Effects of stimulation of the subthalamic nucleus on naming and reading nouns and verbs in Parkinson's disease

Narrative analysis in individuals with Parkinson's disease following intensive voice treatment: secondary outcome variables from a randomized controlled trial

Communication is often impaired in individuals with Parkinson's disease (PD), typically secondary to sensorimotor deficits impacting voice and speech. Language may also be diminished in PD, particularly for production and comprehension of verbs. Evidence exists that verb processing is influenced by motor system modulation suggesting that verb deficits in PD are underpinned by similarities in the neural representations of actions that span motor and semantic systems. Conversely, subtle differences in cognition in PD may explain difficulty in processing of complex syntactic forms, which increases cognitive demand and is linked to verb use. Here we investigated whether optimizing motor system support for vocal function (improving loudness) affects change in lexical semantic, syntactic, or informativeness aspects of spoken discourse. Picture description narratives were compared for 20 Control participants and 39 with PD, 19 of whom underwent Lee Silverman Voice Treatment (LSVT LOUD®). Treated PD narratives were also contrasted with those of untreated PD and Control participants at Baseline and after treatment. Controls differed significantly from the 39 PD participants for verbs per utterance, but this difference was largely driven by untreated PD participants who produced few utterances but with verbs, inflating their verbs per utterance. Given intervention, there was a significant increase in vocal loudness but no significant changes in language performance. These data do not support the hypothesis that targeting this speech motor system results in improved language production. Instead, the data provide evidence of considerable variability in measures of language production across groups, particularly in verbs per utterance.

Speech, voice, and language outcomes following deep brain stimulation: A systematic review

BACKGROUND

Deep brain stimulation (DBS) reliably ameliorates cardinal motor symptoms in Parkinson's disease (PD) and essential tremor (ET). However, the effects of DBS on speech, voice and language have been inconsistent and have not been examined comprehensively in a single study.

OBJECTIVE

We conducted a systematic analysis of literature by reviewing studies that examined the effects of DBS on speech, voice and language in PD and ET.

METHODS

A total of 675 publications were retrieved from PubMed, Embase, CINHAL, Web of Science, Cochrane Library and Scopus databases. Based on our selection criteria, 90 papers were included in our analysis. The selected publications were categorized into four subcategories: Fluency, Word production, Articulation and phonology and Voice quality.

RESULTS

The results suggested a long-term decline in verbal fluency, with more studies reporting deficits in phonemic fluency than semantic fluency following DBS. Additionally, high frequency stimulation, left-sided and bilateral DBS were associated with worse verbal fluency outcomes. Naming improved in the short-term following DBS-ON compared to DBS-OFF, with no long-term differences between the two conditions. Bilateral and low-frequency DBS demonstrated a relative improvement for phonation and articulation. Nonetheless, long-term DBS exacerbated phonation and articulation deficits. The effect of DBS on voice was highly variable, with both improvements and deterioration in different measures of voice.

CONCLUSION

This was the first study that aimed to combine the outcome of speech, voice, and language following DBS in a single systematic review. The findings revealed a heterogeneous pattern of results for speech, voice, and language across DBS studies, and provided directions for future studies.

Interpretable speech features vs. DNN embeddings: What to use in the automatic assessment of Parkinson's disease in multi-lingual scenarios

Speech-based approaches for assessing Parkinson's Disease (PD) often rely on feature extraction for automatic classification or detection. While many studies prioritize accuracy by using non-interpretable embeddings from Deep Neural Networks, this work aims to explore the predictive capabilities and language robustness of both feature types in a systematic fashion. As interpretable features, prosodic, linguistic, and cognitive descriptors were adopted, while x-vectors, Wav2Vec 2.0, HuBERT, and TRILLsson representations were used as non-interpretable features. Mono-lingual, multi-lingual, and cross-lingual machine learning experiments were conducted leveraging six data sets comprising speech recordings from various languages: American English, Castilian Spanish, Colombian Spanish, Italian, German, and Czech. For interpretable feature-based models, the mean of the best F1-scores obtained from each language was 81% in mono-lingual, 81% in multi-lingual, and 71% in cross-lingual experiments. For non-interpretable feature-based models, instead, they were 85% in mono-lingual, 88% in multi-lingual, and 79% in cross-lingual experiments. Firstly, models based on non-interpretable features outperformed interpretable ones, especially in cross-lingual experiments. Specifically, TRILLsson provided the most stable and accurate results across tasks and data sets. Conversely, the two types of features adopted showed some level of language robustness in multi-lingual and cross-lingual experiments. Overall, these results suggest that interpretable feature-based models can be used by clinicians to evaluate the deterioration of the speech of patients with PD, while non-interpretable feature-based models can be leveraged to achieve higher detection accuracy.

Long-term neuropsychological outcomes of deep brain stimulation in early-stage Parkinson's disease

INTRODUCTION

The pilot trial of deep brain stimulation (DBS) in early-stage Parkinson's disease (PD) randomized 30 patients (medication duration 0.5-4 years; without dyskinesia or motor fluctuations) to receive optimal drug therapy alone (early ODT) or subthalamic nucleus (STN) DBS plus ODT (early DBS + ODT). This study reports long-term neuropsychological outcomes from the early DBS pilot trial.

METHODS

This is an extension of an earlier study that examined two-year neuropsychological outcomes in the pilot trial. The primary analysis was conducted on the five-year cohort (n = 28), and a secondary analysis was conducted on the 11-year cohort (n = 12). Linear mixed effects models for each analysis compared overall trend in outcomes for randomization groups. All subjects who completed the 11-year assessment were also pooled to evaluate long-term change from baseline.

RESULTS

There were no significant differences between groups in either the five- or 11-year analyses. Across all PD patients who completed the 11-year visit, there was significant decline in Stroop Color and Color-Word and Purdue Pegboard from baseline to 11 years.

CONCLUSIONS

Previous significant differences between the groups in phonemic verbal fluency and cognitive processing speed showing more decline for early DBS + ODT subjects one year after baseline diminished as PD progressed. No cognitive domains were worse for early DBS + ODT subjects compared to standard of care subjects. There were shared declines across all subjects on cognitive processing speed and motor control, likely reflecting disease progression. More study is needed to understand the long-term neuropsychological outcomes associated with early DBS in PD.

Deep Brain Stimulation Impact on Voice and Speech Quality in Parkinson's Disease: A Systematic Review

OBJECTIVE

Deep brain stimulation (DBS) has considerable efficacy for the motor dysfunction of idiopathic Parkinson's disease (PD) on patient quality of life. However, the benefit of DBS on voice and speech quality remains controversial. We carried out a systematic review to understand the influence of DBS on parkinsonian dysphonia and dysarthria.

DATA SOURCES

A PubMed/MEDLINE and Cochrane systematic review was carried out following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Population, Intervention, Comparison, Outcome, Timing, and Setting (PICOTS) statements.

REVIEW METHODS

Three investigators screened studies published in the literature from inception to May 2022. The following data were retrieved: age, demographic, sex, disease duration, DBS duration, DBS location, speech, and voice quality measurements.

RESULTS

From the 180 studies identified, 44 publications met the inclusion criteria, accounting for 866 patients. Twenty-nine studies focused on voice/speech quality in subthalamic DBS patients, and 6 included patients with stimulation of pallidal, thalamic, and zona incerta regions. Most studies (4/6) reported a deterioration of the vocal parameters on subjective voice quality evaluation. For speech, the findings were more contrasted. There was an important heterogeneity between studies regarding the voice and speech quality outcomes used to evaluate the impact of DBS on voice/speech quality.

CONCLUSION

The impact of DBS on voice and speech quality significantly varies between studies. The stimulated anatomical region may have a significant role since the stimulation of the pallidal area was mainly associated with voice quality improvement, in contrast with other regions. Future controlled studies comparing all region stimulation are needed to get reliable findings.

LEVEL OF EVIDENCE

Level III: evidence from evidence summaries developed from systematic reviews.

Subthalamic oscillatory activity during normal and impaired speech

OBJECTIVE

We studied the relationship between oscillatory activity in the subthalamic nucleus (STN) and speech production in order to better understand the functional role of the STN.

METHODS

We simultaneously recorded subthalamic local field potentials and audio recordings from 5 patients with Parkinson's disease while they performed verbal fluency tasks. We then analyzed the oscillatory signals present in the subthalamic nucleus during these tasks.

RESULTS

We report that normal speech leads to a suppression of subthalamic alpha and beta power. Contrarily, a patient with motor blocks during speech initiation showed a low beta power increase. We also report an increase in error rates in the phonemic non-alternating verbal fluency task during deep brain stimulation (DBS).

CONCLUSIONS

We confirm previous findings that intact speech leads to desynchronization in the beta range in the STN. The speech related narrowband beta power increase in a patient with speech problems suggests that exaggerated synchronization in this frequency band is associated with motor blocks during speech initiation. The increased number of errors in verbal fluency tasks during DBS might be caused by an impairment of the response inhibition network caused by stimulation of the STN.

SIGNIFICANCE

We suggest that the inability to attenuate beta activity during motor processes is associated with motor freezing across motor behaviours such as speech and gait, as previously shown for freezing of gait.

Multilingual evaluation of interpretable biomarkers to represent language and speech patterns in Parkinson's disease

Motor impairments are only one aspect of Parkinson's disease (PD), which also include cognitive and linguistic impairments. Speech-derived interpretable biomarkers may help clinicians diagnose PD at earlier stages and monitor the disorder's evolution over time. This study focuses on the multilingual evaluation of a composite array of biomarkers that facilitate PD evaluation from speech. Hypokinetic dysarthria, a motor speech disorder associated with PD, has been extensively analyzed in previously published studies on automatic PD evaluation, with a relative lack of inquiry into language and task variability. In this study, we explore certain acoustic, linguistic, and cognitive information encoded within the speech of several cohorts with PD. A total of 24 biomarkers were analyzed from American English, Italian, Castilian Spanish, Colombian Spanish, German, and Czech by conducting a statistical analysis to evaluate which biomarkers best differentiate people with PD from healthy participants. The study leverages conceptual robustness as a criterion in which a biomarker behaves the same, independent of the language. Hence, we propose a set of speech-based biomarkers that can effectively help evaluate PD while being language-independent. In short, the best acoustic and cognitive biomarkers permitting discrimination between experimental groups across languages were fundamental frequency standard deviation, pause time, pause percentage, silence duration, and speech rhythm standard deviation. Linguistic biomarkers representing the length of the narratives and the number of nouns and auxiliaries also provided discrimination between groups. Altogether, in addition to being significant, these biomarkers satisfied the robustness requirements.

STN-DBS affects language processing differentially in Parkinson's disease: Multiple-case MEG study

OBJECTIVES

In this study, we investigated the effects of bilateral and unilateral deep brain stimulation of the subthalamic nucleus (STN-DBS) in PD patients on neural responses associated with two aspects of spoken language processing: semantics of action-related verbs and morphosyntactic processing.

MATERIALS AND METHODS

Using a passive unattended paradigm to present spoken linguistic stimuli, we recorded magnetoencephalographic (MEG) responses in three PD patients in four DBS conditions: left unilateral STN-DBS, right unilateral STN-DBS, bilateral STN-DBS, and no STN-DBS. To ensure that any observed effects of DBS on the neuromagnetic responses could be attributed to the linguistic context per se and were not merely induced by the electrical stimulation, we assessed the effects of STN-DBS on linguistic contrasts within each stimulation condition. Hence, we contrasted the processing of action vs. abstract verbs as well as the processing of correct vs. incorrect morphosyntactic inflections within each DBS condition.

RESULTS

The results revealed that, compared to the DBS-off state, both bilateral and right unilateral stimulation of the STN yielded significant dissociations in the processing of action and abstract verbs, with greater neuromagnetic responses for action verbs compared to abstract verbs. For morphosyntax processing, only left unilateral stimulation yielded significant dissociations (relative to the DBS-off state), with greater neuromagnetic responses to the incorrect inflections compared to the correct inflections.

CONCLUSION

The results reflect differential effects of unilateral and bilateral STN-DBS on neuromagnetic responses associated with the processing of spoken language. They suggest that different specific aspects of linguistic information processing in PD are affected differently by STN-DBS.

The Effect of Deep Brain Stimulation of the Subthalamic Nucleus on Language Function in Parkinson's Disease: A Systematic Review

Purpose This systematic review focuses on the effect of bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) on language function in Parkinson's disease (PD). It fills an important gap in recent reviews by considering other language tasks in addition to verbal fluency. Method We critically and systematically reviewed the literature on studies that investigated the effect of bilateral STN-DBS on language function in PD. All studies included a matched PD control group who were on best medical treatment, with language testing at similar baseline and follow-up intervals as the DBS PD group. Results Thirteen identified studies included a form of a verbal fluency task, seven studies included picture naming, and only two studies included more language-oriented tasks. We found that verbal fluency was negatively affected after DBS, whereas picture naming was unaffected. Studies investigating individual change patterns using reliable change indices showed that individual variability is larger for picture naming than for verbal fluency. Conclusions Verbal fluency is the most frequently investigated aspect of language function. Our analysis showed a pattern of decline in verbal fluency across multiple studies after STN-DBS, whereas picture naming was unaffected. Data on more language-oriented tests in a large DBS sample and best medical treatment control group are sparse. The investigation of language function in PD after DBS requires sensitive language tests (with and without time pressure) and experimental designs as used in the studies reviewed here. Reliable change index statistics are a promising tool for investigating individual differences in performance after DBS. Supplemental Material https://doi.org/10.23641/asha.14794458.

Thalamic but Not Subthalamic Neuromodulation Simplifies Word Use in Spontaneous Language

Several investigations have shown language impairments following electrode implantation surgery for Deep Brain Stimulation (DBS) in movement disorders. The impact of the actual stimulation, however, differs between DBS targets with further deterioration in formal language tests induced by thalamic DBS in contrast to subtle improvement observed in subthalamic DBS. Here, we studied speech samples from interviews with participants treated with DBS of the thalamic ventral intermediate nucleus (VIM) for essential tremor (ET), or the subthalamic nucleus (STN) for Parkinson’s disease (PD), and healthy volunteers (each n = 13). We analyzed word frequency and the use of open and closed class words. Active DBS increased word frequency in case of VIM, but not STN stimulation. Further, relative to controls, both DBS groups produced fewer open class words. Whereas VIM DBS further decreased the proportion of open class words, it was increased by STN DBS. Thus, VIM DBS favors the use of relatively common words in spontaneous language, compatible with the idea of lexical simplification under thalamic stimulation. The absence or even partial reversal of these effects in patients receiving STN DBS is of interest with respect to biolinguistic concepts suggesting dichotomous thalamic vs. basal ganglia roles in language processing.

The influence of contextual constraint on verbal selection mechanisms and its neural correlates in Parkinson's disease

A small number of studies have described verbal selection deficits in Parkinson's disease (PD) when selection must occur among competing alternatives. However, these studies have largely focused on single-word processing, or have utilised sentence stems that carry high contextual constraint, thus reducing selection demands. The present study aimed to determine the influence of variable contextual constraint on the selection of a verbal response in PD. This was achieved using an adaption of the Hayling Sentence Completion Task whereby PD participants and matched controls were required to provide a single word to complete a cloze probability sentence stem that carried a low, medium, or high degree of contextual constraint. Results revealed no main effect of group in terms of response time or accuracy, though a group-by-condition interaction in accuracy was noted. This was characterised by a significant difference in accuracy between low and medium levels of constraint for control participants, but no significant difference for the PD group. Functional MRI data revealed marked between-group differences in underlying neural activity. The control group showed increased recruitment of the dorsal striatum and the vlPFC under conditions that placed greater demands upon selection (i.e. low and medium constraint), and greater activity overall in the left dlPFC and right vlPFC. However, in the PD group, behavioural performance appeared to be maintained despite underlying decreases in frontostriatal activity, suggesting other compensatory mechanisms that may include changes in functional connectivity or an over-medication effect in frontal networks in response to loss of signalling in cortico-subcortical pathways.

The effect of Subthalamic nucleus deep brain stimulation on verb and noun naming in Turkish-Speaking Parkinson's disease patients

Parkinson's disease (PD) is associated with an action language deficit. Subthalamic nucleus deep brain stimulation (STN DBS) deteriorates verbal fluency, but may improve verb naming more than nouns in PD. We investigated effects of grammatical class (verb vs noun), action content (action vs non-action) of words and unilateral, bilateral or no stimulation on naming. Nouns were named more accurately and faster by controls and PD participants; however the noun-verb difference was higher for PD participants. Language, executive and visuospatial function deficits in PD accounted for this difference between PD group and controls. Noun-verb difference was accounted by differences in imageability, familiarity and complexity of the stimuli. Non-action words were named more accurately than action words in the overall sample. Stimulation conditions did not have an effect on naming. This study in Turkish-speaking participants show an action language deficit due to underlying cognitive deficits without an STN DBS effect in PD.

Contribution of the Cerebellum and the Basal Ganglia to Language Production: Speech, Word Fluency, and Sentence Construction-Evidence from Pathology

Evidence reported in recent decades increasingly confirms that both the cerebellum and the basal ganglia, which are primarily involved in movement control, also have a significant role in a vast range of cognitive and affective functions. Evidence from pathology indicates that the disorders of some aspects of language production which follow damage of the cerebellum or respectively basal ganglia, i.e., disorders of speech, word fluency, and sentence construction, have identifiable neuropsychological profiles and that most manifestations can be specifically attributed to the dysfunctions of mechanisms supported by one or the other of these structures. The cerebellum and the basal ganglia are reciprocally interconnected. Thus, it is plausible that some disorders observed when damage involves one of these structures could be remote effects of abnormal activity in the other. However, in a purely clinical-neuropsychological perspective, primary and remote effects in the network are difficult to disentangle. Functional neuroimaging and non-invasive brain stimulation techniques likely represent the indispensable support for achieving this goal.

Why Language Processing Recruits Modality Specific Brain Regions: It Is Not About Understanding Words, but About Modelling Situations

Whether language comprehension requires the participation of brain structures that evolved for perception and action has been a subject of intense debate. While brain-imaging evidence for the involvement of such modality-specific regions has grown, the fact that lesions to these structures do not necessarily erase word knowledge has invited the conclusion that language-induced activity in these structures might not be essential for word recognition. Why language processing recruits these structures remains unanswered, however. Here, we examine the original findings from a slightly different perspective. We first consider the 'original' function of structures in modality-specific brain regions that are recruited by language activity. We propose that these structures help elaborate 'internal forward models' in motor control (c.f. emulators). Emulators are brain systems that capture the relationship between an action and its sensory consequences. During language processing emulators could thus allow accessing associative memories. We further postulate the existence of a linguistic system that exploits, in a rule-based manner, emulators and other nonlinguistic brain systems, to gain complementary (and redundant) information during language processing. Emulators are therefore just one of several sources of information. We emphasize that whether a given word-form triggers activity in modality-specific brain regions depends on the linguistic context and not on the word-form as such. The role of modality-specific systems in language processing is thus not to help understanding words but to model the verbally depicted situation by supplying memorized context information. We present a model derived from these assumptions and provide predictions and perspectives for future research.

Subthalamic nucleus activity in the processing of body and mental action verbs in people with Parkinson's disease

Local field potentials evoked by body action and mental action verbs were recorded in the subthalamic nucleus (STN) of 18 patients with Parkinson's disease through the electrodes implanted for deep brain stimulation. Compared with the medication on-condition, the medication off-condition showed a difference in activity in the early time segments, mainly in the right STN, with larger amplitudes for body action verbs. In the on-condition a similar pattern was detected in the left STN. These patterns of early differences in activity evoked by different types of verbs might indicate the potential of the STN to rapidly detect relevant behavioural clues in verbal content and to integrate these in subsequent cortico-subcortical interactions. In addition, these lateralizations allow speculations about shifts in processing activity correlating with dopaminergic denervation. Whether this detection relies on phonological, semantic or grammatical clues remains an open question.

A dissociation between syntactic and lexical processing in Parkinson's disease

Parkinson's disease (PD), which involves the degeneration of dopaminergic neurons in the basal ganglia, has long been associated with motor deficits. Increasing evidence suggests that language can also be impaired, including aspects of syntactic and lexical processing. However, the exact pattern of these impairments remains somewhat unclear, for several reasons. Few studies have examined and compared syntactic and lexical processing within subjects, so their relative deficits remain to be elucidated. Studies have focused on earlier stages of PD, so syntactic and lexical processing in later stages are less well understood. Research has largely probed English and a handful of other European languages, and it is unclear whether findings generalize more broadly. Finally, few studies have examined links between syntactic/lexical impairments and their neurocognitive substrates, such as measures of basal ganglia degeneration or dopaminergic processes. We addressed these gaps by investigating multiple aspects of Farsi syntactic and lexical processing in 40 Farsi native-speaking moderate-to-severe non-demented PD patients, and 40 healthy controls. Analyses revealed equivalent impairments of syntactic comprehension and syntactic judgment, across different syntactic structures. Lexical processing was impaired only for motor function-related objects (e.g., naming 'hammer', but not 'mountain'), in line with findings of PD deficits at naming action verbs as compared to objects, without the verb/noun confound. In direct comparisons between lexical and syntactic tasks, patients were better at naming words like 'mountain' (but not words like 'hammer') than at syntactic comprehension and syntactic judgment. Performance at syntactic comprehension correlated with the last levodopa equivalent dose. No other correlations were found between syntactic/lexical processing measures and either levodopa equivalent dose or hypokinesia, which reflects degeneration of basal ganglia motor-related circuits. All critical significant main effects, interactions, and correlations yielded large effect sizes. The findings elucidate the nature of syntactic and lexical processing impairments in PD.

Selection Processing in Noun and Verb Production in Left- and Right-Sided Parkinson's Disease Patients

Verbs are more difficult to produce than nouns. Thus, if executive resources are reduced as in Parkinson's disease (PD), verbs are penalized compared to nouns. However, in an experimental condition in which it is the noun that must be selected from a larger number of alternatives compared to the verb, it is the noun production that becomes slower and more prone to errors. Indeed, patients are slower and less accurate than normal subjects when required to produce nouns from verbs (VN) in a morphology derivation tasks (e.g., "osservazione" from "osservare") ["observation" from "observe"] than verbs from nouns in a morphology generation task, in which only a verb can be generated from the noun (NV) (e.g., "fallire" from "fallimento") ["to fail" from "failure"]. In the Italian language morphology, in fact, generation and derivation tasks differ in the number of lexical entries among which the response must be selected. The left Inferior Frontal Gyrus (IFG) has been demonstrated to be involved in selection processes. In the present study, we explored if the ability to select words is related to the cortical thickness of the left IFG. Twelve right-sided PD with nigrostriatal hypofunctionality in the left hemisphere (RPD-LH), 9 left-sided PD with nigrostriatal hypofunctionality in the right hemisphere (LPD-RH) and 19 healthy controls (HC) took part in the study. NV and VN production tasks were administered; accuracy and reaction times (RTs) were collected. All 40 subjects received a structural MRI examination. Cortical thickness of the IFG and volumetric measurements for subcortical regions, thought to support selection processes, were computed using FreeSurfer. In VN derivation tasks RPD-LH patients were less accurate than LPD-RH patients (accuracy: 66% vs. 77%). No difference emerged among the three groups in RTs. Task accuracy/RTs and IFG thickness showed a significant correlation only in RPD-LH. Not only nouns (as expected) but also verbs were correlated with cortical thickness. This suggests that the linguistic nature of the stimuli along with executive resources are both relevant during word selection processes. Our data confirm that executive resources and language interact in the left IFG in word production tasks.

Evaluation of Linguistic Markers of Word-Finding Difficulty and Cognition in Parkinson's Disease

PURPOSE

Early cognitive symptoms such as word-finding difficulty (WFD) in daily conversation are common in Parkinson's disease (PD), but studies have been limited by a lack of feasible, quantitative measures. Linguistic analysis, focused on pauses in speech, may yield markers of impairment of cognition and communication in PD. The objective of this study was to evaluate the relationship of linguistic markers in semistructured speech to WFD symptoms and cognitive function in PD.

METHOD

Speech recordings of description of the Cookie Theft picture in 53 patients with PD without dementia and 23 elderly controls were analyzed with Praat software. Montreal Cognitive Assessment (MoCA; Nasreddine et al., 2005), category naming fluency, and confrontation naming tests were administered. Questionnaires rating WFD symptoms and cognitive instrumental activities of daily living were completed. We determined the relationships between (a) pause length and location, (b) MoCA score, and (c) WFD symptoms, using Pearson's correlations and multivariate regression models.

RESULTS

Compared with controls, patients with PD had more pauses within utterances as well as fewer words per minute and a lower percentage of well-formed sentences. Pauses within utterances differed significantly between PD-mild cognitive impairment and normal cognition (p < .001). Words per minute and percentage of well-formed sentences were predictive of MoCA in multivariate regression models. Pauses before verbs were associated with patient-reported severity of WFD symptoms (p = .006).

CONCLUSIONS

Linguistic markers including pauses within utterances distinguish patients with PD with mild cognitive symptoms from elderly controls. These markers are associated with global cognitive function before the onset of dementia. Pauses before verbs and grammatical markers may index early cognitive symptoms such as WFD that may interfere with functional communication.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.6615401.

Evidence of semantic processing impairments in behavioural variant frontotemporal dementia and Parkinson's disease

PURPOSE OF REVIEW

Category-specific impairments caused by brain damage can provide important insights into how semantic concepts are organized in the brain. Recent research has demonstrated that disease to sensory and motor cortices can impair perceptual feature knowledge important to the representation of semantic concepts. This evidence supports the grounded cognition theory of semantics, the view that lexical knowledge is partially grounded in perceptual experience and that sensory and motor regions support semantic representations. Less well understood, however, is how heteromodal semantic hubs work to integrate and process semantic information.

RECENT FINDINGS

Although the majority of semantic research to date has focused on how sensory cortical areas are important for the representation of semantic features, new research explores how semantic memory is affected by neurodegeneration in regions important for semantic processing. Here, we review studies that demonstrate impairments to abstract noun knowledge in behavioural variant frontotemporal degeneration (bvFTD) and to action verb knowledge in Parkinson's disease, and discuss how these deficits relate to disease of the semantic selection network.

SUMMARY

Findings demonstrate that semantic selection processes are supported by the left inferior frontal gyrus (LIFG) and basal ganglia, and that disease to these regions in bvFTD and Parkinson's disease can lead to categorical impairments for abstract nouns and action verbs, respectively.

Cognitive Impact of Deep Brain Stimulation on Parkinson's Disease Patients

Subthalamic nucleus (STN) or globus pallidus interna (GPi) deep brain stimulation (DBS) is considered a robust therapeutic tool in the treatment of Parkinson's disease (PD) patients, although it has been reported to potentially cause cognitive decline in some cases. We here provide an in-depth and critical review of the current literature regarding cognition after DBS in PD, summarizing the available data on the impact of STN and GPi DBS as monotherapies and also comparative data across these two therapies on 7 cognitive domains. We provide evidence that, in appropriately screened PD patients, worsening of one or more cognitive functions is rare and subtle after DBS, without negative impact on quality of life, and that there is very little data supporting that STN DBS has a worse cognitive outcome than GPi DBS.

Production of verbs related to body movement in amyotrophic lateral sclerosis (ALS) and Parkinson's Disease (PD)

Theories of grounded cognition propose that action verb knowledge relies in part on motor processing regions, including premotor cortex. Accordingly, impaired action verb knowledge in patients with amyotrophic lateral sclerosis (ALS) and Parkinson's Disease (PD) is thought to be due to motor system degeneration. Upper motor neuron disease in ALS degrades the motor cortex and related pyramidal motor system, while disease in PD is centered in the basal ganglia and can spread to frontostriatal areas that are important to language functioning. These anatomical distinctions in disease may yield subtle differences in the action verb impairment between patient groups. Here we compare verbs where the body is the agent of the action to verbs where the body is the theme. To examine the role of motor functioning in body verb production, we split patient groups into patients with high motor impairment (HMI) and those with low motor impairment (LMI), using disease-specific measures of motor impairment. Regression analyses assessed how verb production in ALS and PD was related to motor system atrophy. We find a dissociation between agent- and theme-body verbs in ALS: ALS HMI were impaired for agent body verbs but not theme verbs, compared to ALS LMI. This dissociation was not present in PD patients, who instead show depressed production for all body verbs. Although patients with cognitive impairment were excluded from this study, cognitive performance significantly correlated with the production of theme verbs in ALS and cognitive/stative verbs in PD. Finally, regression analyses related the agent-theme dissociation in ALS to grey matter atrophy of premotor cortex. These findings support the view that motor dysfunction and disease in premotor cortex contributes to the agent body verb deficit in ALS, and begin to identify some distinct characteristics of impairment for verbs in ALS and PD.

Word selection processing in Parkinson's disease: When nouns are more difficult than verbs

Patients with Parkinson's disease (PD) are impaired in verb production. Interpretations range from grammatical deficits to semantic-conceptual decay of action representation. The verb production deficit in PD can also be considered a dysexecutive disorder, specifically, a deficit of selection processing during word production, due to corticostriatal damage. Producing verbs is "more difficult" than producing nouns, because verb-forms must be selected from a large set of word-forms which share the verb-root, and the set of possible verb-forms is larger than the set of possible noun-forms when a noun has to be produced. However, if we devise a condition in which a noun must be selected from a set of alternatives larger than the set of alternative forms from which a verb must be selected, we expect an opposite pattern, with nouns becoming more difficult than verbs. We used morphological tasks varying in the number of alternative responses during word production. Fourteen PD patients and 14 healthy Controls participated in the study. Participants performed a noun-from-verb ('observation' from 'to observe') and a noun-from adjective derivation task ('kindness' from 'kind'), and a verb-from-noun ('to observe' from 'observation') and an adjective-from-noun generation task ('kind' from 'kindness'). Input-stimuli were presented singularly on a screen and participants produced the response as fast as possible. Response latencies were longer in derivation tasks (several alternative responses) than in generation tasks (one possible response), irrespective of the grammatical class of the target word, with no difference between groups. PD patients were significantly less accurate than Controls only in the noun-from-verb derivation task, that is, in the task with the highest number of alternative responses (PD: 60%; Controls: 81%). Results suggest that the verb production disorder in PD patients may reflect disturbed selection processes among competitors: the higher the number of alternative responses the more severe the impairment.

The role of the motor system in action naming in patients with neurodegenerative extrapyramidal syndromes

Previous studies of patients with brain damage have suggested a close relationship between aphasia and movement disorders. Neurodegenerative extrapyramidal syndromes associated with cognitive impairment provide an interesting model for studying the neural substrates of cognitive and motor symptoms. In this review, we focused on studies investigating language production abilities in patients with Parkinson's disease (PD), Corticobasal Syndrome (CBS) and Progressive Supranuclear Palsy (PSP). According to some reports, these patients exhibit a reduction in performance in both action and object naming or verb production compared to healthy individuals. Furthermore, a disproportional impairment of action naming compared to object naming was systematically observed in patients with these disorders. The study of these clinical conditions offers the unique opportunity to examine the close link between linguistic features and motor characteristics of action. This particular pattern of language impairment may contribute to the debate on embodiment theory and on the involvement of the basal ganglia in language and in integrating language and movement. From a translational perspective, we suggest that language ability assessments are useful in the clinical work-up, along with neuropsychological and motor evaluations. Specific protocols should be developed in the near future to better characterize language deficits and to permit an early cognitive diagnosis. Moreover, the link between language deficits and motor impairment opens a new issue for treatment approaches. Treatment of one of these two symptoms may ameliorate the other, and treating both may produce a greater improvement in patients' global clinical conditions.

Lexical-retrieval and semantic memory in Parkinson's disease: The question of noun and verb dissociation

The dissociation between the processing of verbs and nouns has been debated in light of the Embodied Cognition Theory (EC). The objective of this paper is to verify how action and verb processing deficits of PD patients are modulated by different tasks with different cognitive demands. Action and object lexical-semantic processing was evaluated in patients with Parkinson's Disease (PD) and cognitively healthy controls through three different tasks (verbal fluency, naming and semantic association). Compared to controls, PD patients presented worse performance in naming actions and in the two semantic association tasks (action/object). Action verbal fluency performance was significantly associated with PD severity whereas object semantic association deficits and noun verbal fluency scores were associated to lower scores in measures of global cognitive functioning. Our data suggest that semantic deficits are related to the type of cognitive processing and this is in the line with more flexible EC accounts.

Aspects of oral communication in patients with Parkinson's disease submitted to Deep Brain Stimulation

INTRODUCTION

Deep Brain Stimulation (DBS) has been satisfactorily used to control the cardinal motor symptoms of Parkinson's disease (PD), but little is known about its impact on communication.

PURPOSE

This study aimed to characterize the aspects of cognition, language, speech, voice, and self-perception in two patients with PD, pre- and post- DBS implant surgery.

METHODS

The patients were assessed using a cognitive screening test, a brief language evaluation, a self-declared protocol, and an analysis of the aspects of voice and speech, which was conducted by a specialized Speech-language Therapist who was blinded for the study.

RESULTS

At the pre-surgery assessment, Case I showed impairment regarding the aspects of cognition, language and voice, whereas Case II showed impairment only with respect to the voice aspect. The post-surgery evaluation of the cases showed an opposite pattern of the effect of DBS after analysis of the communication data: Case I, who presented greater impairment before the surgery, showed improvement in some aspects; Case II, who presented lower communicative impairment before the surgery, showed worsening in other aspects.

CONCLUSION

This study shows that DBS may influence different communication aspects both positively and negatively. Factors associated with the different effects caused by DBS on the communication of patients with PD need to be further investigated.

Subthalamic nucleus stimulation and spontaneous language production in Parkinson's disease: A double laterality problem

BACKGROUND

Asymmetric degeneration of dopaminergic neurons, are characteristic for Parkinson's disease (PD). Despite the lateralized representation of language, the correlation of asymmetric degeneration of nigrostriatal networks in PD with language performance has scarcely been examined.

OBJECTIVE/HYPOTHESIS

The laterality of dopamine depletion influences language deficits in PD and thus modulates the effects of subthalamic nucleus (STN) stimulation on language production.

METHODS

The spontaneous language production of patients with predominant dopamine depletion of the left (PD-left) and right (PD-right) hemisphere was compared in four stimulation conditions.

RESULTS

PD-right made comparatively more verb inflection errors than PD-left. Bilateral STN stimulation improves spontaneous language production only for PD-left.

CONCLUSIONS

The laterality of dopamine depletion influences spontaneous language production and the effect of STN stimulation on linguistic functions. However, it is probably only one of the many variables influencing the effect of STN stimulation on language production.

The effects of subthalamic deep brain stimulation on metaphor comprehension and language abilities in Parkinson's disease

The effects of subthalamic nucleus (STN) deep brain stimulation (DBS) in Parkinson's disease (PD) on different language abilities are still controversial and its impact on high-level language abilities such as metaphor comprehension has been overlooked. The aim of this study was to determine the effects of STN electrical stimulation on metaphor comprehension and language abilities such as lexical and semantic capacities. Eight PD individuals with bilateral STN-DBS were first evaluated OFF-DBS and, at least seven weeks later, ON-DBS. Performance on metaphor comprehension, lexical decision, word association and verbal fluency tasks were compared ON and OFF-DBS in addition to motor symptoms evaluation. STN stimulation had a significant beneficial effect on motor symptoms in PD. However, this stimulation did not have any effect on metaphor comprehension or any other cognitive ability evaluated in this study. These outcomes suggest that STN stimulation may have dissociable effects on motor and language functions.

Action/Verb processing: Debates in neuroimaging and the contribution of studies in patients with Parkinson's disease

The objective of the current review was to verify whether studies investigating lexical-semantic difficulties in patients with Parkinson's disease (PD) support the Embodied Cognition model. Under this framework, it is predicted that patients with PD will have more difficulties in the semantic processing of action concepts (action verbs) than of motionless objects. We also verified how and whether these studies are following current debates of Neuroscience, particularly the debate between the Lexical and the Embodied Cognition models. Recent neuroimaging studies on the neural basis of the semantics of verbs were presented, as well as others that focused on the neural processing of verbs in PD. We concluded that few studies suitably verified the Embodied Cognition theory in the context of PD, especially using neuroimaging techniques. These limitations show there is much to investigate on the semantic difficulties with action verbs in these patients, where it is particularly important to control for psycholinguistic variables and the inherent semantic characteristics of verbs in future studies.

Words in motion: Motor-language coupling in Parkinson’s disease

A growing body of evidence indicates that neurodegenerative motor disorders involved high-order cognitive dysfunctions. Crucially, evidence obtained in multiple behavioral, neuroimaging, and electrophysiological studies points to selective impairments of action language -that is, processing of linguistic stimuli denoting motor actions, including idioms (e.g., cut a rug) and action verbs (e.g., clap). Action-verb deficits (with relative preservation of noun processing) have been repeatedly documented in Parkinson’s disease (PD). However, research on relevant biomarkers is still scant, and clinical implications of these findings have not yet been formally discussed. Relevant insights may be obtained through the assessment of motor-language coupling (i.e., the behavioral and neural integration of action-verb processing and ongoing motor actions). We propose that motorlanguage coupling deficits, as indexed by a cortical-subcortical network, may constitute an early neurocognitive marker of PD. Specifically, deficits in this domain at the prodromal stage may be detected through the actionsentence compatibility (ACE) paradigm, which induces a contextual coupling of ongoing motor actions and action-verb processing. Our translational proposal is supported and illustrated by recent studies demonstrating the sensitivity of the ACE technique as well as its potential to assist in differential diagnosis and interventionprogram design.