Highlights
- •Scores on the SDMT represent deficits in sensorial, cognitive or motor processing.
- •There is a need to isolate and characterise cognitive IPS deficits in MS.
- •We demonstrated significant cognitive IPS deficits in early MS patients.
- •Cognitive IPS deficits were not associated with SDMT performance.
Abstract
Background
The assessment of cognitive information processing speed (IPS) is complicated in MS,
with altered performance on tests such as the Symbol Digit Modalities Test (SDMT)
potentially representing changes not only within cognitive networks but in the initial
sensorial transmission of information to cognitive networks, and/or efferent transmission
of the motor response.
Objective
We aimed to isolate and characterise cognitive IPS deficits in MS using ocular motor
tasks; a prosaccade task (used to assess and control for sensorial and motor IPS)
which was then used to adjust performance on the Simon task (cognitive IPS).
Methods
All participants (22 MS patients with early disease, 22 healthy controls) completed
the ocular motor tasks and the SDMT. The Simon task assessed cognitive IPS by manipulating
the relationship between a stimulus location and its associated response direction.
Two trial types were interleaved: (1) congruent, where stimulus location = response
direction; or (2) incongruent, where stimulus location ≠ response direction. RESULTS
MS patients did not perform differently to controls on the SDMT. For OM tasks, when
sensorial and motor IPS was controlled, MS patients had significantly slower cognitive
IPS (incongruent trials only) and poorer conflict resolution. SDMT performance did
not correlate with slower cognitive IPS in MS patients, highlighting the limitation
of using SDMT performance to interpret cognitive IPS changes in patients with MS.
Conclusion
Cognitive IPS deficits in MS patients are dissociable from changes in other processing
stages, manifesting as impaired conflict resolution between automatic and non-automatic
processes. Importantly, these results raise concerns about the SDMT as an accurate
measure of cognitive IPS in MS.
Keywords
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Article info
Publication history
Published online: November 21, 2019
Accepted:
November 11,
2019
Received in revised form:
November 7,
2019
Received:
March 22,
2019
Identification
Copyright
© 2019 Published by Elsevier B.V.
