The symbol digit modalities test and the paced auditory serial addition test involve more than processing speed

Cognitive function in physically healthy, unmedicated individuals with major depression: Relationship with depressive symptoms and antidepressant response

We studied cognitive dysfunction in Major Depressive Disorder (MDD) in a sample of healthy, unmedicated individuals without comorbidities. Additionally, we studied the association of cognitive function with response to selective serotonin reuptake inhibitors (SSRIs). Our sample consisted of 113 adult MDD participants and 88 matched healthy controls (HC). Sixty-nine of the MDD participants completed 8 weeks of SSRI treatment. All participants completed a cognitive battery assessing processing speed, executive function, and learning and memory at baseline. This was repeated at week 8 for MDD participants. MDD "Responders" were defined as having ≥50 % improvement on the Hamilton Depression Rating Scale score at week 8 compared to baseline. At baseline, MDD participants performed significantly worse than HC participants on the Symbol Digit Modalities Test (SDMT) (p < .001), Stroop color naming (p = .005) and color-word naming (p = .047), and Brief Visuospatial Memory Test-Revised (BVMT) total recall (p = .02), delayed recall (p < .001), and percent retention (p = .01). MDD participants improved significantly on 6 of the cognitive assessments over 8 weeks. However, there were no significant baseline differences between Responders and Non-responders. SSRI Response was associated with improvement only in the HVLT total recall (p = .02). Our results suggest: 1) a differentiated pattern of cognitive dysfunction exists in healthy, unmedicated MDD compared to HCs; 2) baseline cognition does not delineate an SSRI-responsive/-nonresponsive subgroup, and 3) SSRI response is not associated with broad cognitive improvement after 8 weeks when compared to Non-responders, emphasizing unmet therapeutic challenges.

Trait fatigue impacts Symbol Digit Modalities Test (SDMT) performance in multiple sclerosis: The role of working memory

BACKGROUND

Cognitive impairment and fatigue are two prevalent symptoms of multiple sclerosis (MS). Fatigue is often thought to be associated with slower processing speed. The Symbol Digit Modalities Test (SDMT) is a widely used assessment of processing speed in MS, but it has also been shown to tap into working memory as well. Investigation into fatigue's influence on SDMT performance in MS and potential mechanisms for this relationship are lacking. The present study examined the effect of trait fatigue on SDMT performance and its associated mechanisms in MS and healthy control (HC) participants. Working memory performance was specifically examined as a potential mechanism, given its frequent association with processing speed in MS.

METHODS

In a secondary data analysis, performance on the SDMT and other neuropsychological assessments, as well as self-reported trait fatigue, were examined in 80 MS and 45 HC participants. Trait fatigue was measured via self-report on the Modified Fatigue Impact Scale (MFIS).

RESULTS

Higher MFIS ratings were significantly associated with worse SDMT performance in MS (r = -0.33, p = .002), but not HC (r= 0.06, p = .71), participants. A mediation analysis further revealed that for MS participants, working memory performance (WAIS-IV Digit Span Backward condition) partially mediated the relationship between trait fatigue and SDMT performance. Higher MFIS scores significantly predicted lower Digit Span Backward scores (b = -0.04, 95 % CI: [-0.08, -0.002], p = .04], which in turn, significantly predicted lower SDMT response accuracy (b = 0.23, 95 % CI: [0.10, 0.35], p = .001). No such relationship was observed in HC participants.

CONCLUSIONS

Elevated trait fatigue may reduce SDMT performance via its negative impact on working memory performance in people with MS. Future research should focus on additional factors that may also contribute to this relationship.

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.

Oculomotor analysis to assess brain health: preliminary findings from a longitudinal study of multiple sclerosis using novel tablet-based eye-tracking software

A growing body of evidence supports the link between eye movement anomalies and brain health. Indeed, the oculomotor system is composed of a diverse network of cortical and subcortical structures and circuits that are susceptible to a variety of degenerative processes. Here we show preliminary findings from the baseline measurements of an ongoing longitudinal cohort study in MS participants, designed to determine if disease and cognitive status can be estimated and tracked with high accuracy based on eye movement parameters alone. Using a novel gaze-tracking technology that can reliably and accurately track eye movements with good precision without the need for infrared cameras, using only an iPad Pro embedded camera, we show in this cross-sectional study that several eye movement parameters significantly correlated with clinical outcome measures of interest. Eye movement parameters were extracted from fixation, pro-saccade, anti-saccade, and smooth pursuit visual tasks, whereas the clinical outcome measures were the scores of several disease assessment tools and standard cognitive tests such as the Expanded Disability Status Scale (EDSS), Brief International Cognitive Assessment for MS (BICAMS), the Multiple Sclerosis Functional Composite (MSFC) and the Symbol Digit Modalities Test (SDMT). Furthermore, partial least squares regression analyses show that a small set of oculomotor parameters can explain up to 84% of the variance of the clinical outcome measures. Taken together, these findings not only replicate previously known associations between eye movement parameters and clinical scores, this time using a novel mobile-based technology, but also the notion that interrogating the oculomotor system with a novel eye-tracking technology can inform us of disease severity, as well as the cognitive status of MS participants.