Individual differences in premotor and motor recruitment during speech perception

Although activity in premotor and motor cortices is commonly observed in neuroimaging studies of spoken language processing, the degree to which this activity is an obligatory part of everyday speech comprehension remains unclear. We hypothesised that rather than being a unitary phenomenon, the neural response to speech perception in motor regions would differ across listeners as a function of individual cognitive ability. To examine this possibility, we used functional magnetic resonance imaging (fMRI) to investigate the neural processes supporting speech perception by comparing active listening to pseudowords with matched tasks that involved reading aloud or repetition, all compared to acoustically matched control stimuli and matched baseline tasks. At a whole-brain level there was no evidence for recruitment of regions in premotor or motor cortex during speech perception. A focused region of interest analysis similarly failed to identify significant effects, although a subset of regions approached significance, with notable variability across participants. We then used performance on a battery of behavioural tests that assessed meta-phonological and verbal short-term memory abilities to investigate the reasons for this variability, and found that individual differences in particular in low phonotactic probability pseudoword repetition predicted participants' neural activation within regions in premotor and motor cortices during speech perception. We conclude that normal listeners vary in the degree to which they recruit premotor and motor cortex as a function of short-term memory ability. This is consistent with a resource-allocation approach in which recruitment of the dorsal speech processing pathway depends on both individual abilities and specific task demands.     

Foreign accent syndrome: Behavioural and anatomical findings in recovered and non-recovered patients

Abstract

Four right-handed monolingual Spanish-speaking patients who developed a foreign accent syndrome (FAS) during the recovery period from a non-fluent aphasia or an aphemia are reported. The FAS resolved rapidly (within 2 months) in two patients, both with small stroke lesions in the posterior margin of the left middle frontal gyrus. In the other two patients, who had lesions involving the middle portion of the left precentral gyrus and the white matter underlying the right sensory-motor cortex, the FAS lasted more than 1 year. Phonetic and fundamental frequency (F0) analysis showed atypical articulatory and prosodic patterns in the two patients with a long-lasting FAS, but only abnormal prosodic features in the two recovered cases. These findings suggest that: (1) a selective involvement of specific portions of Brodmann's areas 4 and 6, and/or its subcortical projections, may account for the peculiar combination of segmental and prosodic deficits underlying the FAS; and (2) recovery seems to be related to small variations in lesion location, since a transient FAS was associated with damage to cortical areas implicated in the modulation of speech prosody (i.e. premotor cortex), while a longer-lasting FAS was associated with damage restricted to areas mainly related to articulation (i.e. precentral gyrus).     

Discriminating between auditory and motor cortical responses to speech and nonspeech mouth sounds

Several perspectives on speech perception posit a central role for the representation of articulations in speech comprehension, supported by evidence for premotor activation when participants listen to speech. However, no experiments have directly tested whether motor responses mirror the profile of selective auditory cortical responses to native speech sounds or whether motor and auditory areas respond in different ways to sounds. We used fMRI to investigate cortical responses to speech and nonspeech mouth (ingressive click) sounds. Speech sounds activated bilateral superior temporal gyri more than other sounds, a profile not seen in motor and premotor cortices. These results suggest that there are qualitative differences in the ways that temporal and motor areas are activated by speech and click sounds: Anterior temporal lobe areas are sensitive to the acoustic or phonetic properties, whereas motor responses may show more generalized responses to the acoustic stimuli.     

Immediate and long‐term effects of speech treatment targets and intensive dosage on Parkinson's disease dysphonia and the speech motor network: Randomized controlled trial

This study compared acoustic and neural changes accompanying two treatments matched for intensive dosage but having two different treatment targets (voice or articulation) to dissociate the effects of treatment target and intensive dosage in speech therapies. Nineteen participants with Parkinsonian dysphonia (11 F) were randomized to three groups: intensive treatment targeting voice (voice group, n = 6), targeting articulation (articulation group, n = 7), or an untreated group (no treatment, n = 6). The severity of dysphonia was assessed by the smoothed cepstral peak prominence (CPPS) and neuronal changes were evaluated by cerebral blood flow (CBF) recorded at baseline, posttreatment, and 7‐month follow‐up. Only the voice treatment resulted in significant posttreatment improvement in CPPS, which was maintained at 7 months. Following voice treatment, increased activity in left premotor and bilateral auditory cortices was observed at posttreatment, and in the left motor and auditory cortices at 7‐month follow‐up. Articulation treatment resulted in increased activity in bilateral premotor and left insular cortices that were sustained at a 7‐month follow‐up. Activation in the auditory cortices and a significant correlation between the CPPS and CBF in motor and auditory cortices was observed only in the voice group. The intensive dosage resulted in long‐lasting behavioral and neural effects as the no‐treatment group showed a progressive decrease in activity in areas of the speech motor network out to a 7‐month follow‐up. These results indicate that dysphonia and the speech motor network can be differentially modified by treatment targets, while intensive dosage contributes to long‐lasting effects of speech treatments.     

Brain damage and cortical compensation in foreign accent syndrome

Foreign Accent Syndrome (FAS) is a well-known neurological deficit whose underlying cause has remained obscure despite almost a century of study. Combining structural and functional imaging, our studies suggest that FAS represents a compensatory response to impaired motor regulation of speech. We describe a patient who acquired FAS as a result of an ischemic stroke in the left basal ganglia. In addition to this case being exceptionally clean, we were able to confirm a specific lesion location as well as provide strong evidence that impaired motor speech regulation resulted in compensation by other areas of the cortical motor speech network.     

Brain damage and cortical compensation in foreign accent syndrome

Foreign Accent Syndrome (FAS) is a well-known neurological deficit whose underlying cause has remained obscure despite almost a century of study. Combining structural and functional imaging, our studies suggest that FAS represents a compensatory response to impaired motor regulation of speech. We describe a patient who acquired FAS as a result of an ischemic stroke in the left basal ganglia. In addition to this case being exceptionally clean, we were able to confirm a specific lesion location as well as provide strong evidence that impaired motor speech regulation resulted in compensation by other areas of the cortical motor speech network.     

Foreign accent syndrome as a developmental motor speech disorder

Introduction

Foreign Accent Syndrome (FAS) is a relatively rare motor speech disorder in which the pronunciation of a patient is perceived by listeners of the same language community as distinctly foreign. FAS has been well documented in adult patients with etiologically heterogeneous, though mostly vascular brain lesions affecting the motor speech network of the language dominant hemisphere. In addition, reports exist of adult patients in whom FAS was due to a psychiatric illness. Although FAS has been reported in children, such accounts are rare and have remained largely anecdotal in that there have been no formally documented cases of FAS as a developmental motor speech disorder.

Methods and results

For the first time, we describe the clinical, cognitive and neurolinguistic findings in two patients who in the absence of a history of psychiatric illness or acquired brain damage already presented with FAS at an early stage of speech and language development. In the first patient “developmental FAS” was associated with a dysharmonic distribution of neurocognitive test results indicating slight underdevelopment of visuo-spatial skills and visual memory. The second patient presented with “developmental FAS” associated with specific language impairment (SLI). Independent support for a diagnosis of FAS in both patients was obtained in an accent attribution experiment in which groups of native speakers of (Belgian) Dutch assessed the type of foreign accent of a sample of the patients’ conversational speech. Both patients were judged as non-native speakers of Dutch by the majority of participants who predominantly identified the accent as French.

Conclusion

This paper for the first time documents two patients who presented with FAS on a developmental basis. The finding that FAS does not only occur in the context of acquired brain damage or psychogenic illness but also exists as developmental motor speech impairment requires a re-definition of FAS as a clinical syndrome.     

Functional MRI assessment of orofacial articulators: neural correlates of lip, jaw, larynx, and tongue movements

Compared with complex coordinated orofacial actions, few neuroimaging studies have attempted to determine the shared and distinct neural substrates of supralaryngeal and laryngeal articulatory movements when performed independently. To determine cortical and subcortical regions associated with supralaryngeal motor control, participants produced lip, tongue and jaw movements while undergoing functional magnetic resonance imaging (fMRI). For laryngeal motor activity, participants produced the steady-state/i/vowel. A sparse temporal sampling acquisition method was used to minimize movement-related artifacts. Three main findings were observed. First, the four tasks activated a set of largely overlapping, common brain areas: the sensorimotor and premotor cortices, the right inferior frontal gyrus, the supplementary motor area, the left parietal operculum and the adjacent inferior parietal lobule, the basal ganglia and the cerebellum. Second, differences between tasks were restricted to the bilateral auditory cortices and to the left ventrolateral sensorimotor cortex, with greater signal intensity for vowel vocalization. Finally, a dorso-ventral somatotopic organization of lip, jaw, vocalic/laryngeal, and tongue movements was observed within the primary motor and somatosensory cortices using individual region-of-interest (ROI) analyses. These results provide evidence for a core neural network involved in laryngeal and supralaryngeal motor control and further refine the sensorimotor somatotopic organization of orofacial articulators.     

A case of foreign accent syndrome resulting in regional dialect

BACKGROUND: Foreign Accent Syndrome (FAS) is a rare acquired syndrome following neurological damage that results in articulatory distortions that are commonly perceived as a "foreign" accent. The nature of the underlying deficit of FAS remains controversial. We present the first reported Canadian case study of FAS following a stroke. We describe a stroke patient, RD, who suffered an acute infarction to the left internal capsule, basal ganglia and frontal corona radiata. She was diagnosed as having FAS without any persistent aphasic symptoms. Family, friends, and health care professionals similarly described her speech as sounding like she had a Canadian East Coast accent, a reported change from her native Southern Ontario accent. METHOD: An investigation of this case was pursued, incorporating neuroimaging, neuropsychological and speech pathology assessments, and formalized linguistic analyses. RESULTS: Linguistic analyses confirmed that RD's speech does in fact have salient aspects of Atlantic Canadian English in terms of both prosodic and segmental characteristics. However, her speech is not entirely consistent with an Atlantic Canadian English accent. INTERPRETATION: The fact that RD's speech is perceived as a regional variant of her native language, rather than the "generic foreign accent" of FAS described elsewhere, suggests that the perceived "foreignness" in FAS is not primarily due to dysfluencies which indicate a non-native speaker, but rather due to very subtle motor-planning deficits which give rise to systemic changes in specific phonological segments. This has implications for the role of the basal ganglia in speech production.     

Neurophysiologic markers in laryngeal muscles indicate functional anatomy of laryngeal primary motor cortex and premotor cortex in the caudal opercular part of inferior frontal gyrus

ObjectiveThe aim of this study was to identify neurophysiologic markers generated by primary motor and premotor cortex for laryngeal muscles, recorded from laryngeal muscle.MethodsTen right-handed healthy subjects underwent navigated transcranial magnetic stimulation (nTMS) and 18 patients underwent direct cortical stimulation (DCS) over the left hemisphere, while recording neurophysiologic markers, short latency response (SLR) and long latency response (LLR) from cricothyroid muscle. Both healthy subjects and patients were engaged in the visual object-naming task. In healthy subjects, the stimulation was time-locked at 10–300 ms after picture presentation while in the patients it was at zero time.ResultsThe latency of SLR in healthy subjects was 12.66 ± 1.09 ms and in patients 12.67 ± 1.23 ms. The latency of LLR in healthy subjects was 58.5 ± 5.9 ms, while in patients 54.25 ± 3.69 ms. SLR elicited by the stimulation of M1 for laryngeal muscles corresponded to induced dysarthria, while LLR elicited by stimulation of the premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, corresponded to speech arrest in patients and speech arrest and/or language disturbances in healthy subjects.ConclusionIn both groups, SLR indicated location of M1 for laryngeal muscles, and LLR location of premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, while stimulation of these areas in the dominant hemisphere induced transient speech disruptions.SignificanceDescribed methodology can be used in preoperative mapping, and it is expected to facilitate surgical planning and intraoperative mapping, preserving these areas from injuries.     

Foreign accent syndrome and force of articulation

Background: Foreign accent syndrome (FAS) is a rare, acquired neurogenic disorder characterised by altered speech that sounds foreign, for example, English with a French accent. Several prosodic and acoustic changes have been mentioned in the literature, but none has indicated an underlying mechanism clarifying the accent in speech.

Aims: The present case study aims to capture the acoustic changes in the speech of a Dutch FAS speaker under one heading: increased force of articulation.

Methods & Procedures: Some of the often described characteristics of FAS concerning speech rate, stress patterns, vowel reduction, voice onset time (VOT) and assimilation were analysed in the speech of a Dutch male (AA) who speaks with a foreign accent after a stroke. Fifty-two students of Linguistics and Speech Therapy were asked to evaluate the accent of AA and came up with a variety of perceived accents, like Arabic, Turkish, German, Spanish and French.

Outcomes & Results: We argue that all investigated characteristics reveal an increase in force of articulation. The reported variation in perceived accents can be explained by a different focus on the variety of phonetic aspects of FAS related to the differences between the phonological systems of the perceived languages and Dutch.

Conclusions: Increased force of articulation may lead to the perception of different foreign accents in speakers with FAS. The specific accent depends on the focus of the listener on one of the phonetic aspects of force of articulation.     

Acoustic analyses of two recovered cases of foreign accent syndrome

Recently, a growing number of studies have been published involving phonetic and acoustic analyses on the rare motor-speech disorder known as Foreign Accent Syndrome (FAS). These studies have relied on pre- and post-trauma speech samples to investigate the acoustic and phonetic properties of individual cases of FAS speech. This study presents detailed acoustic analyses of the speech characteristics of two new cases of FAS using identical pre- and post-recovery speech samples, thus affording a new level of control in the study of Foreign Accent Syndrome. Participants include a 48-year-old female who began speaking with an “Eastern European” accent following a traumatic brain injury, and a 45-year-old male who presented with a “British” accent following a subcortical cerebral vascular accident (CVA). The acoustic analysis was based on 18 real words comprised of the stop consonants /p/, /t/, /k/; /b/, /d/, /g/ combined with the peripheral vowels /i/, /a/ and /u/ and ending in a voiceless stop. Computer-based acoustic measures included: (1) voice onset time (VOT), (2) vowel durations, (3) whole word durations, (4) first, second and third formant frequencies, and (5) fundamental frequency. Formant frequencies were measured at three points in the vowel duration: (a) 20%, (b) 50%, and (c) 80% to assess differences in vowel ‘onglides’ and ‘offglides’. The acoustic analysis allowed precise quantification of the major phonetic features associated with the foreign quality of participants' FAS speech. Results indicated post-recovery changes in both duration and frequency measures, including a tendency toward more normal VOT production of voiced stops, changes in average vowel durations, as well as evidence from formant frequency values of vowel backing for both participants. The implications of this study for future research and clinical applications are also considered.     

A case of foreign accent syndrome, with follow-up clinical, neuropsychological and phonetic descriptions

We report a comparatively 'pure' case of 'foreign accent syndrome' (FAS) in a right-handed patient who sustained a small, isolated, left basal ganglia infarct. At 3 weeks post-onset FAS persisted in the absence of aphasic disorder. Phonetic analysis of the patient's speech was undertaken at that time and a further, more detailed acoustic and phonetic investigation, was undertaken at 8 months. The validity and significance of the term 'FAS' is discussed.     

Neural bases of the foreign accent syndrome: A functional magnetic resonance imaging case study

Foreign accent syndrome (FAS) is a rare disorder characterized by the emergence of a perceived foreign accent following brain damage. Despite decades of study, little is known about the neural substrates involved in this disorder. In this case study, MRI images of the brain were obtained during a speech task for an American English-speaking monolingual female who presented with FAS of unknown etiology and was thought to sound ‘Swedish’ or ‘Eastern European’. On the basis of MR structural imaging, the patient was noted to have frontal lobe atrophy. An fMRI picture-naming task designed to broadly engage the speech motor network revealed predominantly left-hemisphere involvement, including activation of the (1) left superior temporal and medial frontal structures, (2) bilateral subcortical structures and thalamus, and (3) left cerebellum. The results suggest an instance of substantial brain reorganization for speech motor control.     

Neural bases of the foreign accent syndrome: a functional magnetic resonance imaging case study

Foreign accent syndrome (FAS) is a rare disorder characterized by the emergence of a perceived foreign accent following brain damage. Despite decades of study, little is known about the neural substrates involved in this disorder. In this case study, MRI images of the brain were obtained during a speech task for an American English-speaking monolingual female who presented with FAS of unknown etiology and was thought to sound 'Swedish' or 'Eastern European'. On the basis of MR structural imaging, the patient was noted to have frontal lobe atrophy. An fMRI picture-naming task designed to broadly engage the speech motor network revealed predominantly left-hemisphere involvement, including activation of the (1) left superior temporal and medial frontal structures, (2) bilateral subcortical structures and thalamus, and (3) left cerebellum. The results suggest an instance of substantial brain reorganization for speech motor control.     

A role for the cerebellum in motor speech planning: evidence from foreign accent syndrome

A 3 year follow-up study was performed in a patient with foreign accent syndrome (FAS) as the sole cognitive manifestation of a left fronto-parietal stroke. The hypothesis of involvement of the right cerebellum in this motor speech planning disorder was investigated by means of functional neuroimaging (SPECT) and neurobehavioral assessments. Based on the close parallelism between the evolution of FAS symptoms and the perfusional changes in the right cerebellum, it is argued that FAS may result from a disruption of a close functional interplay between the supra- and infratentorial speech centers involved in motor speech planning.     

Cortical stimulation mapping in a patient with foreign accent syndrome: case report

Foreign accent syndrome is a rare language output disorder characterized by changes in various speech features leading to a perceived foreign accent. There are few cases reported in the literature. Due to the rarity of this condition, information regarding the functional neuroanatomy of FAS is lacking. We present the case of a 60-year-old woman with a left anterior parietal lobe breast carcinoma metastasis who developed foreign accent syndrome (FAS). This patient presented to the emergency room with right upper extremity weakness, facial weakness, and altered speech. Neurological examination revealed the patient's speech to be dysarthric and accented, but otherwise appropriate. Brain magnetic resonance (MR) imaging demonstrated a 3cm x 3cm x 3cm lesion in the left anterior parietal lobe. The patient underwent craniotomy for resection of the mass. Intra-operative cortical stimulation mapping demonstrated the lesion to be confined to somatosensory cortex and gross total resection was performed. There were no new neurological deficits post-operatively. To our knowledge, this is a unique case of FAS due to breast carcinoma metastasis. Additionally, this is the first documented case of electrocortical function stimulation mapping of language and Rolandic cortex in a patient with FAS.     

Perception of foreign accent syndrome speech and its relation to segmental characteristics

Foreign accent syndrome (FAS) is an acquired neurogenic disorder characterized by altered speech that sounds foreign-accented. This study presents a British subject perceived to speak with an Italian (or Greek) accent after a brainstem (pontine) stroke. Native English listeners rated the strength of foreign accent and impairment they perceived in speech of the FAS subject, alongside that of two native English speakers and Italian, Greek, and French L2 speakers acting as controls. The FAS subject was perceived to be as foreign-sounding as the L2 control speakers, but was also perceived as mildly impaired. The FAS subject's own perception of accents was also explored and it was found that his ability to distinguish presence and absence of accent does not seem to be affected. The relationship between listeners' perceptions and features of the FAS speech is explored via correlational statistics and qualitative analysis. Impressionistic phonetic analysis, supplemented by acoustic analysis, confirmed a number of features consistent with a typical Italian (and also Greek) accent and the Italian and Greek L2 speakers. A pre-stroke and a post-stroke sample from the FAS subject were compared and the nature of post-stroke changes in segmental realizations is discussed.     

Premovement slow cortical potentials and required muscle force in self-paced hand movements in the monkey

Surface negative--deep positive, slowly increasing potentials prior to self-paced hand movements were recorded in the contralateral premotor, motor and somatosensory cortices, with chronically implanted electrodes. Such premovement slow potentials in the 3 cortical areas changed their magnitudes with the required muscle force in the hand movement, and the potentials in the different cortices appeared to differ slightly in the manner of change. These results may suggest that the EPSPs in the superficial parts of apical dendrites of cortical pyramidal neurons principally via certain thalamo-cortical projections are induced prior to movements in the cortices so as to adjust the required force on anticipation, and that the premotor, motor and somatosensory cortices play some different functional roles in preparatory processes for the movement performance.