Rudimentary Dexterity Corresponds With Reduced Ability to Move in Synergy After Stroke: Evidence of Competition Between Corticoreticulospinal and Corticospinal Tracts?

Abstract

Objective When a stroke damages the corticospinal tract (CST), it has been hypothesized that the motor system switches to using the corticoreticulospinal tract (CRST) resulting in abnormal arm synergies. Is use of these tracts mutually exclusive, or can the motor system spontaneously switch between them depending on the type of movement it wants to make? If the motor system can share control at will, then people with a rudimentary ability to make dexterous movements should be able to perform synergistic arm movements as well. Methods We analyzed clinical assessments of 319 persons’ abilities to perform “out-of-synergy” and “in-synergy” arm movements after chronic stroke using the Upper Extremity Fugl-Meyer (UEFM) scale. Results We identified a moderate range of arm impairment (UEFM = ~30-40) where subjects had a rudimentary ability to make out-of-synergy (~23%-50% on the out-of-synergy score) and dexterous hand movements (~3-10 blocks on Box and Blocks Test). Below this range persons could perform in-synergy but not out-of-synergy or dexterous movements. In the moderate range, however, scoring better on out-of-synergy movements correlated with scoring worse on in-synergy movements ( P = .001, r ≈ −0.6). Conclusion Rudimentary dexterity corresponded with reduced ability to move the arm in-synergy. This finding supports the idea that CST and CRST compete and has implications for rehabilitation therapy.

Startle Increases the Incidence of Anticipatory Muscle Activations but Does Not Change the Task-Specific Muscle Onset for Patients After Subacute Stroke

“…As we have learned, the premotor cortex is mainly responsible for motor planning and preparation, and the excessive excitability of these areas would induce reinforced inhibition to the cortical reticulospinal tract ( 44 ) and consequently affect the modulation of task-specific AMAs. This was supported by the lower incidence of ECR AMAs and positive SE response, which may reflex the impaired cortical reticulospinal tract after stroke ( 22 , 44 ). Therefore, rehabilitation interventions for the impaired cortical reticulospinal tract may be helpful for the recovery of AMAs after stroke.…”

“…The second limitation of our study was that our experiment did not strictly limit the severity of motor impairment of participants. The large difference in FMA score may indicate different dominant neural pathways they rely on ( 22 ), which may lead to unstable results. Stroke survivors within different motor function levels may use different motor synergies of flexors and extensors ( 22 ) and perform different AMA responses.…”

“…The large difference in FMA score may indicate different dominant neural pathways they rely on ( 22 ), which may lead to unstable results. Stroke survivors within different motor function levels may use different motor synergies of flexors and extensors ( 22 ) and perform different AMA responses. Stratified analysis should be necessary according to the subject's motor function states in further researches with a higher sample size.…”

Possibility that extensors respond faster than flexors for the metacarpophalangeal joints in individuals with severe-to-moderate stroke-caused impairment: A pilot study

“…The second possibility of different neural routes resulting in differences in intiniation and termination delays could be that MCP flexors and extensors have different pathways to the motor neuron pools from either of the reticulospinal tract or the corticospinal tract. It is accompanied by the assumption that the reticulospinal tract and corticospinal tract compete [36], meaning that differences in intiniation and termination delays might not occur in the tract level. It is known that the median nerve innervates MCP flexors while the radial nerve innervates MCP extensors [4], [37].…”

A major new dimension in the problem of brain injury

“…They studied neurohormonal effects in the first few hours after injury; thus, the long-term effects are unknown. For example, neurohormones might contribute to the abnormal movement patterns that emerge after stroke (e.g., Senesh et al, 2020 ). Knowledge of their acute and chronic effects could help shape the design of new therapeutic regimens, both in general and for individual patients; appropriate treatments may well differ depending on which side of the brain is injured.…”