Neurophysiological Evidence of Compensatory Brain Mechanisms in Early-Stage Multiple Sclerosis

Relationship between event-related potentials and cognitive dysfunction in multiple sclerosis: A systematic review

OBJECTIVE

This systematic review aimed to evaluate if event-related potentials (ERPs) can be a relevant tool for cognitive dysfunction diagnosis in Multiple Sclerosis (MS).

METHODS

Four databases were consulted (PubMed, Embase, Scielo, and Web of Science). The included studies should include adults with clear MS diagnoses, independently of having cognitive complaints, and all should have been submitted to ERPs (P300, N400 or mismatch negativity (MMN)). The main outcomes evaluated were ERPs' amplitude and/or latency.

RESULTS

425 studies were obtained initially from all databases, with 26 studies fulfilling the eligibility criteria. P300 was the most used ERP (25 studies), showing a reduced amplitude or an increased latency in 84% of those. N400 was evaluated in one study, showing also abnormal results. MMN was addressed in two studies with inconsistent findings. Some studies further suggest that ERPs may show earlier abnormal results compared with neuropsychological tests.

CONCLUSIONS

Most MS patient groups revealed ERP abnormalities, suggesting that these neurophysiological tests may be a relevant and appropriate diagnostic aid method for cognitive impairment in MS.

SIGNIFICANCE

The use of ERPs in MS patients seems able to demonstrate cognitive impairment and its use should be considered as part of the regular patient evaluation.

The use of event-related potentials in the investigation of cognitive performance in people with Multiple Sclerosis: Systematic review

A biomarker of cognition in Multiple Sclerosis (MS) that is independent from the response of people with MS (PwMS) to test questions would provide a more holistic assessment of cognitive decline. One suggested method involves event-related potentials (ERPs). This systematic review tried to answer five questions about the use of ERPs in distinguishing PwMS from controls: which stimulus modality, which experimental paradigm, which electrodes, and which ERP components are most discriminatory, and whether amplitude or latency is a better measure. Our results show larger pooled effect sizes for visual stimuli than auditory stimuli, and larger pooled effect sizes for latency measurements than amplitude measurements. We observed great heterogeneity in methods and suggest that future research would benefit from more uniformity in methods and that results should be reported for the individual subtypes of PwMS. With more standardised methods, ERPs have the potential to be developed into a clinical tool in MS.

Identification and management of subclinical disease activity in early multiple sclerosis: a review

IMPORTANCE

Early treatment initiation in multiple sclerosis (MS) is crucial in preventing irreversible neurological damage and disability progression. The current assessment of disease activity relies on relapse rates and magnetic resonance imaging (MRI) lesion activity, but inclusion of other early, often "hidden," indicators of disease activity may describe a more comprehensive picture of MS.

OBSERVATIONS

Early indicators of MS disease activity other than relapses and MRI activity, such as cognitive impairment, brain atrophy, and fatigue, are not typically captured by routine disease monitoring. Furthermore, silent progression (neurological decline not clearly captured by standard methods) may occur undetected by relapse and MRI lesion activity monitoring. Consequently, patients considered to have no disease activity actually may have worsening disease, suggesting a need to revise MS management strategies with respect to timely initiation and escalation of disease-modifying therapy (DMT). Traditionally, first-line MS treatment starts with low- or moderate-efficacy therapies, before escalating to high-efficacy therapies (HETs) after evidence of breakthrough disease activity. However, multiple observational studies have shown that early initiation of HETs can prevent or reduce disability progression. Ongoing randomized clinical trials are comparing escalation and early HET approaches.

CONCLUSIONS AND RELEVANCE

There is an urgent need to reassess how MS disease activity and worsening are measured. A greater awareness of "hidden" indicators, potentially combined with biomarkers to reveal silent disease activity and neurodegeneration underlying MS, would provide a more complete picture of MS and allow for timely therapeutic intervention with HET or switching DMTs to address suboptimal treatment responses.

Disease phenotype prediction in multiple sclerosis

Progressive multiple sclerosis (PMS) is currently diagnosed retrospectively. Here, we work toward a set of biomarkers that could assist in early diagnosis of PMS. A selection of cerebrospinal fluid metabolites (n = 15) was shown to differentiate between PMS and its preceding phenotype in an independent cohort (AUC = 0.93). Complementing the classifier with conformal prediction showed that highly confident predictions could be made, and that three out of eight patients developing PMS within three years of sample collection were predicted as PMS at that time point. Finally, this methodology was applied to PMS patients as part of a clinical trial for intrathecal treatment with rituximab. The methodology showed that 68% of the patients decreased their similarity to the PMS phenotype one year after treatment. In conclusion, the inclusion of confidence predictors contributes with more information compared to traditional machine learning, and this information is relevant for disease monitoring.

Addiction as a brain disease? A meta-regression comparison of error-related brain potentials between addiction and neurological diseases

The notion that addiction is a "brain disorder" is widespread. However, there is a lack of evidence on the degree of disorder in terms of error processing in addiction. The present meta-analysis aimed at shedding light on this by comparing error-processes with populations with well-recognized brain disorders. We included 17 addiction and 32 neurological disorder studies that compared error-related negativity (ERN) or error positivity (Pe) amplitudes/latencies between experimental and healthy-control groups. Meta-regression analyses were performed for the intergroup comparison and other moderators. Both diagnoses were accompanied by a diminished ERN amplitude, although the degree of impairment was marginally larger in neurological disorders. Neurological disorders presented shorter ERN latencies than addiction when compared with controls. The two groups did not differ in Pe amplitude/latency. Except for a reduced ERN amplitude found along with aging, no other moderator contributed significantly to divergent findings about these four ERP indexes. The results support the brain disease model of addiction, while stressing the importance of quantifying the degrees of brain dysfunctions as a next step.

Neuroprotective influence of macular xanthophylls and retinal integrity on cognitive function among persons with multiple sclerosis

BACKGROUND

No studies to date have examined if macular xanthophyll accumulation and retinal integrity are independently associated with cognitive function in individuals with multiple sclerosis (MS). This study explored whether macular xanthophyll accumulation and structural morphometry in the retina were associated with behavioral performance and neuroelectric function during a computerized cognitive task among persons with MS and healthy controls (HCs).

METHODS

42 HCs and 42 individuals with MS aged 18-64 years were enrolled. Macular pigment optical density (MPOD) was measured using heterochromatic flicker photometry. Optic disc retinal nerve fiber layer (odRNFL), macular retinal nerve fiber layer, and total macular volume were assessed via optical coherence tomography. Attentional inhibition was assessed using an Eriksen flanker task while underlying neuroelectric function was recorded using event-related potentials.

RESULTS

Persons with MS had a slower reaction time, lower accuracy, and delayed P3 peak latency time during both congruent and incongruent trials compared with HCs. Within the MS group, MPOD explained variance in incongruent P3 peak latency, and odRNFL explained variance in congruent reaction time and congruent P3 peak latency.

CONCLUSIONS

Persons with MS exhibited poorer attentional inhibition and slower processing speed, yet higher MPOD and odRNFL levels were independently associated with greater attentional inhibition and faster processing speed among persons with MS. Future interventions are necessary to determine if improvements in these metrics may promote cognitive function among persons with MS.

The role of attentional control over interference in minor hallucinations in Parkinson's disease

BACKGROUND

Minor hallucinations in Parkinson's disease are associated with connectivity changes in attentional networks and increased risk of structured hallucinations. However, the clinical translation of these abnormalities in attention processes is not well-defined, and commonly used neuropsychological tests are not able to detect significant deficits in Parkinson's disease patients with isolated minor hallucinations.

OBJECTIVES

To analyze the behavioral and electrophysiological correlates of minor hallucinations in Parkinson's disease during an attentional task assessing response inhibition and interference control.

METHODS

Fifty-five non-demented Parkinson's disease patients with (PD-mH; n = 27) and without minor hallucinations (PD-NH; n = 28) were included in the analysis. An Ericksen flanker task was performed to compare the effect of presenting congruent and incongruent stimuli on accuracy, reaction times and stimulus-locked event-related potentials morphology.

RESULTS

Although both groups showed equivalent performance in a standard neuropsychological assessment, in the flanker task accuracy rates were lower in the PD-mH group in incongruent trials (p = 0.005). In the event-related potentials, PD-mH patients showed increased amplitude of the N2 at Fz [t(53); p < 0.05] and decreased amplitude of the P300 at Pz [t(53); p < 0.05] for the incongruent trials.

CONCLUSIONS

Parkinson's disease patients with isolated minor hallucinations were more susceptible to interference mediated by irrelevant stimuli and had less cognitive control for suppressing these interferences. The failure of these systems could precipitate the intrusion and overrepresentation of peripheral irrelevant stimuli perceived as minor hallucinations. The Ericksen flanker task could be used as a sensitive clinical marker of the attentional defects leading to hallucinations in Parkinson's disease.

Cerebellar Contributions to Motor and Cognitive Control in Multiple Sclerosis✰✰✰

OBJECTIVE

To evaluate relationships between specific cerebellar regions and common clinical measures of motor and cognitive function in persons with multiple sclerosis (PwMS).

DESIGN

Cross-sectional.

SETTING

Laboratory.

PARTICIPANTS

Twenty-nine PwMS and 28 age- and sex-matched controls without multiple sclerosis (MS) (N=57).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Both diffusion and lobule magnetic resonance imaging analyses and common clinical measures of motor and cognitive function were used to examine structure-function relationships in the cerebellum.

RESULTS

PwMS demonstrate significantly worse motor and cognitive function than controls, including weaker strength, slower walking, and poorer performance on the Symbol Digit Modalities Test, but demonstrate no differences in cerebellar volume. However, PwMS demonstrate significantly worse diffusivity (mean diffusivity: P=.0003; axial diffusivity: P=.0015; radial diffusivity: P=.0005; fractional anisotropy: P=.016) of the superior cerebellar peduncle, the primary output of the cerebellum. Increased volume of the motor lobules (I-V, VIII) was significantly related to better motor (P<.022) and cognitive (P=.046) performance, and increased volume of the cognitive lobules (VI-VII) was also related to better motor (P<.032) and cognitive (P=.008) performance, supporting the role of the cerebellum in both motor and cognitive functioning.

CONCLUSIONS

These data highlight the contributions of the cerebellum to both motor and cognitive function in PwMS. Using novel neuroimaging techniques to examine structure-function relationships in PwMS improves our understanding of individualized differences in this heterogeneous group and may provide an avenue for targeted, individualized rehabilitation aimed at improving cerebellar dysfunction in MS.

Multimodal Evoked Potentials as Potential Biomarkers of Disease Activity in Patients With Clinically Isolated Syndrome

Objective

There is an ongoing search for markers useful in monitoring and predicting disease activity at the early stage of multiple sclerosis (MS). The goals of this study were to prospectively evaluate the changes in parameters of multimodal evoked potentials (EP) and cognition within a 3-year follow-up period in patients with clinically isolated syndrome (CIS), and to assess the prognostic value of baseline findings with regard to the disease outcomes.

Methods

In 29 patients (20 women, nine men, mean age 31.1) multimodal (visual, brainstem auditory, somatosensory, event-related) EP and neuropsychological tests (NT) were performed at baseline (T0) and after 1 (T1) and 3 (T3) years. Their results were compared longitudinally between baseline, T1, and T3. Baseline results confirmed conversion of CIS into multiple sclerosis (MS) and disability level at T1 and T3 using multiple comparisons and a logistic regression model.

Results

Apart from mean N13/P16 SEP (somatosensory evoked potentials) amplitude (lower at T1 and T3 than at baseline (T0 1.02 ± 0.37 μV, T1 0.90 ± 0.26 μV, T3 0.74 ± 0.32 μV, p < 0.05 for both comparisons), no significant changes of EP or NT parameters were found in longitudinal assessment. Baseline P300 Pz latency was longer for the patients with MS than for those with CIS at T1 (352.69 vs. 325.56 ms). No predictive value was shown for any of the analyzed baseline variables with regard to conversion from CIS into MS.

Significance

Baseline ERP abnormalities were associated with their short-term conversion into MS. ERP are worth considering in multimodal EP evaluation at the early stage of MS.

Cognitive screening in HTLV-1-infected people using a self-perceived memory score and auditory P300

The HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is the most common neurological manifestation associated with human T-cell lymphotropic virus type-1 (HTLV-1) infection. Although cognitive impairment has been highlighted in the spectrum of HTLV-1 neurological manifestations, it may go unnoticed in those who do not spontaneously report it. We aimed at evaluating the applicability of a self-perceived memory score (SMS) and the cognitive event-related potential (P300) for early detection of cognitive impairment in HTLV-1-infected people. The SMS was measured by a 0-10 point numeric scale combined with a sad-happy face rating scale. The higher the number, the better was the SMS. The P300 was obtained through an oddball paradigm with a mental counting task. The participants were 15 (21.4%) individuals with HAM/TSP, 20 (28.6%) HTLV-1 asymptomatic carriers, and 35 (50%) seronegative controls. We found that SMS (p < 0.001) and P300 latency (p < 0.001) got progressively worse from the seronegative controls to the asymptomatic carriers and then to the HAM/TSP. The results that indicated cognitive impairment were SMS < 7.2 points and P300 latency > 369.0 ms. The HAM/TSP group showed the highest prevalence of altered P300 (80%) and SMS (87%). Interestingly, the asymptomatic group also presented significantly higher prevalence of altered SMS (60%) and P300 (35%) when compared to controls (< 10%). The frequency of cognitive impairment was 16 times higher in the HTLV-1 asymptomatic group and 69 times higher in the HAM/TSP group when compared to controls. The use of SMS in the medical consultation was a useful and easy-to-apply method to screen HTLV-1-infected subjects for everyday memory complaints.

Linking immune-mediated damage to neurodegeneration in multiple sclerosis: could network-based MRI help?

Inflammatory demyelination characterizes the initial stages of multiple sclerosis, while progressive axonal and neuronal loss are coexisting and significantly contribute to the long-term physical and cognitive impairment. There is an unmet need for a conceptual shift from a dualistic view of multiple sclerosis pathology, involving either inflammatory demyelination or neurodegeneration, to integrative dynamic models of brain reorganization, where, glia-neuron interactions, synaptic alterations and grey matter pathology are longitudinally envisaged at the whole-brain level. Functional and structural MRI can delineate network hallmarks for relapses, remissions or disease progression, which can be linked to the pathophysiology behind inflammatory attacks, repair and neurodegeneration. Here, we aim to unify recent findings of grey matter circuits dynamics in multiple sclerosis within the framework of molecular and pathophysiological hallmarks combined with disease-related network reorganization, while highlighting advances from animal models (in vivo and ex vivo) and human clinical data (imaging and histological). We propose that MRI-based brain networks characterization is essential for better delineating ongoing pathology and elaboration of particular mechanisms that may serve for accurate modelling and prediction of disease courses throughout disease stages.

Effects of a Green Oat Herb Extract on Cognitive Performance and Neurophysiological Activity: A Randomized Double-Blind Placebo-Controlled Study

Green oat extracts have been used for centuries in traditional medicine in view of their supposed beneficial effects on cognition and mood. Recently, a specific green oat formulation (Neuravena^®) showed to have significant bioactive compounds potentially associated with the enhancement of processing speed, working memory and attention. The main aim of the current study was to compare the potential effect of acute administration of 800 mg of Neuravena^® with placebo on a set of neurophysiological correlates of processing speed, attention, performance-monitoring and inhibitory control. Twenty healthy participants were randomized to receive either Neuravena^® or placebo. Electroencephalographic (EEG) signal acquisition was obtained while participants carried out the modified Eriksen flanker and oddball tasks. Both groups were compared on measures of behavioral task performance, and a set of event-related potentials (ERPs) components related to performance monitoring (the error-related negativity; ERN and the N2), target detection, and attention (P3a/P3b). Following active-intervention N2, ERN, and P3a/P3b were significantly reduced and performance was faster, with no loss of accuracy. Conversely, no neurophysiological differences were found in the placebo group before and after treatment and performance worsened significantly in terms of reaction time and accuracy. Acute administration of 800 mg of Neuravena^® appears to enhance the optimization of neural resources and positively influences cognitive performance in tasks associated with executive functions, processing speed and attention. Moreover, Neuravena^® prevents the deleterious effects of tiredness during task performance.

New insights into neural networks of error monitoring and clinical implications: a systematic review of ERP studies in neurological diseases

Error monitoring allows for the efficient performance of goal-directed behaviors and successful learning. Furthermore, error monitoring as a metacognitive ability may play a crucial role for neuropsychological interventions, such as rehabilitation. In the past decades, research has suggested two electrophysiological markers for error monitoring: the error-related negativity (ERN) and the error positivity (Pe), thought to reflect, respectively, error detection and error awareness. Studies on several neurological diseases have investigated the alteration of the ERN and the Pe, but these findings have not been summarized. Accordingly, a systematic review was conducted to understand what neurological conditions present alterations of error monitoring event-related potentials and their relation with clinical measures. Overall, ERN tended to be reduced in most neurological conditions while results related to Pe integrity are less clear. ERN and Pe were found to be associated with several measures of clinical severity. Additionally, we explored the contribution of different brain structures to neural networks underlying error monitoring, further elaborating on the domain-specificity of error processing and clinical implications of findings. In conclusion, electrophysiological signatures of error monitoring could be reliable measures of neurological dysfunction and a robust tool in neuropsychological rehabilitation.

Deficits in Early Sensory and Cognitive Processing Are Related to Phase and Nonphase EEG Activity in Multiple Sclerosis Patients

Currently, there is scarce knowledge about the relation between spectral bands modulations and the basis of cognitive impairment in multiple sclerosis (MS). In this sense, analyzing the evoked or phase activity can confirm results from traditional event-related potential (ERP) studies. However, studying the induced or nonphase activity may be necessary to elucidate hidden compensatory or affected cognitive mechanisms. In this study, 30 remitting-relapsing multiple sclerosis patients and 30 healthy controls (HCs) matched in sociodemographic variables performed a visual oddball task. The main goal was to analyze phase and nonphase alpha and gamma bands by applying temporal spectral evolution (TSE) and its potential relation with cognitive impairment in these patients. The behavioural results showed slower reaction time and poorer accuracy in MS patients compared to controls. In contrast, the time-frequency analysis of electroencephalography (EEG) revealed a delay in latency and lower amplitude in MS patients in evoked and induced alpha compared to controls. With respect to the gamma band, there were no differences between the groups. In summary, MS patients showed deficits in early sensorial (evoked alpha activity) and cognitive processing (induced alpha activity in longer latencies), whereas the induced gamma band supported the hypothesis of its role in translation of attentional focus (induced activity) and did not show strong activity in this paradigm (visual oddball).

Myelin and axon pathology in multiple sclerosis assessed by myelin water and multi-shell diffusion imaging

Damage to the myelin sheath and the neuroaxonal unit is a cardinal feature of multiple sclerosis; however, a detailed characterization of the interaction between myelin and axon damage in vivo remains challenging. We applied myelin water and multi-shell diffusion imaging to quantify the relative damage to myelin and axons (i) among different lesion types; (ii) in normal-appearing tissue; and (iii) across multiple sclerosis clinical subtypes and healthy controls. We also assessed the relation of focal myelin/axon damage with disability and serum neurofilament light chain as a global biological measure of neuroaxonal damage. Ninety-one multiple sclerosis patients (62 relapsing-remitting, 29 progressive) and 72 healthy controls were enrolled in the study. Differences in myelin water fraction and neurite density index were substantial when lesions were compared to healthy control subjects and normal-appearing multiple sclerosis tissue: both white matter and cortical lesions exhibited a decreased myelin water fraction and neurite density index compared with healthy (P < 0.0001) and peri-plaque white matter (P < 0.0001). Periventricular lesions showed decreased myelin water fraction and neurite density index compared with lesions in the juxtacortical region (P < 0.0001 and P < 0.05). Similarly, lesions with paramagnetic rims showed decreased myelin water fraction and neurite density index relative to lesions without a rim (P < 0.0001). Also, in 75% of white matter lesions, the reduction in neurite density index was higher than the reduction in the myelin water fraction. Besides, normal-appearing white and grey matter revealed diffuse reduction of myelin water fraction and neurite density index in multiple sclerosis compared to healthy controls (P < 0.01). Further, a more extensive reduction in myelin water fraction and neurite density index in normal-appearing cortex was observed in progressive versus relapsing-remitting participants. Neurite density index in white matter lesions correlated with disability in patients with clinical deficits (P < 0.01, beta = -10.00); and neurite density index and myelin water fraction in white matter lesions were associated to serum neurofilament light chain in the entire patient cohort (P < 0.01, beta = -3.60 and P < 0.01, beta = 0.13, respectively). These findings suggest that (i) myelin and axon pathology in multiple sclerosis is extensive in both lesions and normal-appearing tissue; (ii) particular types of lesions exhibit more damage to myelin and axons than others; (iii) progressive patients differ from relapsing-remitting patients because of more extensive axon/myelin damage in the cortex; and (iv) myelin and axon pathology in lesions is related to disability in patients with clinical deficits and global measures of neuroaxonal damage.

Identifying Early Neuropsychological Indicators of Cognitive Involvement in Multiple Sclerosis

Multiple sclerosis (MS) is a debilitating disease of the central nervous system that is most commonly seen in early to middle adulthood, although it can be diagnosed during childhood or later in life. While cognitive impairment can become more prevalent and severe as the disease progresses, signs of cognitive involvement can be apparent in the early stages of the disease. In this review, we discuss the prevalence and types of cognitive impairment seen in early MS, including the specific measures used to identify them, as well as the challenges in characterizing their frequency and progression. In addition to examining the progression of early cognitive involvement over time, we explore the clinical factors associated with early cognitive involvement, including demographics, level of physical disability, disease modifying therapy use, vocational status, and psychological and physical symptoms. Given the prevalence and functional impact these impairments can have for persons with MS, considerations for clinicians are provided, such as the role of early cognitive screenings and the importance of comprehensive neuropsychological assessments.

Doing it Wrong: A Systematic Review on Electrocortical and Behavioral Correlates of Error Monitoring in Patients with Neurological Disorders

Detecting errors in one's own and other's actions is a crucial ability for learning and adapting behavior to everchanging, highly volatile environments. Studies in healthy people demonstrate that monitoring errors in one's own and others' actions are underpinned by specific neural systems that are dysfunctional in a variety of neurological disorders. In this review, we first briefly discuss the main findings concerning error detection and error awareness in healthy subjects, the current theoretical models, and the tasks usually applied to investigate these processes. Then, we report a systematic search for evidence of dysfunctional error monitoring among neurological populations (basal ganglia, neurodegenerative, white-matter diseases and acquired brain injury). In particular, we examine electrophysiological and behavioral evidence for specific alterations of error processing in neurological disorders. Error-related negativity (ERN) amplitude were reduced in most (although not all) neurological patient groups, whereas Positivity Error (Pe) amplitude appeared not to be affected in most patient groups. Also theta activity was reduced in some neurological groups, but consistent evidence on the oscillatory activity has not been provided thus far. Behaviorally, we did not observe relevant patterns of pronounced dysfunctional (post-) error processing. Finally, we discuss limitations of the existing literature, conclusive points, open questions and new possible methodological approaches for clinical studies.

Distributed causality in resting-state network connectivity in the acute and remitting phases of RRMS

BACKGROUND

Although previous studies have shown that intra-network abnormalities in brain functional networks are correlated with clinical/cognitive impairment in multiple sclerosis (MS), there is little information regarding the pattern of causal interactions among cognition-related resting-state networks (RSNs) in different disease stages of relapsing-remitting MS (RRMS) patients. We hypothesized that abnormalities of causal interactions among RSNs occurred in RRMS patients in the acute and remitting phases.

METHODS

Seventeen patients in the acute phases of RRMS, 24 patients in the remitting phases of RRMS, and 23 appropriately matched healthy controls participated in this study. First, we used group independent component analysis to extract the time courses of the spatially independent components from all the subjects. Then, the Granger causality analysis was used to investigate the causal relationships among RSNs in the spectral domain and to identify correlations with clinical indices.

RESULTS

Compared with the patients in the acute phase of RRMS, patients in the remitting phase of RRMS showed a significantly lower expanded disability status scale, modified fatigue impact scale scores, and significantly higher paced auditory serial addition test (PASAT) scores. Compared with healthy subjects, during the acute phase, RRMS patients had significantly increased driving connectivity from the right executive control network (rECN) to the anterior salience network (aSN), and the causal coefficient was negatively correlated with the PASAT score. During the remitting phase, RRMS patients had significantly increased driving connectivity from the rECN to the aSN and from the rECN to the visuospatial network.

CONCLUSIONS

Together with the disease duration (mean disease duration < 5 years) and relatively better clinical scores than those in the acute phase, abnormal connections, such as the information flow from the rECN to the aSN and the rECN to the visuospatial network, might provide adaptive compensation in the remitting phase of RRMS.

Time matters: Early-phase multiple sclerosis is accompanied by considerable impairments across multiple domains

Impairments across multiple domains are a disabling consequence of multiple sclerosis (MS). Originating from preventive medical strategies, the “time matters”-perspective has become a focal point when treating MS. In particular, early detection of physical and cognitive deficits, along with deficits in patient-reported outcomes seems crucial to further optimize both pharmacological and non-pharmacological MS treatment strategies. Therefore, this topical review investigates the level of impairments across multiple domains (physical function, cognitive function, and patient-reported outcomes) in the early stage of MS (⩽5 years since diagnosis, including clinically isolated syndrome (CIS)), when compared to matched healthy controls. Even at early disease stages, studies show impairments corresponding to 8%–34% and small-to-large numerical effect sizes (0.35–2.85) in MS/CIS patients across domains. This evidence call for early screening programs along with early interventions targeting the multiple impaired domains. This further highlights the importance of preventive initiatives preserving and/or restoring physical and cognitive reserve capacity if possible.

The Effects of Cognitive Training on Brain Network Activity and Connectivity in Aging and Neurodegenerative Diseases: a Systematic Review

Cognitive training (CT) is an increasingly popular, non-pharmacological intervention for improving cognitive functioning in neurodegenerative diseases and healthy aging. Although meta-analyses support the efficacy of CT in improving cognitive functioning, the neural mechanisms underlying the effects of CT are still unclear. We performed a systematic review of literature in the PubMed, Embase and PsycINFO databases on controlled CT trials (N > 20) in aging and neurodegenerative diseases with pre- and post-training functional MRI outcomes up to November 23rd 2018 (PROSPERO registration number CRD42019103662). Twenty articles were eligible for our systematic review. We distinguished between multi-domain and single-domain CT. CT induced both increases and decreases in task-related functional activation, possibly indicative of an inverted U-shaped curve association between regional brain activity and task performance. Functional connectivity within ‘cognitive’ brain networks was consistently reported to increase after CT while a minority of studies additionally reported increased segregation of frontoparietal and default mode brain networks. Although we acknowledge the large heterogeneity in type of CT, imaging methodology, in-scanner task paradigm and analysis methods between studies, we propose a working model of the effects of CT on brain activity and connectivity in the context of current knowledge on compensatory mechanisms that are associated with aging and neurodegenerative diseases.

Resting-state functional connectivity of anterior and posterior cerebellar lobes is altered in multiple sclerosis

BACKGROUND

Damage to the cerebellar sensorimotor and cognitive domains may underlie physical and cognitive disability.

OBJECTIVE

To investigate resting-state functional connectivity (FC) of sensorimotor and cognitive cerebellum, and clinical correlates in multiple sclerosis (MS).

METHODS

A total of 119 patients with MS and 42 healthy subjects underwent multimodal 3T-magnetic resonance imaging (MRI). Patients were evaluated using the Expanded Disability Status Scale and Multiple Sclerosis Functional Composite Scale. After parcellation of sensorimotor (lobules I-V + VIII) and cognitive cerebellum (lobules VI, VII, IX, X), we calculated cerebellar resting-state FC using a seed-based approach.

RESULTS

In patients with MS, the sensorimotor cerebellum showed increased FC mainly with cerebellar, thalamic, and cortical (frontal, parietal, temporal) areas and decreased FC with insular areas; the cognitive cerebellum showed increased FC mainly with thalamic and cortical (temporal-occipital) areas, and decreased FC with frontal-insular areas. Both sensorimotor and cognitive cerebellar FC negatively correlated with disability, and positively with cognitive scores. Cerebellar structural damage only partially influenced results.

CONCLUSION

The two neocerebellar circuits showed altered FC with subcortical and cortical areas. The association between increased sensorimotor and cognitive cerebellar FC and low levels of physical and cognitive disability suggests that altered FC might modulate the effects of cerebellar structural damage on clinical condition.

Mobile Brain/Body Imaging of cognitive-motor impairment in multiple sclerosis: Deriving EEG-based neuro-markers during a dual-task walking study

OBJECTIVE

Individuals with a diagnosis of multiple sclerosis (MS) often present with cognitive and motor deficits, and thus the ability to perform tasks that rely on both domains may be particularly impaired. Yet, dual-task walking studies yield mixed results. Individual variance in the ability to cope with brain insult and mobilize additional brain resources may contribute to mixed findings.

METHODS

To test this hypothesis, we acquired event-related potentials (ERP) in individuals with MS and healthy controls (HCs) performing a Go/NoGo task while sitting (i.e., single task) or walking (i.e., dual-task) and looked at the relationship between task related modulation of the brain response and performance.

RESULTS

On the Go/NoGo task the MS group showed dual-task costs when walking, whereas HCs showed a dual-task benefit. Further, whereas the HC group showed modulation of the brain response as a function of task load, this was not the case in the MS group. Analysis for the pooled sample revealed a positive correlation between load-related ERP effects and dual-task performance.

CONCLUSIONS

These data suggest a neurophysiological marker of cognitive-motor dysfunction in MS.

SIGNIFICANCE

Understanding neural processes underlying dual-task walking will help identify objective brain measurements of real-world issues and may improve assessment of MS.

A focus on secondary progressive multiple sclerosis (SPMS): challenges in diagnosis and definition

Secondary progressive multiple sclerosis (SPMS) is the second most common form of multiple sclerosis (MS). One in two relapse remitting multiple sclerosis (RRMS) patients will develop SPMS within 15 years and up to two-thirds after 30 years, leading to a progressive decrease of neurological function and limitation of daily activities. Nevertheless, the SPMS diagnosis is often established retrospectively and delayed up to 3 years due to several patient- and clinician-related factors. Definitive clinical diagnostic criteria are lacking and research is currently ongoing to identify imaging and biochemical biomarkers. As new therapies are introduced, early SPMS diagnosis may represent a window of opportunity for intervention. New approaches, endpoints or technologies could help physicians establishing a diagnosis. Here, we review SPMS in relation to its diagnostic and definition challenges and current screening techniques and tools.

A focus on secondary progressive multiple sclerosis (SPMS): challenges in diagnosis and definition

Secondary progressive multiple sclerosis (SPMS) is the second most common form of multiple sclerosis (MS). One in two relapse remitting multiple sclerosis (RRMS) patients will develop SPMS within 15 years and up to two-thirds after 30 years, leading to a progressive decrease of neurological function and limitation of daily activities. Nevertheless, the SPMS diagnosis is often established retrospectively and delayed up to 3 years due to several patient- and clinician-related factors. Definitive clinical diagnostic criteria are lacking and research is currently ongoing to identify imaging and biochemical biomarkers. As new therapies are introduced, early SPMS diagnosis may represent a window of opportunity for intervention. New approaches, endpoints or technologies could help physicians establishing a diagnosis. Here, we review SPMS in relation to its diagnostic and definition challenges and current screening techniques and tools.

Characterization of inhibitory failure in Multiple Sclerosis: Evidence of impaired conflict resolution

INTRODUCTION

Inhibitory control deficits are frequently reported in Multiple Sclerosis (MS), although it is unclear whether these deficits represent a global or process-specific failure. Notably, most models of inhibitory control recognize at least two dissociable processes, the most consistent being: (a) the inhibition of a dominant response: response suppression, and (b) the inhibition of a dominant response and initiation of a nondominant response: executive control. This study aimed to ascertain the processes underlying inhibitory failure in MS.

METHOD

Twenty-three MS patients and 25 healthy controls completed a battery of commonly used inhibitory tasks, with measures from each task entered into a principal components analysis with orthogonal (varimax) rotation.

RESULTS

As anticipated, two components emerged, with tasks evaluating response suppression (stop signal, go/no go) loading on a common component, and tasks evaluating executive control (Stroop, antisaccade, endogenously-cued saccade) loading on a separate common component. Composite scores were generated for each component and compared between groups. Unlike response suppression scores, executive control scores were significantly poorer for MS patients.

CONCLUSIONS

Inhibitory control deficits in MS may reflect poor resolution in the context of competing processes, rather than difficulty in preventing the execution of an inappropriate response.

Functional Connectivity Alterations Reveal Complex Mechanisms Based on Clinical and Radiological Status in Mild Relapsing Remitting Multiple Sclerosis

Resting state functional MRI (rs-fMRI) has provided important insights into functional reorganization in subjects with Multiple Sclerosis (MS) at different stage of disease. In this cross-sectional study we first assessed, by means of rs-fMRI, the impact of overall T2 lesion load (T2LL) and MS severity score (MSSS) on resting state networks (RSNs) in 62 relapsing remitting MS (RRMS) patients with mild disability (MSSS < 3). Independent Component Analysis (ICA) followed by dual regression analysis confirmed functional connectivity (FC) alterations of many RSNs in RRMS subjects compared to healthy controls. The anterior default mode network (DMNa) and the superior precuneus network (PNsup) showed the largest areas of decreased FC, while the sensory motor networks area M1 (SMNm1) and the medial visual network (MVN) showed the largest areas of increased FC. In order to better understand the nature of these alterations as well as the mechanisms of functional alterations in MS we proposed a method, based on linear regression, that takes into account FC changes and their correlation with T2LL and MSSS. Depending on the sign of the correlation between FC and T2LL, and furthermore the sign of the correlation with MSSS, we suggested the following possible underlying mechanisms to interpret altered FC: (1) FC reduction driven by MS lesions, (2) "true" functional compensatory mechanism, (3a) functional compensation attempt, (3b) "false" functional compensation, (4a) neurodegeneration, (4b) pre-symptomatic condition (damage precedes MS clinical manifestation). Our data shows areas satisfying 4 of these 6 conditions (i.e., 1,2,3b,4b), supporting the suggestion that increased FC has a complex nature that may exceed the simplistic assumption of an underlying compensatory mechanism attempting to limit the brain damage caused by MS progression. Exploring differences between RRMS subjects with short disease duration (MS_short) and RRMS with similar disability but longer disease duration (MS_long), we found that MS_short and MS_long were characterized by clearly distinct pattern of FC, involving predominantly sensory and cognitive networks respectively. Overall, these results suggest that the analysis of FC alterations in multiple large-scale networks in relation to radiological (T2LL) and clinical (MSSS, disease duration) status may provide new insights into the pathophysiology of relapse onset MS evolution.

Machine Learning EEG to Predict Cognitive Functioning and Processing Speed Over a 2-Year Period in Multiple Sclerosis Patients and Controls

Event-related potentials (ERPs) show promise to be objective indicators of cognitive functioning. The aim of the study was to examine if ERPs recorded during an oddball task would predict cognitive functioning and information processing speed in Multiple Sclerosis (MS) patients and controls at the individual level. Seventy-eight participants (35 MS patients, 43 healthy age-matched controls) completed visual and auditory 2- and 3-stimulus oddball tasks with 128-channel EEG, and a neuropsychological battery, at baseline (month 0) and at Months 13 and 26. ERPs from 0 to 700 ms and across the whole scalp were transformed into 1728 individual spatio-temporal datapoints per participant. A machine learning method that included penalized linear regression used the entire spatio-temporal ERP to predict composite scores of both cognitive functioning and processing speed at baseline (month 0), and months 13 and 26. The results showed ERPs during the visual oddball tasks could predict cognitive functioning and information processing speed at baseline and a year later in a sample of MS patients and healthy controls. In contrast, ERPs during auditory tasks were not predictive of cognitive performance. These objective neurophysiological indicators of cognitive functioning and processing speed, and machine learning methods that can interrogate high-dimensional data, show promise in outcome prediction.

Early cognitive impairment along with decreased stress-induced BDNF in male and female patients with newly diagnosed multiple sclerosis

The aim of this study was to evaluate neuroendocrine activation during stress in patients with recently diagnosed multiple sclerosis before starting the immunomodulatory therapy (EDSS score≤2.0). We verified the hypothesis that certain cognitive and affective dysfunction is present already at this early stage of the disease. The sample consisted of 38 subjects, which involved patients who were recently diagnosed multiple sclerosis and age- and sex-matched healthy volunteers. Stroop test served as mental stress model enabling measurement of cognitive performance. Present results showed increased state anxiety, depression scores and poorer performance in the Stroop test in the group of patients compared to healthy subjects. The cognitive dysfunction was particularly evident in male patients with simultaneously decreased concentrations of the brain-derived neurotrophic factor (BDNF) in plasma. The patients at this stage of the disease have not yet developed the hyperactivity of the hypothalamic-pituitary-adrenocortical axis. They showed normal levels of plasma copeptin and reduced aldosterone response to mental stress test in women only. Concentrations of plasma copeptin were higher in men compared to women. Very early stages of multiple sclerosis are accompanied by disturbances in psychological well-being, mild cognitive dysfunction and decreased plasma concentrations of BDNF, particularly in male patients.