Cognitive mediated eye movements during the SDMT reveal the challenges with processing speed faced by people with MS

Bennis Pavisian,Viral P Patel,Anthony Feinstein

doi:10.1186/s12883-019-1543-8

Bennis Pavisian, Viral P Patel + Show 1 more

Open Access

https://doi.org/10.1186/s12883-019-1543-8

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Abstract

BackgroundThe Symbol Digit Modalities Test (SDMT) is regarded as the cognitive test of choice for people with MS (pwMS). While deficits are linked to impaired processing speed, the mechanisms by which they arise are unclear. Cognitive-mediated eye movements offer one putative explanation. The objective of this study was to determine the association between eye movements and performance on the SDMT.MethodsThirty-three people with confirmed MS and 25 matched healthy control subjects (HC) were administered the oral SDMT while eye movements were recorded.ResultsMean SDMT scores were significantly lower in pwMS (p < 0.038). Shorter mean saccade distance in the key area (p = 0.007), more visits to the key area per response (p = 0.014), and more total number of fixations in the test area (p = 0.045) differentiated pwMS from HCs. A hierarchical regression analysis revealed that the number of visits to the key area per response (p < 0.001; ΔR2 = 0.549) and total number of fixations in the test area (p < 0.001; ΔR2 = 0.782) were the most robust predictors of SDMT scores.ConclusionCognitive-mediated eye movements help elucidate the processing speed challenges confronted by people with MS. Mechanistic insights such as these can potentially help inform new cognitive rehabilitation strategies.

Highlights

The Symbol Digit Modalities Test (SDMT) is regarded as the cognitive test of choice for people with MS
Seven (21.21%) MS participants were impaired on the SDMT, as defined by a score of 1.5 standard deviations below the mean performance of the healthy control subjects
Our study confirmed that people with MS perform slower on the SDMT than healthy individuals and revealed that eye movement metrics are predictive of performance

Summary

Introduction

The Symbol Digit Modalities Test (SDMT) is regarded as the cognitive test of choice for people with MS (pwMS). While there is a substantial literature devoted to eye movement abnormalities in general in pwMS, [13,14,15,16] and links established with cognitive dysfunction, [17, 18] reported associations with impairments on the SDMT are equivocal [19,20,21]. Of note is that none of the three SDMT studies monitored eye movements during the actual performance of the task, rather, assocations or a lack thereof were reported between SDMT performance on the one hand, and separate measurements of eye movement, on the other Allied to this observation is another, namely that the majority of MS-SDMT studies do not take visual abnormalities into account in their methodology and interpreation of results [10]. Given this relative dearth of information, it is informative to look beyond the MS literature where associations between eye-tracking metrics and performance on the SDMT have been found in people with schizophrenia [22] and Huntington’s disease [23]

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