θ and α activity, the covert task favoured higher frequencies with significantly higher γ activity than perception. Moreover, the perception condition produced significant θ-γ PAC, corroborating a reported linkage between syllabic and phonemic sampling. Although this coupling was found to be suppressed in the covert condition, we found significant cross-task coupling between perception θ and covert speech γ. Covert speech processing appears to be largely associated with higher frequencies of EEG. Importantly, the significant cross-task coupling between speech perception and covert speech, in the absence of within-task covert speech PAC, supports the notion that the γ- and θ-bands subserve, respectively, shared and unique encoding processes across tasks.

The effects of continuous oromotor activity on speech motor learning: speech biomechanics and neurophysiologic correlates

Sustained limb motor activity has been used as a therapeutic tool for improving rehabilitation outcomes and is thought to be mediated by neuroplastic changes associated with activity-induced cortical excitability. Although prior research has reported enhancing effects of continuous chewing and swallowing activity on learning, the potential beneficial effects of sustained oromotor activity on speech improvements is not well-documented. This exploratory study was designed to examine the effects of continuous oromotor activity on subsequent speech learning. Twenty neurologically healthy young adults engaged in periods of continuous chewing and speech after which they completed a novel speech motor learning task. The motor learning task was designed to elicit improvements in accuracy and efficiency of speech performance across repetitions of eight-syllable nonwords. In addition, transcranial magnetic stimulation was used to measure the cortical silent period (cSP) of the lip motor cortex before and after the periods of continuous oromotor behaviors. All repetitions of the nonword task were recorded acoustically and kinematically using a three-dimensional motion capture system. Productions were analyzed for accuracy and duration, as well as lip movement distance and speed. A control condition estimated baseline improvement rates in speech performance. Results revealed improved speech performance following 10 min of chewing. In contrast, speech performance following 10 min of continuous speech was degraded. There was no change in the cSP as a result of either oromotor activity. The clinical implications of these findings are discussed in the context of speech rehabilitation and neuromodulation.

Improving speech perception in noise in young and older adults using transcranial magnetic stimulation

Normal aging is associated with speech perception in noise (SPiN) difficulties. The objective of this study was to determine if SPiN performance can be enhanced by intermittent theta-burst stimulation (iTBS) in young and older adults.

METHOD

We developed a sub-lexical SPiN test to evaluate the contribution of age, hearing, and cognition to SPiN performance in young and older adults. iTBS was applied to the left posterior superior temporal sulcus (pSTS) and the left ventral premotor cortex (PMv) to examine its impact on SPiN performance.

RESULTS

Aging was associated with reduced SPiN accuracy. TMS-induced performance gain was greater after stimulation of the PMv compared to the pSTS. Participants with lower scores in the baseline condition improved the most.

DISCUSSION

SPiN difficulties can be reduced by enhancing activity within the left speech-processing network in adults. This study paves the way for the development of TMS-based interventions to reduce SPiN difficulties in adults.

What Happened to Mirror Neurons?

Ten years ago, Perspectives in Psychological Science published the Mirror Neuron Forum, in which authors debated the role of mirror neurons in action understanding, speech, imitation, and autism and asked whether mirror neurons are acquired through visual-motor learning. Subsequent research on these themes has made significant advances, which should encourage further, more systematic research. For action understanding, multivoxel pattern analysis, patient studies, and brain stimulation suggest that mirror-neuron brain areas contribute to low-level processing of observed actions (e.g., distinguishing types of grip) but not to high-level action interpretation (e.g., inferring actors’ intentions). In the area of speech perception, although it remains unclear whether mirror neurons play a specific, causal role in speech perception, there is compelling evidence for the involvement of the motor system in the discrimination of speech in perceptually noisy conditions. For imitation, there is strong evidence from patient, brain-stimulation, and brain-imaging studies that mirror-neuron brain areas play a causal role in copying of body movement topography. In the area of autism, studies using behavioral and neurological measures have tried and failed to find evidence supporting the “broken-mirror theory” of autism. Furthermore, research on the origin of mirror neurons has confirmed the importance of domain-general visual-motor associative learning rather than canalized visual-motor learning, or motor learning alone.

Case Report: Barely Able to Speak, Can't Stop Echoing: Echolalic Dynamic Aphasia in Progressive Supranuclear Palsy

The diagnostic criteria for progressive supranuclear palsy (PSP) incorporate two speech-language disturbances (SLDs), non-fluent/agrammatic primary progressive aphasia and progressive apraxia of speech, but overlook the inclusion of other SLDs, including dynamic aphasia (DA). Thus, there is a need to reappraise the broad spectrum of SLDs in PSP to include other presenting phenotypes. Here we report findings from the study of two elderly patients with PSP presenting with DA and irrepressible echolalia. Both patients had markedly impoverished verbal production, but their performance in other tasks (repetition and naming) and auditory comprehension were preserved or only mildly impaired. Experimental tests of DA revealed impaired word and sentence generation in response to verbal and non-verbal stimuli. Additional language and cognitive testing revealed different types of echolalia (mitigated, automatic, and echoing approval) as well as impaired inhibitory control and social cognition (mentalizing). Both patients had negative neuropsychiatric alterations (i.e., apathy, aspontaneity, and indifference/emotional flatness). Brain magnetic resonance imaging in both patients showed atrophy of the midbrain tegmentum and superior medial frontal cortex suggestive of PSP, yet further evaluation of the neural correlates using multimodal neuroimaging and neuropathological data was not performed. However, based on the already known neural basis of DA and echolalia in PSP and stroke, we suggest that, in the present cases, neurodegeneration in the midbrain tegmentum, superior medial frontal lobe, and caudate nucleus was responsible for DA and that decreased activity in these regions may play a permissive role for eliciting verbal echoing via disinhibition of the perisylvian speech-language network.

Probing rapid network reorganization of motor and language functions via neuromodulation and neuroimaging

Motor and cognitive functions are organized in large-scale networks in the human brain that interact to enable flexible adaptation of information exchange to ever-changing environmental conditions. In this review, we discuss the unique potential of the consecutive combination of repetitive transcranial magnetic stimulation (rTMS) and functional neuroimaging to probe network organization and reorganization in the healthy and lesioned brain. First, we summarize findings highlighting the flexible (re-)distribution and short-term reorganization in motor and cognitive networks in the healthy brain. Plastic after-effects of rTMS result in large-scale changes on the network level affecting both local and remote activity within the stimulated network as well as interactions between the stimulated and distinct functional networks. While the number of combined rTMS-fMRI studies in patients with brain lesions remains scarce, preliminary evidence suggests that the lesioned brain flexibly (re-)distributes its computational capacities to functionally reorganize impaired brain functions, using a similar set of mechanisms to achieve adaptive network plasticity compared to short-term reorganization observed in the healthy brain after rTMS. In general, both short-term reorganization in the healthy brain and stroke-induced reorganization seem to rely on three general mechanisms of adaptive network plasticity that allow to maintain and recover function: i) interhemispheric changes, including increased contribution of homologous regions in the contralateral hemisphere and increased interhemispheric connectivity, ii) increased interactions between differentially specialized networks and iii) increased contributions of domain-general networks after disruption of more specific functions. These mechanisms may allow for computational flexibility of large-scale neural networks underlying motor and cognitive functions. Future studies should use complementary approaches to address the functional relevance of adaptive network plasticity and further delineate how these general mechanisms interact to enable network flexibility. Besides furthering our neurophysiological insights into brain network interactions, identifying approaches to support and enhance adaptive network plasticity may result in clinically relevant diagnostic and treatment approaches.

Top–Down Inhibitory Mechanisms Underlying Auditory–Motor Integration for Voice Control: Evidence by TMS

The dorsolateral prefrontal cortex (DLPFC) has been implicated in auditory–motor integration for accurate control of vocal production, but its precise role in this feedback-based process remains largely unknown. To this end, the present event-related potential study applied a transcranial magnetic stimulation (TMS) protocol, continuous theta-burst stimulation (c-TBS), to disrupt cortical activity in the left DLPFC as young adults vocalized vowel sounds while hearing their voice unexpectedly shifted upwards in pitch. The results showed that, as compared to the sham condition, c-TBS over left DLPFC led to significantly larger vocal compensations for pitch perturbations that were accompanied by significantly smaller cortical P2 responses. Source localization analyses revealed that this brain activity pattern was the result of reduced activation in the left superior frontal gyrus and right inferior parietal lobule (supramarginal gyrus). These findings demonstrate c-TBS-induced modulatory effects of DLPFC on the neurobehavioral processing of vocal pitch regulation, suggesting that disrupting prefrontal function may impair top–down inhibitory control mechanisms that prevent speech production from being excessively influenced by auditory feedback, resulting in enhanced vocal compensations for feedback perturbations. This is the first study that provides direct evidence for a causal role of the left DLPFC in auditory feedback control of vocal production.

Neural Patterns in Linguistic Cortices Discriminate the Content of Verbal Working Memory

An influential theoretical account of working memory (WM) considers that WM is based on direct activation of long-term memory knowledge. While there is empirical support for this position in the visual WM domain, direct evidence is scarce in the verbal WM domain. This question is critical for models of verbal WM, as the question of whether short-term maintenance of verbal information relies on direct activation within the long-term linguistic knowledge base or not is still debated. In this study, we examined the extent to which short-term maintenance of lexico-semantic knowledge relies on neural activation patterns in linguistic cortices, and this by using a fast encoding running span task for word and nonword stimuli minimizing strategic encoding mechanisms. Multivariate analyses showed specific neural patterns for the encoding and maintenance of word versus nonword stimuli. These patterns were not detectable anymore when participants were instructed to stop maintaining the memoranda. The patterns involved specific regions within the dorsal and ventral pathways, which are considered to support phonological and semantic processing to various degrees. This study provides novel evidence for a role of linguistic cortices in the representation of long-term memory linguistic knowledge during WM processing.

Repetitive verbal behaviors are not always harmful signs: Compensatory plasticity within the language network in aphasia

Repetitive verbal behaviors such as conduite d'approche (CdA) and mitigated echolalia (ME) are well-known phenomena since early descriptions of aphasia. Nevertheless, there is no substantial fresh knowledge on their clinical features, neural correlates and treatment interventions. In the present study we take advantage of three index cases of chronic fluent aphasia showing CdA, ME or both symptoms to dissect their clinical and neural signatures. Using multimodal neuroimaging (structural magnetic resonance imaging and [18]-fluorodeoxyglucose positron emission tomography during resting state), we found that despite of the heterogeneous lesions in terms of etiology (stroke, traumatic brain injury), volume and location, CdA was present when the lesion affected in greater extent the left dorsal language pathway, while ME resulted from preferential damage to the left ventral stream. The coexistence of CdA and ME was associated with involvement of areas overlapping with the structural lesions and metabolic derangements described in the subjects who showed one of these symptoms (CdA or ME). These findings suggest that CdA and ME represent the clinical expression of plastic changes that occur within the spared language network and its interconnected areas in order to compensate for the linguistic functions that previously relied on the activity of the damaged pathway. We discuss the results in the light of this idea and consider alternative undamaged neural networks that may support CdA and ME.

Reduced Performance During a Sentence Repetition Task by Continuous Theta-Burst Magnetic Stimulation of the Pre-supplementary Motor Area

The pre-supplementary motor area (pre-SMA) is engaged in speech comprehension under difficult circumstances such as poor acoustic signal quality or time-critical conditions. Previous studies found that left pre-SMA is activated when subjects listen to accelerated speech. Here, the functional role of pre-SMA was tested for accelerated speech comprehension by inducing a transient “virtual lesion” using continuous theta-burst stimulation (cTBS). Participants were tested (1) prior to (pre-baseline), (2) 10 min after (test condition for the cTBS effect), and (3) 60 min after stimulation (post-baseline) using a sentence repetition task (formant-synthesized at rates of 8, 10, 12, 14, and 16 syllables/s). Speech comprehension was quantified by the percentage of correctly reproduced speech material. For high speech rates, subjects showed decreased performance after cTBS of pre-SMA. Regarding the error pattern, the number of incorrect words without any semantic or phonological similarity to the target context increased, while related words decreased. Thus, the transient impairment of pre-SMA seems to affect its inhibitory function that normally eliminates erroneous speech material prior to speaking or, in case of perception, prior to encoding into a semantically/pragmatically meaningful message.

Cholinergic Potentiation and Audiovisual Repetition-Imitation Therapy Improve Speech Production and Communication Deficits in a Person with Crossed Aphasia by Inducing Structural Plasticity in White Matter Tracts

Donepezil (DP), a cognitive-enhancing drug targeting the cholinergic system, combined with massed sentence repetition training augmented and speeded up recovery of speech production deficits in patients with chronic conduction aphasia and extensive left hemisphere infarctions (Berthier et al., 2014). Nevertheless, a still unsettled question is whether such improvements correlate with restorative structural changes in gray matter and white matter pathways mediating speech production. In the present study, we used pharmacological magnetic resonance imaging to study treatment-induced brain changes in gray matter and white matter tracts in a right-handed male with chronic conduction aphasia and a right subcortical lesion (crossed aphasia). A single-patient, open-label multiple-baseline design incorporating two different treatments and two post-treatment evaluations was used. The patient received an initial dose of DP (5 mg/day) which was maintained during 4 weeks and then titrated up to 10 mg/day and administered alone (without aphasia therapy) during 8 weeks (Endpoint 1). Thereafter, the drug was combined with an audiovisual repetition-imitation therapy (Look-Listen-Repeat, LLR) during 3 months (Endpoint 2). Language evaluations, diffusion weighted imaging (DWI), and voxel-based morphometry (VBM) were performed at baseline and at both endpoints in JAM and once in 21 healthy control males. Treatment with DP alone and combined with LLR therapy induced marked improvement in aphasia and communication deficits as well as in selected measures of connected speech production, and phrase repetition. The obtained gains in speech production remained well-above baseline scores even 4 months after ending combined therapy. Longitudinal DWI showed structural plasticity in the right frontal aslant tract and direct segment of the arcuate fasciculus with both interventions. VBM revealed no structural changes in other white matter tracts nor in cortical areas linked by these tracts. In conclusion, cholinergic potentiation alone and combined with a model-based aphasia therapy improved language deficits by promoting structural plastic changes in right white matter tracts.

Adaptive Plasticity in the Healthy Language Network: Implications for Language Recovery after Stroke

Across the last three decades, the application of noninvasive brain stimulation (NIBS) has substantially increased the current knowledge of the brain's potential to undergo rapid short-term reorganization on the systems level. A large number of studies applied transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) in the healthy brain to probe the functional relevance and interaction of specific areas for different cognitive processes. NIBS is also increasingly being used to induce adaptive plasticity in motor and cognitive networks and shape cognitive functions. Recently, NIBS has been combined with electrophysiological techniques to modulate neural oscillations of specific cortical networks. In this review, we will discuss recent advances in the use of NIBS to modulate neural activity and effective connectivity in the healthy language network, with a special focus on the combination of NIBS and neuroimaging or electrophysiological approaches. Moreover, we outline how these results can be transferred to the lesioned brain to unravel the dynamics of reorganization processes in poststroke aphasia. We conclude with a critical discussion on the potential of NIBS to facilitate language recovery after stroke and propose a phase-specific model for the application of NIBS in language rehabilitation.

Non-invasive brain stimulation of the aging brain: State of the art and future perspectives

Favored by increased life expectancy and reduced birth rate, worldwide demography is rapidly shifting to older ages. The golden age of aging is not only an achievement but also a big challenge because of the load of the elderly on social and medical health care systems. Moreover, the impact of age-related decline of attention, memory, reasoning and executive functions on self-sufficiency emphasizes the need of interventions to maintain cognitive abilities at a useful degree in old age. Recently, neuroscientific research explored the chance to apply Non-Invasive Brain Stimulation (NiBS) techniques (as transcranial electrical and magnetic stimulation) to healthy aging population to preserve or enhance physiologically-declining cognitive functions. The present review will update and address the current state of the art on NiBS in healthy aging. Feasibility of NiBS techniques will be discussed in light of recent neuroimaging (either structural or functional) and neurophysiological models proposed to explain neural substrates of the physiologically aging brain. Further, the chance to design multidisciplinary interventions to maximize the efficacy of NiBS techniques will be introduced as a necessary future direction.

Neurobiological Correlates of Inhibition of the Right Broca Homolog during New-Word Learning

Repetitive transcranial magnetic stimulation (rTMS) has demonstrated beneficial effects on motor learning. It would be important to obtain a similar enhancement for verbal learning. However, previous studies have mostly assessed short-term effects of rTMS on language performance and the effect on learning is largely unknown. This study examined whether an inhibition of the right Broca homolog has long-term impact on neural processes underlying the acquisition of new words in healthy individuals. Sixteen young participants trained a new-word learning paradigm with rare, mostly unknown objects and their corresponding words immediately after continuous theta burst stimulation (cTBS) or sham stimulation of right inferior frontal gyrus (IFG) in a cross-over design. Neural effects were assessed with electroencephalography (EEG) source power analyses during the naming task as well as coherence analyses at rest 1 day before and after training. Inhibition of the right Broca homolog did not affect new word learning performance at the group level. Behavioral and neural responses to cTBS were variable across participants and were associated with the magnitude of resting-state alpha-band coherence between the stimulated area and the rest of the brain before stimulation. Only participants with high intrinsic alpha-band coherence between the stimulated area and the rest of the brain before stimulation showed the expected inhibition during naming and greater learning performance. In conclusion, our study confirms that cTBS can induce lasting modulations of neural processes which are associated with learning, but the effect depends on the individual network state.

The role of the supplementary motor area for speech and language processing

Apart from its function in speech motor control, the supplementary motor area (SMA) has largely been neglected in models of speech and language processing in the brain. The aim of this review paper is to summarize more recent work, suggesting that the SMA has various superordinate control functions during speech communication and language reception, which is particularly relevant in case of increased task demands. The SMA is subdivided into a posterior region serving predominantly motor-related functions (SMA proper) whereas the anterior part (pre-SMA) is involved in higher-order cognitive control mechanisms. In analogy to motor triggering functions of the SMA proper, the pre-SMA seems to manage procedural aspects of cognitive processing. These latter functions, among others, comprise attentional switching, ambiguity resolution, context integration, and coordination between procedural and declarative memory structures. Regarding language processing, this refers, for example, to the use of inner speech mechanisms during language encoding, but also to lexical disambiguation, syntax and prosody integration, and context-tracking.

Left dorsal speech stream components and their contribution to phonological processing

Models propose an auditory-motor mapping via a left-hemispheric dorsal speech-processing stream, yet its detailed contributions to speech perception and production are unclear. Using fMRI-navigated repetitive transcranial magnetic stimulation (rTMS), we virtually lesioned left dorsal stream components in healthy human subjects and probed the consequences on speech-related facilitation of articulatory motor cortex (M1) excitability, as indexed by increases in motor-evoked potential (MEP) amplitude of a lip muscle, and on speech processing performance in phonological tests. Speech-related MEP facilitation was disrupted by rTMS of the posterior superior temporal sulcus (pSTS), the sylvian parieto-temporal region (SPT), and by double-knock-out but not individual lesioning of pars opercularis of the inferior frontal gyrus (pIFG) and the dorsal premotor cortex (dPMC), and not by rTMS of the ventral speech-processing stream or an occipital control site. RTMS of the dorsal stream but not of the ventral stream or the occipital control site caused deficits specifically in the processing of fast transients of the acoustic speech signal. Performance of syllable and pseudoword repetition correlated with speech-related MEP facilitation, and this relation was abolished with rTMS of pSTS, SPT, and pIFG. Findings provide direct evidence that auditory-motor mapping in the left dorsal stream causes reliable and specific speech-related MEP facilitation in left articulatory M1. The left dorsal stream targets the articulatory M1 through pSTS and SPT constituting essential posterior input regions and parallel via frontal pathways through pIFG and dPMC. Finally, engagement of the left dorsal stream is necessary for processing of fast transients in the auditory signal.

Audiological findings in aphasic patients after stroke

Objective

To outline the audiological findings of aphasic patients after cerebrovascular accidents.

Methods

This is a cross-sectional study performed between March 2011 and August 2012 in the Speech, Language, and Hearing Pathology Department of the Universidade Federal de São Paulo. A total of 43 aphasic subjects (27 men) were referred for audiological evaluation after stroke, with mean age of 54.48 years. Basic audiological evaluation tests were performed, including pure tone audiometry, speech audiometry (speech recognition threshold and word recognition score), immittance measures (tympanometry and contralateral acoustic reflex), and transient otoacoustic emissions.

Results

Sensorineural hearing loss was prevalent (78.6%). Speech recognition threshold and word recognition score were not obtained in some patients because they were unable to perform the task. Hearing loss was a common finding in this population.

Conclusion

Comprehension and/or oral emission disruptions in aphasic patients after stroke compromised conventional speech audiometry, resulting in the need for changes in the evaluation procedures for these patients.

Does rTMS alter neurocognitive functioning in patients with panic disorder/agoraphobia? An fNIRS-based investigation of prefrontal activation during a cognitive task and its modulation via sham-controlled rTMS

OBJECTIVES

Neurobiologically, panic disorder (PD) is supposed to be characterised by cerebral hypofrontality. Via functional near-infrared spectroscopy (fNIRS), we investigated whether prefrontal hypoactivity during cognitive tasks in PD-patients compared to healthy controls (HC) could be replicated. As intermittent theta burst stimulation (iTBS) modulates cortical activity, we furthermore investigated its ability to normalise prefrontal activation.

METHODS

Forty-four PD-patients, randomised to sham or verum group, received 15 iTBS-sessions above the left dorsolateral prefrontal cortex (DLPFC) in addition to psychoeducation. Before first and after last iTBS-treatment, cortical activity during a verbal fluency task was assessed via fNIRS and compared to the results of 23 HC.

RESULTS

At baseline, PD-patients showed hypofrontality including the DLPFC, which differed significantly from activation patterns of HC. However, verum iTBS did not augment prefrontal fNIRS activation. Solely after sham iTBS, a significant increase of measured fNIRS activation in the left inferior frontal gyrus (IFG) during the phonological task was found.

CONCLUSION

Our results support findings that PD is characterised by prefrontal hypoactivation during cognitive performance. However, verum iTBS as an "add-on" to psychoeducation did not augment prefrontal activity. Instead we only found increased fNIRS activation in the left IFG after sham iTBS application. Possible reasons including task-related psychophysiological arousal are discussed.

Treatment of major depression with bilateral theta burst stimulation: a randomized controlled pilot trial

BACKGROUND

Current efforts to improve clinical effectiveness and utility of repetitive transcranial magnetic stimulation (rTMS) in the treatment of major depression (MD) include theta burst stimulation (TBS), a patterned form of rTMS. Here, we investigated the efficacy of bilateral TBS to the dorsolateral prefrontal cortex (dlPFC) in patients with MD in additon to ongoing medication and psychotherapy.

METHODS

In this randomized-controlled trial, thirty-two patients with MD were treated for six weeks (thirty sessions) with either successively intermittent, activity enhancing TBS (iTBS) to the left and continuous, inhibiting TBS (cTBS) to the right dlPFC or with bilateral sham stimulation. Primary outcome measure was the proportion of treatment response defined as a Montgomery-Åsberg Depression Rating Scale (MADRS)≤50% compared to baseline. Secondary outcomes comprised response and remission rates of the Hamilton Depression Rating Scale (HAMD) and the Beck Depression Inventory (BDI).

RESULTS

A larger number of responders were found in the cTBS (n=9) compared to the sham-stimulation (n=4) group (odds ratio: 3.86; Wald χ(2)=3.9, p=0.048). On secondary endpoint analysis, patient-reported outcome as assessed by the BDI, pointed towards a higher rate of remitters in the cTBS (n=6) than in the sham (n=1) group (odds ratio: 9; Wald χ(2)=3.5, p=0.061).

LIMITATIONS

With regard to the pilot character of the study and the small sample size, the results have to be considered as preliminary.

CONCLUSIONS

These findings provide first evidence that six weeks treatment of MDD with iTBS to the left and cTBS to the right dlPFC for six weeks is safe, feasible and superior to sham stimulation applied add-on to pharmacological and psychotherapeutic treatment.

Task-dependent activity and connectivity predict episodic memory network-based responses to brain stimulation in healthy aging

BACKGROUND

Transcranial magnetic stimulation (TMS) can affect episodic memory, one of the main cognitive hallmarks of aging, but the mechanisms of action remain unclear.

OBJECTIVES

To evaluate the behavioral and functional impact of excitatory TMS in a group of healthy elders.

METHODS

We applied a paradigm of repetitive TMS - intermittent theta-burst stimulation - over left inferior frontal gyrus in healthy elders (n = 24) and evaluated its impact on the performance of an episodic memory task with two levels of processing and the associated brain activity as captured by a pre and post fMRI scans.

RESULTS

In the post-TMS fMRI we found TMS-related activity increases in left prefrontal and cerebellum-occipital areas specifically during deep encoding but not during shallow encoding or at rest. Furthermore, we found a task-dependent change in connectivity during the encoding task between cerebellum-occipital areas and the TMS-targeted left inferior frontal region. This connectivity change correlated with the TMS effects over brain networks.

CONCLUSIONS

The results suggest that the aged brain responds to brain stimulation in a state-dependent manner as engaged by different tasks components and that TMS effect is related to inter-individual connectivity changes measures. These findings reveal fundamental insights into brain network dynamics in aging and the capacity to probe them with combined behavioral and stimulation approaches.

Utility of TMS to understand the neurobiology of speech

According to a traditional view, speech perception and production are processed largely separately in sensory and motor brain areas. Recent psycholinguistic and neuroimaging studies provide novel evidence that the sensory and motor systems dynamically interact in speech processing, by demonstrating that speech perception and imitation share regional brain activations. However, the exact nature and mechanisms of these sensorimotor interactions are not completely understood yet. Transcranial magnetic stimulation (TMS) has often been used in the cognitive neurosciences, including speech research, as a complementary technique to behavioral and neuroimaging studies. Here we provide an up-to-date review focusing on TMS studies that explored speech perception and imitation. Single-pulse TMS of the primary motor cortex (M1) demonstrated a speech specific and somatotopically specific increase of excitability of the M1 lip area during speech perception (listening to speech or lip reading). A paired-coil TMS approach showed increases in effective connectivity from brain regions that are involved in speech processing to the M1 lip area when listening to speech. TMS in virtual lesion mode applied to speech processing areas modulated performance of phonological recognition and imitation of perceived speech. In summary, TMS is an innovative tool to investigate processing of speech perception and imitation. TMS studies have provided strong evidence that the sensory system is critically involved in mapping sensory input onto motor output and that the motor system plays an important role in speech perception.