Brain changes underlying progression of speech motor programming impairment

The characteristics and reproducibility of motor speech functional neuroimaging in healthy controls

Introduction

Functional magnetic resonance imaging (fMRI) can improve our understanding of neural processes subserving motor speech function. Yet its reproducibility remains unclear. This study aimed to evaluate the reproducibility of fMRI using a word repetition task across two time points.

Methods

Imaging data from 14 healthy controls were analysed using a multi-level general linear model.

Results

Significant activation was observed during the task in the right hemispheric cerebellar lobules IV-V, right putamen, and bilateral sensorimotor cortices. Activation between timepoints was found to be moderately reproducible across time in the cerebellum but not in other brain regions.

Discussion

Preliminary findings highlight the involvement of the cerebellum and connected cerebral regions during a motor speech task. More work is needed to determine the degree of reproducibility of speech fMRI before this could be used as a reliable marker of changes in brain activity.

Clinical and cortical trajectories in non-fluent primary progressive aphasia and Alzheimer's disease: A role for emotion processing

OBJECTIVES

To examine the clinical trajectories and neural correlates of cognitive and emotion processing changes in the non-fluent/agrammatic (nfvPPA) and the logopenic (lvPPA) variants of primary progressive aphasia (PPA).

DESIGN

Observational case-control longitudinal cohort study.

SETTING

Research clinic of frontotemporal dementia.

PARTICIPANTS

This study recruited 29 non-semantic PPA patients (15 nfvPPA and 14 lvPPA) and compared them with 15 Alzheimer's disease (AD) patients and 14 healthy controls.

MEASUREMENTS

Participants completed an annual assessment (median = 2 years; range = 1-5 years) of general cognition, emotion processing and structural MRI. Linear mixed effects models investigated clinical and imaging trajectories between groups.

RESULTS

Over time, lvPPA showed the greatest cognitive deterioration. In contrast, nfvPPA showed significant decline in emotion recognition, whereas AD showed preserved emotion recognition, even with disease progression. Importantly, lvPPA also developed emotion processing impairments, with disease progression. Both nfvPPA and lvPPA showed continuing cortical atrophy in hallmark language-processing regions associated with these syndromes, together with progressive involvement of the right hemisphere regions, mirroring left hemisphere atrophy patterns at presentation. Decline in emotion processing was associated with bilateral frontal atrophy in nfvPPA and right temporal atrophy in lvPPA.

CONCLUSIONS

Our results show divergent clinical courses in nfvPPA and lvPPA, with rapid cognitive and neural deterioration in lvPPA and emotion processing decline in both groups and support the concurrent assessment of cognition and emotion processing in the clinic to inform diagnosis and monitoring in the non-semantic variants of PPA.

Neural basis of speech and grammar symptoms in non-fluent variant primary progressive aphasia spectrum

The non-fluent/agrammatic variant of primary progressive aphasia (nfvPPA) is a neurodegenerative syndrome primarily defined by the presence of apraxia of speech (AoS) and/or expressive agrammatism. In addition, many patients exhibit dysarthria and/or receptive agrammatism. This leads to substantial phenotypic variation within the speech-language domain across individuals and time, in terms of both the specific combination of symptoms as well as their severity. How to resolve such phenotypic heterogeneity in nfvPPA is a matter of debate. 'Splitting' views propose separate clinical entities: 'primary progressive apraxia of speech' when AoS occurs in the absence of expressive agrammatism, 'progressive agrammatic aphasia' (PAA) in the opposite case, and 'AOS + PAA' when mixed motor speech and language symptoms are clearly present. While therapeutic interventions typically vary depending on the predominant symptom (e.g. AoS versus expressive agrammatism), the existence of behavioural, anatomical and pathological overlap across these phenotypes argues against drawing such clear-cut boundaries. In the current study, we contribute to this debate by mapping behaviour to brain in a large, prospective cohort of well characterized patients with nfvPPA (n = 104). We sought to advance scientific understanding of nfvPPA and the neural basis of speech-language by uncovering where in the brain the degree of MRI-based atrophy is associated with inter-patient variability in the presence and severity of AoS, dysarthria, expressive agrammatism or receptive agrammatism. Our cross-sectional examination of brain-behaviour relationships revealed three main observations. First, we found that the neural correlates of AoS and expressive agrammatism in nfvPPA lie side by side in the left posterior inferior frontal lobe, explaining their behavioural dissociation/association in previous reports. Second, we identified a 'left-right' and 'ventral-dorsal' neuroanatomical distinction between AoS versus dysarthria, highlighting (i) that dysarthria, but not AoS, is significantly influenced by tissue loss in right-hemisphere motor-speech regions; and (ii) that, within the left hemisphere, dysarthria and AoS map onto dorsally versus ventrally located motor-speech regions, respectively. Third, we confirmed that, within the large-scale grammar network, left frontal tissue loss is preferentially involved in expressive agrammatism and left temporal tissue loss in receptive agrammatism. Our findings thus contribute to define the function and location of the epicentres within the large-scale neural networks vulnerable to neurodegenerative changes in nfvPPA. We propose that nfvPPA be redefined as an umbrella term subsuming a spectrum of speech and/or language phenotypes that are closely linked by the underlying neuroanatomy and neuropathology.

Acoustic Analysis and Neuroimaging Correlates of Diadochokinetic Rates in Mild-Moderate Primary Progressive Apraxia of Speech

Speech rate can be judged clinically using diadochokinetic (DDK) tasks, such as alternating motion rates (AMR) and sequential motion rates (SMR). We evaluated whether acoustic AMR/SMR speech rates would differentiate primary progressive apraxia of speech (PPAOS) from healthy controls, and determined how DDK rates relate to phonetic and prosodic speech characteristics and brain metabolism on FDG-PET. Rate was calculated for each of three AMRs (repetitions of 'puh', 'tuh', and 'kuh') and for SMRs (repetitions of 'puhtuhkuh') for 27 PPAOS patients and 52 controls who underwent FDG-PET. PPAOS patients were slower than controls on all DDK tasks. All DDK rates correlated with apraxia of speech severity, with strongest associations with prosodic speech features. Slower DDK rates were associated with hypometabolism in the right cerebellar dentate and left supplementary motor area. Performance on AMR rate, not just SMR rate, may be impaired in mild PPAOS, but sensitivity and specificity require further study.

Longitudinal changes in functional connectivity in speech motor networks in apraxia of speech after stroke

Objective

The cerebral substrates of apraxia of speech (AOS) recovery remain unclear. Resting state fMRI post stroke can inform on altered functional connectivity (FC) within cortical language networks. Some initial studies report reduced FC between bilateral premotor cortices in patients with AOS, with lowest FC in patients with the most severe AOS. However, longitudinal FC studies in stroke are lacking. The aims of the present longitudinal study in early post stroke patients with AOS were (i) to compare connectivity strength in AOS patients to that in left hemisphere (LH) lesioned stroke patients without a speech-language impairment, (ii) to investigate the relation between FC and severity of AOS, aphasia and non-verbal oral apraxia (NVOA) and (iii) to investigate longitudinal changes in FC, from the subacute phase to the chronic phase to identify predictors of AOS recovery.

Methods

Functional connectivity measures and comprehensive speech-language assessments were obtained at 4 weeks and 6 months after stroke in nine patients with AOS after a LH stroke and in six LH lesioned stroke patients without speech-language impairment. Functional connectivity was investigated in a network for speech production: inferior frontal gyrus (IFG), anterior insula (aINS), and ventral premotor cortex (vPMC), all bilaterally to investigate signs of adaptive or maladaptive changes in both hemispheres.

Results

Interhemispheric vPMC connectivity was significantly reduced in patients with AOS compared to LH lesioned patients without speech-language impairment. At 6 months, the AOS severity was associated with interhemispheric aINS and vPMC connectivity. Longitudinal changes in FC were found in individuals, whereas no significant longitudinal change in FC was found at the group level. Degree of longitudinal AOS recovery was strongly associated with interhemispheric IFG connectivity strength at 4 weeks.

Conclusion

Early interhemispheric IFG connectivity may be a strong predictor of AOS recovery. The results support the importance of interhemispheric vPMC connection in speech motor planning and severity of AOS and suggest that also bilateral aINS connectivity may have an impact on AOS severity. These findings need to be validated in larger cohorts.

Barcelona scale for buccophonatory apraxia: Quantitative assessment tool

INTRODUCTION

Currently there is no tool to quantify buccophonatory apraxia to stratify, compare and monitor patients longitudinally in an objective manner. Our aim in this study is to create a quantitative scale for buccophonatory apraxia and evaluate it in patients with the non-fluent/grammatical variant of primary progressive aphasia (nfvPPA) and other neurodegenerative diseases that occur with speech and/or language problems.

METHODS

The scale was designed based on useful elements in the assessment of buccophonatory apraxia and the total was quantified in seconds. The scale was administered to 64 participants with diagnoses of: nfvPPA, semantic variant of primary progressive aphasia (svPPA), logopenic variant of primary progressive aphasia (lvPPA), Huntington's disease, Parkinson's disease, as well as a group of healthy controls.

RESULTS

Patients showed a significantly higher score compared to controls. The nfvPPA group had the highest mean score on the scale (429 seconds ± 278). The scale was useful to differentiate vnfPPA from svPPA and Parkinson's disease (area under curve [AUC] of 0.956 and 0.989, respectively), but less to differentiate it from Huntington's disease (AUC = 0.67) and lvPPA. There was a statistically significant relationship between total score and disease severity in nfvPPA (P < .029).

CONCLUSIONS

The Barcelona scale for buccophonatory apraxia could be useful to quantitatively evaluate buccophonatory apraxia in different neurodegenerative diseases, and compare patients, especially in nfvPPA.