Rudimentary Dexterity Corresponds With Reduced Ability to Move in Synergy After Stroke: Evidence of Competition Between Corticoreticulospinal and Corticospinal Tracts?
Merav R Senesh, Karina Barragan, David J Reinkensmeyer
PMID 32830602WHAT IT FOUND
In people with moderate arm impairment after stroke, the ability to move the arm out of synergy and the ability to move within synergy trade off against each other.
This suggests a competition between brain pathways, where recovering fine control may temporarily reduce gross synergy movement.
Key findings
01For subjects in the moderate impairment range, scores for out-of-synergy movement were negatively correlated with scores for in-synergy movement.
02The fraction of subjects able to fully perform flexor and extensor synergies did not increase as quickly as total UEFM score increased into the range 35–39, while out-of-synergy movement ability began to increase substantially.
03The ability to perform arm movements emerged before the ability to perform dexterous hand movements, with hand dexterity scores increasing above zero around a UEFM score of 22.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The study relied on archived data from multiple sources, which may introduce variability. The UEFM is a coarse scale with only three grading levels per item, limiting the resolution of motor control assessment. No imaging or neurophysiological data (such as MRI or DTI) was collected to directly confirm the use of specific brain pathways (CST vs CRST); the conclusions about pathway competition are behavioral inferences. The analysis excluded some UEFM items (reflexes, finger-to-nose) due to scoring inconsistencies or lack of correlation with other items. The study design is cross-sectional/cohort based on existing data, so it describes associations at different impairment levels rather than tracking individual longitudinal recovery trajectories.
Declared interests
The authors declare that there is no conflict of interest. The work was supported by N.I.H. grants.
The easy way to misread this
Do not interpret the negative correlation between in-synergy and out-of-synergy scores as proof that the brain pathways are physically competing or switching. The study infers this from behavioral data without imaging confirmation. Also, do not assume this trade-off occurs in all patients; it was only significant in the moderate impairment range (UEFM ~30-40), not in severe or mild cases.