Declines in switching underlie verbal fluency changes after unilateral pallidal surgery in Parkinson's disease

Neuropsychological Rehabilitation Improves Memory and Action Naming in Patients With Post-COVID-19 Syndrome

PURPOSE

Post-COVID-19 syndrome (PCS-19) is a condition characterized by both physical and cognitive alterations in patients who have overcome COVID-19. Despite the high incidence of this disorder and the inconveniences it produces to those affected, there are few studies investigating the efficacy of cognitive stimulation in these patients. The aim of this study was to compare two groups of patients with PCS-19. One of them was treated with neuropsychological intervention for 6 months, whereas the other did not receive treatment. Both groups shared similar clinical characteristics and cognitive profiles.

METHOD

The study included 15 participants. Eight (seven women and one man, with a mean age of 50.13 years) made up the experimental group and received neuropsychological rehabilitation sessions once a week with the aim of recovering or compensating for their impaired functions. The control group consisted of seven patients (six women and one man, with a mean age of 52.86 years) who did not undergo neuropsychological rehabilitation sessions. The neuropsychological assessment protocol included tests for all cognitive domains.

RESULTS

In comparison with the assessment prior to the neuropsychological intervention, significant differences were found in the experimental group both in verbal memory and in the action naming task. As for the control group, improvements in action fluency performance were observed. Neither group showed significant improvement in pre- versus posttest Stroop scores. However, the control group did perform higher than the treatment group in the final assessment.

CONCLUSION

Despite the small sample size, our results suggest that patients with PCS-19 may benefit from neuropsychological rehabilitation, as it may help them to improve several cognitive functions that do not recover spontaneously.

Lateralized effects of deep brain stimulation in Parkinson's disease: evidence and controversies

The bilateral effects of deep brain stimulation (DBS) on motor and non-motor symptoms of Parkinson's disease (PD) have been extensively studied and reviewed. However, the unilateral effects-in particular, the potential lateralized effects of left- versus right-sided DBS-have not been adequately recognized or studied. Here we summarized the current evidence and controversies in the literature regarding the lateralized effects of DBS on motor and non-motor outcomes in PD patients. Publications in English language before February 2021 were obtained from the PubMed database and included if they directly compared the effects of unilateral versus contralateral side DBS on motor or non-motor outcomes in PD. The current literature is overall of low-quality and is biased by various confounders. Researchers have investigated mainly PD patients receiving subthalamic nucleus (STN) DBS while the potential lateralized effects of globus pallidus interna (GPi) DBS have not been adequately studied. Evidence suggests potential lateralized effects of STN DBS on axial motor symptoms and deleterious effects of left-sided DBS on language-related functions, in particular, the verbal fluency, in PD. The lateralized DBS effects on appendicular motor symptoms as well as other neurocognitive and neuropsychiatric domains remain inconclusive. Future studies should control for varying methodological approaches as well as clinical and DBS management heterogeneities, including symptom laterality, stimulation parameters, location of active contacts, and lead trajectories. This would contribute to improved treatment strategies such as personalized target selection, surgical planning, and postoperative management that ultimately benefit patients.

Deep brain stimulation effects on verbal fluency dissociated by target and active contact location

OBJECTIVE

Deep brain stimulation (DBS) improves motor symptoms in Parkinson's disease (PD), but it can also disrupt verbal fluency with significant costs to quality of life. The current study investigated how variability of bilateral active electrode coordinates along the superior/inferior, anterior/posterior, and lateral/medial axes in the subthalamic nucleus (STN) or the globus pallidus interna (GPi) contribute to changes in verbal fluency. We predicted that electrode location in the left hemisphere would be linked to changes in fluency, especially in the STN.

METHODS

Forty PD participants treated with bilateral DBS targeting STN (n = 23) or GPi (n = 17) completed verbal fluency testing in their optimally treated state before and after DBS therapy. Normalized atlas coordinates from left and right active electrode positions along superior/inferior, anterior/posterior, and lateral/medial axes were used to predict changes in fluency postoperatively, separately for patients with STN and GPi targets.

RESULTS

Consistent with prior studies, fluency significantly declined pre- to postsurgery (in both DBS targets). In STN-DBS patients, electrode position along the inferior to superior axis in the left STN was a significant predictor of fluency changes; relatively more superior left active electrode was associated with the largest fluency declines in STN. Electrode coordinates in right STN or GPi (left or right) did not predict fluency changes.

INTERPRETATION

We discuss these findings in light of putative mechanisms and potential clinical impact.

Recruiting the right hemisphere: Sex differences in inter-hemispheric communication during semantic verbal fluency

Sex differences in cognitive functions are heavily debated. Recent work suggests that sex differences do stem from different processing strategies utilized by men and women. While these processing strategies are likely reflected in different brain networks, so far the link between brain networks and processing strategies remains speculative. In the present study we seek for the first time to link sex differences in brain activation patterns to sex differences in processing strategies utilizing a semantic verbal fluency task in a large sample of 35 men and 35 women, all scanned thrice. For verbal fluency, strategies of clustering and switching have been described. Our results show that men show higher activation in the brain network supporting clustering, while women show higher activation in the brain network supporting switching. Furthermore, converging evidence from activation results, lateralization indices and connectivity analyses suggests that men recruit the right hemisphere more strongly during clustering, but women during switching. These results may explain findings of differential performance and strategy-use in previous behavioral studies.

The Role of Verb Fluency in the Detection of Early Cognitive Impairment in Alzheimer's Disease

BACKGROUND

Verb fluency (VF) is the less commonly used fluency test, despite several studies suggesting its potential as a neuropsychological assessment tool.

OBJECTIVE

To investigate the presence of VF deficits in mild cognitive impairment (MCI) and mild Alzheimer's disease (AD) dementia; to assess the usefulness of VF in the detection of cognitively healthy (CH) people who will convert to MCI, and from MCI to dementia; and to establish the VF cut-offs useful in the cognitive assessment of Spanish population.

METHODS

568 CH, 885 MCI, and 367 mild AD dementia individuals were administered the VF test and a complete neuropsychological battery. Longitudinal analyses were performed in 231 CH and 667 MCI subjects to search for VF predictors of diagnosis conversion.

RESULTS

A worsening on VF performance from CH, MCI to AD dementia groups was found. Lower performances on VF were significantly related to conversion from CH to MCI/MCI to dementia. When the effect of time to conversion was analyzed, a significant effect of VF was found on the faster conversion from CH to MCI, but not from MCI to dementia. Moreover, VF cut-off scores and sensitivity/specificity values were calculated for 6 conditions (3 age ranges by 2 educational levels).

CONCLUSION

The VF test may be a useful tool for the differential diagnosis of cognitive failure in the elderly. Since VF deficits seem to take place in early stages of the disease, it is a suitable neuropsychological tool for the detection not only of CH people who will convert to MCI, but also from MCI to dementia.

Standardised Neuropsychological Assessment for the Selection of Patients Undergoing DBS for Parkinson's Disease

DBS is an increasingly offered advanced treatment for Parkinson's disease (PD). Neuropsychological assessment is considered to be an important part of the screening for selection of candidates for this treatment. However, no standardised screening procedure currently exists. In this study, we examined the use of our standardised neuropsychological assessment for the evaluation of surgical candidates and to identify risk factors for subsequent decline in cognition and mood. A total of 40 patients were assessed before and after DBS. Evaluation of mood and case notes review was also undertaken. Before DBS, patients with PD demonstrated frequent impairments in intellectual functioning, memory, attention, and executive function, as well as high rates of mood disorder. Post-DBS, there was a general decline in verbal fluency only, and in one patient, we documented an immediate and irreversible global cognitive decline, which was associated with older age and more encompassing cognitive deficits at baseline. Case note review revealed that a high proportion of patients developed mood disorder, which was associated with higher levels of depression at baseline and greater reduction in levodopa medication. We conclude that our neuropsychological assessment is suitable for the screening of candidates and can identify baseline risk factors, which requires careful consideration before and after surgery.

Psychiatric and Cognitive Effects of Deep Brain Stimulation for Parkinson's Disease

Deep brain stimulation (DBS) is effective for Parkinson's disease (PD), dystonia, and essential tremor (ET). While motor benefits are well documented, cognitive and psychiatric side effects from the subthalamic nucleus (STN) and globus pallidus interna (GPi) DBS for PD are increasingly recognized. Underlying disease, medications, microlesions, and post-surgical stimulation likely all contribute to non-motor symptoms (NMS).

Thalamic deep brain stimulation decelerates automatic lexical activation

BACKGROUND

Deep Brain Stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) is a therapeutic option for patients with essential tremor. Despite a generally low risk of side effects, declines in verbal fluency (VF) have previously been reported.

OBJECTIVES

We aimed to specify effects of VIM-DBS on major cognitive operations needed for VF task performance, represented by clusters and switches. Clusters are word production spurts, thought to arise from automatic activation of associated information pertaining to a given lexical field. Switches are slow word-to-word transitions, presumed to indicate controlled operations for stepping from one lexical field to another.

PATIENTS & METHODS

Thirteen essential tremor patients with VIM-DBS performed verbal fluency tasks in their VIM-DBS ON and OFF conditions. Clusters and switches were formally defined by mathematical criteria. All results were compared to those of fifteen healthy control subjects, and significant OFF-ON-change scores were correlated to stimulation parameters.

RESULTS

Patients produced fewer words than healthy controls. DBS ON compared to DBS OFF aggravated this deficit by prolonging the intervals between words within clusters, whereas switches remained unaffected. This stimulation effect correlated with more anterior electrode positions.

CONCLUSION

VIM-DBS seems to influence word output dynamics during verbal fluency tasks on the level of word clustering. This suggests a perturbation of automatic lexical co-activation by thalamic stimulation, particularly if delivered relatively anteriorly. The findings are discussed in the context of the hypothesized role of the thalamus in lexical processing.

Effect of deep brain stimulation on speech performance in Parkinson's disease

Deep brain stimulation (DBS) has been reported to be successful in relieving the core motor symptoms of Parkinson's disease (PD) and motor fluctuations in the more advanced stages of the disease. However, data on the effects of DBS on speech performance are inconsistent. While there are some series of patients documenting that speech function was relatively unaffected by DBS of the nucleus subthalamicus (STN), other investigators reported on improvements of distinct parameters of oral control and voice. Though, these ameliorations of single speech modalities were not always accompanied by an improvement of overall speech intelligibility. On the other hand, there are also indications for an induction of dysarthria as an adverse effect of STN-DBS occurring at least in some patients with PD. Since a deterioration of speech function has more often been observed under high stimulation amplitudes, this phenomenon has been ascribed to a spread of current-to-adjacent pathways which might also be the reason for the sporadic observation of an onset of dysarthria under DBS of other basal ganglia targets (e.g., globus pallidus internus/GPi or thalamus/Vim). The aim of this paper is to review and evaluate reports in the literature on the effects of DBS on speech function in PD.

Effects of deep brain stimulation in the caudal zona incerta on verbal fluency

BACKGROUND

Deep brain stimulation (DBS) of the caudal zona incerta (cZi) is a relatively unexplored and promising treatment in patients with severe essential tremor (ET). Preliminary data further indicate that the ability to produce language may be slightly affected by the treatment.

OBJECTIVE

To evaluate the effects on verbal fluency following cZi DBS in patients with ET.

METHOD

Seventeen consecutive patients who had undergone DBS of the cZi for ET were tested regarding verbal fluency before surgery, 3 days after surgery and after 1 year. Ten patients were also evaluated by comparing performance on versus off stimulation after 1 year.

RESULTS

The total verbal fluency score decreased slightly, but significantly, from 22.7 (SD = 10.9) before surgery to 18.1 (SD = 7.5) 3 days after surgery (p = 0.036). After 1 year the score was nonsignificantly decreased to 20.1 (SD = 9.7, p = 0.2678). There was no detectable difference between stimulation on and off after 1 year.

CONCLUSION

There was a tendency of an immediate and mostly transient postoperative decline in verbal fluency following cZi DBS for ET. In some of the patients this reduction was, however, more pronounced and also sustained over time.

Dopamine regulation of human speech and bird song: a critical review

To understand the neural basis of human speech control, extensive research has been done using a variety of methodologies in a range of experimental models. Nevertheless, several critical questions about learned vocal motor control still remain open. One of them is the mechanism(s) by which neurotransmitters, such as dopamine, modulate speech and song production. In this review, we bring together the two fields of investigations of dopamine action on voice control in humans and songbirds, who share similar behavioral and neural mechanisms for speech and song production. While human studies investigating the role of dopamine in speech control are limited to reports in neurological patients, research on dopaminergic modulation of bird song control has recently expanded our views on how this system might be organized. We discuss the parallels between bird song and human speech from the perspective of dopaminergic control as well as outline important differences between these species.

Increased dependence of action selection on recent motor history in Parkinson's disease

It is well known that the basal ganglia are involved in switching between movement sequences. Here we test the hypothesis that this contribution is an instance of a more general role of the basal ganglia in selecting actions that deviate from the context defined by the recent motor history, even when there is no sequential structure to learn or implement. We investigated the effect of striatal dopamine depletion [in Parkinson's disease (PD)] on the ability to switch between independent action plans. PD patients with markedly lateralized signs performed a hand laterality judgment task that involved action selection of their most and least affected hand. Trials where patients selected the same (repeat) or the alternative (switch) hand as in a previous trial were compared, and this was done separately for the most and least affected hand. Behaviorally, PD patients showed switch-costs that were specific to the most affected hand and that increased with disease severity. Functional magnetic resonance imaging (fMRI) showed that this behavioral effect was related to the state of the frontostriatal system: as disease severity increased, contributions of the basal ganglia to the selection process and their effective connectivity with the medial frontal cortex (MFC) decreased, whereas involvement of the MFC increased. We conclude that the basal ganglia are important for rapidly switching toward novel motor plans even when there is no sequential structure to learn or implement. The enhanced MFC activity may result either from reduced focusing abilities of the basal ganglia or from compensatory processes.

Cognition following bilateral deep brain stimulation surgery of the subthalamic nucleus for Parkinson's disease

OBJECTIVE

Parkinson's disease (PD) is a neurodegenerative disorder characterized by significant motor dysfunction and various non-motor disturbances, including cognitive alterations. Deep brain stimulation (DBS) is an increasingly utilized therapeutic option for patients with PD that yields remarkable success in alleviating disabling motor symptoms. DBS has additionally been associated with changes in cognition, yet the evidence is not consistent across studies. The following review sought to provide a clearer understanding of the various cognitive sequelae of bilateral subthalamic nucleus (STN) DBS while taking into account corresponding neuroanatomy and potential confounding variables.

DESIGN

A literature search was performed using the following inclusion criteria: (1) at least five subjects followed for a mean of at least 3 months after surgery; (2) pre- and postoperative cognitive data using at least one standardized measure; (3) adequate report of study results using means and standard deviations.

RESULTS

Two recent meta-analyses found mild post-operative impairments in verbal learning and executive function in patients who underwent DBS surgery. However, studies have revealed improved working memory and psychomotor speed in the 'on' vs 'off' stimulation state. A deficit in language may be a consequence of the surgical procedure.

CONCLUSIONS

While cognitive decline has been observed in some domains, our review of the data suggests that STN DBS is a worthwhile and safe method to treat PD.

Review of the therapeutic management of Parkinson's disease. Report of a joint task force of the European Federation of Neurological Societies (EFNS) and the Movement Disorder Society-European Section (MDS-ES). Part II: late (complicated) Parkinson's disease

To provide evidence-based recommendations for the management of late (complicated) Parkinson's disease (PD), based on a review of the literature. Complicated PD refers to patients suffering from the classical motor syndrome of PD along with other motor or non-motor complications, either disease-related (e.g. freezing) or treatment-related (e.g. dyskinesias or hallucinations). MEDLINE, Cochrane Library and INAHTA database literature searches were conducted. National guidelines were requested from all EFNS societies. Non-European guidelines were searched for using MEDLINE. Part II of the guidelines deals with treatment of motor and neuropsychiatric complications and autonomic disturbances. For each topic, a list of therapeutic interventions is provided, including classification of evidence. Following this, recommendations for management are given, alongside ratings of efficacy. Classifications of evidence and ratings of efficacy are made according to EFNS guidance. In cases where there is insufficient scientific evidence, a consensus statement ('good practice point') is made.

Verbal fluency impairments among middle-aged and older outpatients with schizophrenia are characterized by deficient switching

Patients with schizophrenia demonstrate impaired verbal fluency, but no studies have examined the underlying cognitive mechanisms (e.g., clustering and switching) associated with impaired fluency among middle-aged and older, non-institutionalized patients. Using Troyer et al.'s [Troyer, A.K., Moscovitch, M., Winocur, G., 1997. Clustering and switching as two components of verbal fluency: evidence from younger and older healthy adults. Neuropsychology 11 (1), 138-146] conceptual model, we examined clustering and switching on verbal fluency tasks among 163 middle-aged and older outpatients with schizophrenia and 92 age comparable healthy comparison (HC) participants. The patients produced significantly fewer total words than HC participants on both the letter ("F", "A", "S") and Animal fluency conditions. With regard to clustering, patients were similar to HC participants on both FAS and Animal fluency tasks. However, significantly fewer switches between lexical-semantic categories were observed among patients with schizophrenia on both conditions relative to HC participants. A small, but statistically significant association was found between number of switches on the Animal fluency task and severity of negative symptoms. The absence of a difference in mean cluster size between the patient and HC groups suggests intact lexical-semantic stores among middle-aged and older outpatients with schizophrenia. Differences in switching between patients and HC participants may be driven by several cognitive impairments associated with schizophrenia. Further delineation of the cognitive mechanisms of the observed lexical-semantic switching deficits in schizophrenia should be a focus of future research.

Deep brain stimulation: neuropsychological and neuropsychiatric issues

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor, cognitive, neuropsychiatric, autonomic, and other nonmotor symptoms. The efficacy of deep brain stimulation (DBS) for the motor symptoms of advanced PD is well established. However, the effects of DBS on the cognitive and neuropsychiatric symptoms are less clear. The neuropsychiatric aspects of DBS for PD have recently been of considerable clinical and pathophysiological interest. As a companion to the preoperative and postoperative sections of the DBS consensus articles, this article reviews the published literature on the cognitive and neuropsychiatric aspects of DBS for PD. The majority of the observed neuropsychiatric symptoms are transient, treatable, and potentially preventable. Outcome studies, methodological issues, pathophysiology, and preoperative and postoperative management of the cognitive and neuropsychiatric aspects and complications of DBS for PD are discussed.

Clinical correlates and cognitive underpinnings of verbal fluency impairment after chronic subthalamic stimulation in Parkinson's disease

A decline in verbal fluency is the most consistent neuropsychological sequela of deep brain stimulation (DBS) for Parkinson's disease. We assessed clinical correlates and switching and clustering subcomponents in 26 parkinsonians undergoing subthalamic DBS. Post-surgical motor improvement was accompanied by worsening at both letter and category fluency tasks. Total number of words and switches decreased, while average cluster size was unchanged. Worsening tended to be prominent in patients with baseline poorer cognitive status and more depressed mood. Impairment of shifting suggests prefrontal dysfunction, possibly due to disruption of fronto-striatal circuits along the surgical trajectory and/or to high frequency stimulation itself.

Lack of inhibition in Parkinson's disease: evidence from a lexical decision task

Persons affected by Parkinson's disease (PD) often show an increased semantic priming effect from target words in lexical decision tasks (hyper-priming) as compared to age-matched controls. In this study, a lexical decision task was used to investigate both semantic priming (Experiment 1) and repetition priming (Experiment 2) from distractor words in PD patients and age-matched controls. With this negative priming procedure, target words in successive trials are never related, and therefore participants always have to switch between unrelated target words. Instead, it is the distractor prime word that is either related or unrelated to the subsequent target, giving the measure of priming. Results showed that PD patients demonstrated a robust effect of positive semantic priming from distractor words. Participants from the control group did not show any semantic priming effect (positive or negative) from distractors. Similarly, PD patients showed positive repetition priming from distractor words, but the control group showed significant repetition negative priming. These results support the view that the hyper-priming effect typically shown by persons with Parkinson's disease is the result of impaired inhibitory processes required to control word activation during reading.

Changes induced by levodopa and subthalamic nucleus stimulation on parkinsonian speech

Levodopa (L-dopa) and subthalamic nucleus (STN) stimulation treatments have been associated with both improvement and exacerbation of dysarthria in Parkinson's disease (PD). We report four cases illustrating variant responses of dysarthria to dopaminergic and STN stimulation therapies. Patients' motor disability and dysarthria were perceptually rated by the Unified Parkinson's Disease Rating Scale (UPDRS) in four conditions according to medication and STN stimulation. Dedicated software packages allowed acquisition and analysis of acoustic recordings. Case 1, who had a severe off period aphonia, experienced improvement of speech induced by both levodopa and STN stimulation. In Case 2, both treatments worsened speech due to the appearance of dyskinesias. Case 3 had a dysarthria exacerbation induced by STN stimulation with parameters above optimal levels, interpreted as current diffusion from the STN to corticobulbar fibers. In Case 4, dysarthria exacerbation occurred with stimulation at an electrode contact located caudally to the target, also arguing for current diffusion as a potential mechanism of speech worsening. The presented cases demonstrated variant effects in relation to L-dopa and STN stimulation on speech. It seems that motor speech subcomponents can be improved like other limb motor aspect, but that complex coordination of all speech anatomical substrates is not responsive to STN stimulation. These hypotheses may be helpful for better understanding and management of STN stimulation effects on motor speech and skeleton-motor subsystems.

Treatments for dysarthria in Parkinson's disease

Dysarthria in Parkinson's disease can be characterised by monotony of pitch and loudness, reduced stress, variable rate, imprecise consonants, and a breathy and harsh voice. Use of levodopa to replenish dopamine concentrations in the striatum seems to improve articulation, voice quality, and pitch variation, although some studies show no change in phonatory parameters. Traditional speech therapy can lead to improvement of dysarthria, and intensive programmes have had substantial beneficial effects on vocal loudness. Unilateral surgical lesions of subcortical structures are variably effective for the alleviation of dysarthria, whereas bilateral procedures typically lead to worsening of speech production. Among deep-brain stimulation procedures, only stimulation of the subthalamic nucleus improves some motor components of speech although intelligibility seems to decrease after surgery. Due to the variable treatment effects on parkinsonian speech, management of dysarthria is still challenging for the clinician and should be discussed with the patient.

Neuropsychiatric complications of medical and surgical therapies for Parkinson's disease

This review deals with the range of neuropsychiatric problems that may arise from the use of medical and surgical therapies in the treatment of Parkinson's disease. As new approaches emerge, these problems are diversifying. Well-recognized drug-related complications include hallucinations and psychosis and the so-called dopamine-dysregulation syndrome. The etiology of these problems has not been fully established and is not clearly dose related, while the management can be difficult and needs to be tailored to the individual patient. Cholinergic and dopaminergic drugs may both influence cognitive function. The development of pharmacogenetics could improve the therapeutic ratio of medical approaches to PD in the future. The literature relating to the neuropsychiatric issues complicating the surgical treatment of Parkinson's disease is more recent and frequently suffers from methodological problems, lack of a systematic approach, and adequate patient follow-up. The emergence of neuropsychiatric problems in association with surgery has shed new light upon the pathophysiological mechanisms underpinning these symptoms. Depression, hypomania, euphoria, mirth, and hypersexuality have all been described following deep brain stimulation procedures, although most studies have concentrated upon the depressive features. Anxiety has been described only rarely to date. Fortunately, permanent cognitive complications appear to be rare. The optimal management approach for surgically related neuropsychiatric problems is unknown at present. Prospective multicenter studies would contribute significantly to resolving this therapeutic uncertainty.

Verbal fluency declines after pallidotomy: an interaction between task and lesion laterality

Verbal fluency declines are commonly reported after pallidotomy in patients with Parkinson's disease. However, it is not clear whether there is an interaction between side of surgery and task format (lexical vs. semantic) or whether error rates (perseverations, intrusions, rule violations) increase after surgery. This study examined verbal fluency before and approximately 4 months after unilateral pallidotomy. The left and right pallidotomy groups were matched on key demographic, cognitive, and disease variables. Pallidotomy resulted in a decline in lexical but not semantic verbal fluency, and this decline was most evident in the left-sided surgery group. Error rates (perseverations, intrusions, and rule violations) were not affected by pallidotomy. Findings support the role of left frontal-basal ganglionic circuits in word retrieval processes and/or lexical search and access.