scholarly journals Duration and reliability of the silent period in individuals with spinal cord injury

2020 ◽  
Author(s):  
Hannah Sfreddo ◽  
Jaclyn R. Wecht ◽  
Ola Alsalman ◽  
Yu-Kuang Wu ◽  
Noam Y. Harel
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Evoked Potential ◽  
Motor Evoked Potential ◽  
Silent Period ◽  
List Type ◽  
Abductor Pollicis Brevis ◽  
Resting Motor Threshold ◽  
Cord Injury ◽  
Period Duration

ObjectiveWe aim to better understand the silent period (SP), an inhibitory counterpart to the well-known motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS), in individuals with spinal cord injury (SCI).MethodsElectromyographic responses were measured in the target abductor pollicis brevis at rest (TMS at 120% of resting motor threshold (RMT)) and during maximal effort (TMS at 110% of RMT). Participants with chronic cervical SCI (n=9) and able-bodied volunteers (n=12) underwent between 3-7 sessions of stimulation on separate days. The primary outcomes were the magnitude and reliability of SP duration, resting and active MEP amplitudes, and RMT.ResultsSCI participants showed significantly increased RMT, decreased MEP amplitudes, and non-significantly longer SP duration compared to AB participants. In contrast to high inter-participant variability, SP duration demonstrated reduced intra-participant variability within and across sessions compared with resting and active MEP amplitudes. SCI participants also demonstrated a higher prevalence of SP ‘interruptions’ compared to AB participants.ConclusionsSP reflects a balance between corticospinal excitatory and inhibitory processes. SP duration is more reliable within and across multiple sessions than MEP amplitude.SignificanceThe higher reliability of SP duration may make it a useful outcome measure for future trials of SCI interventions.HighlightsWe compared characteristics of the silent period between individuals with spinal cord injury and able-bodied volunteers.Silent period duration was insignificantly longer in spinal cord injury individuals.Silent period duration was found to be a more reliable within-subject metric than motor evoked potential amplitude.

scholarly journals Operant conditioning of the tibialis anterior motor evoked potential in people with and without chronic incomplete spinal cord injury

2018 ◽  
Vol 120 (6) ◽  
pp. 2745-2760 ◽  
Author(s):  
Aiko K. Thompson ◽  
Rachel H. Cote ◽  
Janice M. Sniffen ◽  
Jodi A. Brangaccio
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Operant Conditioning ◽  
Tibialis Anterior ◽  
Evoked Potential ◽  
Motor Evoked Potential ◽  
Silent Period ◽  
Incomplete Spinal Cord Injury ◽  
Function Recovery ◽  
Cord Injury

The activity of corticospinal pathways is important in movement control, and its plasticity is essential for motor skill learning and re-learning after central nervous system (CNS) injuries. Therefore, enhancing the corticospinal function may improve motor function recovery after CNS injuries. Operant conditioning of stimulus-induced muscle responses (e.g., reflexes) is known to induce the targeted plasticity in a targeted pathway. Thus, an operant conditioning protocol to target the corticospinal pathways may be able to enhance the corticospinal function. To test this possibility, we investigated whether operant conditioning of the tibialis anterior (TA) motor evoked potential (MEP) to transcranial magnetic stimulation can enhance corticospinal excitability in people with and without chronic incomplete spinal cord injury (SCI). The protocol consisted of 6 baseline and 24 up-conditioning/control sessions over 10 wk. In all sessions, TA MEPs were elicited at 10% above active MEP threshold while the sitting participant provided a fixed preset level of TA background electromyographic activity. During baseline sessions, MEPs were simply measured. During conditioning trials of the conditioning sessions, the participant was encouraged to increase MEP and was given immediate feedback indicating whether MEP size was above a criterion. In 5/8 participants without SCI and 9/10 with SCI, over 24 up-conditioning sessions, MEP size increased significantly to ~150% of the baseline value, whereas the silent period (SP) duration decreased by ~20%. In a control group of participants without SCI, neither MEP nor SP changed. These results indicate that MEP up-conditioning can facilitate corticospinal excitation, which is essential for enhancing motor function recovery after SCI. NEW & NOTEWORTHY We investigated whether operant conditioning of the motor evoked potential (MEP) to transcranial magnetic stimulation can systematically increase corticospinal excitability for the ankle dorsiflexor tibialis anterior (TA) in people with and without chronic incomplete spinal cord injury. We found that up-conditioning can increase the TA MEP while reducing the accompanying silent period (SP) duration. These findings suggest that MEP up-conditioning produces the facilitation of corticospinal excitation as targeted, whereas it suppresses inhibitory mechanisms reflected in SP.

scholarly journals Operant conditioning of the motor-evoked potential and locomotion in people with and without chronic incomplete spinal cord injury

2019 ◽  
Vol 121 (3) ◽  
pp. 853-866 ◽  
Author(s):  
Aiko K. Thompson ◽  
Gina Fiorenza ◽  
Lindsay Smyth ◽  
Briana Favale ◽  
Jodi Brangaccio ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Operant Conditioning ◽  
Motor Function ◽  
Evoked Potential ◽  
Motor Evoked Potential ◽  
Incomplete Spinal Cord Injury ◽  
Function Recovery ◽  
Cord Injury ◽  
Ankle Dorsiflexor

Foot drop is very common among people with chronic incomplete spinal cord injury (SCI) and likely stems from SCI that disturbs the corticospinal activation of the ankle dorsiflexor tibialis anterior (TA). Thus, if one can recover or increase the corticospinal excitability reduced by SCI, motor function recovery may be facilitated. Here, we hypothesized that in people suffering from weak dorsiflexion due to chronic incomplete SCI, increasing the TA motor-evoked potential (MEP) through operant up-conditioning can improve dorsiflexion during locomotion, while in people without any injuries, it would have little impact on already normal locomotion. Before and after 24 MEP conditioning or control sessions, locomotor electromyography (EMG) and kinematics were measured. This study reports the results of these locomotor assessments. In participants without SCI, locomotor EMG activity, soleus Hoffmann reflex modulation, and joint kinematics did not change, indicating that MEP up-conditioning or repeated single-pulse transcranial magnetic stimulation (i.e., control protocol) does not influence normal locomotion. In participants with SCI, MEP up-conditioning increased TA activity during the swing-to-swing stance transition phases and ankle joint motion during locomotion in the conditioned leg and increased walking speed consistently. In addition, the swing-phase TA activity and ankle joint motion also improved in the contralateral leg. The results are consistent with our hypothesis. Together with the previous operant conditioning studies in humans and rats, the present study suggests that operant conditioning can be a useful therapeutic tool for enhancing motor function recovery in people with SCI and other central nervous system disorders. NEW & NOTEWORTHY This study examined the functional impact of operant conditioning of motor-evoked potential (MEP) to transcranial magnetic stimulation that aimed to increase corticospinal excitability for the ankle dorsiflexor tibialis anterior (TA). In people with chronic incomplete spinal cord injury (SCI), MEP up-conditioning increased TA activity and improved dorsiflexion during locomotion, while in people without injuries, it had little impact on already normal locomotion. MEP conditioning may potentially be used to enhance motor function recovery after SCI.

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