Differentiation of motor evoked potentials elicited from multiple forearm muscles: An investigation with high-density surface electromyography

Synergy Analysis of Back Muscle Activities in Patients with Adolescent Idiopathic Scoliosis Based on High-Density Electromyogram

Adolescent idiopathic scoliosis (AIS) is a common structural spinal deformity and is typically associated with altered muscle properties. However, it is still unclear how muscle activities and the underlying neuromuscular control are changed in the entire scoliotic zone, restricting the corresponding pathology investigation and treatment enhancements. In this study, high-density electromyogram (HD-EMG) was utilized to explore the neuromuscular synergy of back muscle activities. For each of ten AIS patients and ten healthy subjects for comparison, a high-density electrode array was placed on their back from T8 to L4 to record EMG signals when performing five spinal motions (flexion/extension, lateral bending, axial rotation, siting, and standing). From the HD-EMG recordings, muscle synergies were extracted using the non-negative matrix factorization method and the topographical maps of EMG root-mean-square were constructed. For both the AIS and healthy subjects, the experimental results indicated that two muscle synergy groups could explain over 90% of recorded muscle activities for all five motions. During flexion/extension, the patients presented statistically significant higher activations on the convex side in the entire root-mean-square maps and synergy vector maps (p <0.05). During lateral bending and axial rotation, the patients exhibited less activated muscles on the dominant actuating side relative to the contralateral side and their synergy vector maps showed a less homogenous and more diffuse distribution of muscle contraction with statistically different centers of gravity. The findings suggest that a scoliotic spine might adopt an altered modular muscular coordination strategy to actuate different dominant muscles as adapted compensations for the deformation.

Mapping Responses of Lumbar Paravertebral Muscles to Single-Pulse Cortical TMS Using High-Density Surface Electromyography

Motor evoked potential (MEP), which was elicited by transcranial magnetic stimulation (TMS), has been widely used to detect corticospinal projection from TMS cortical site to trunk muscles. It can help to find the stimulation hotspot in the scalp. However, it fails to precisely describe coordinated activities of trunk muscle groups with only single-channel myoelectric signal. In this study, we aimed to use high-density surface electromyography (sEMG) to explore the effect of cortical TMS on lumbar paravertebral muscles in healthy subjects. The cortical site at 1 cm anterior and 4 cm lateral to vertex was chosen to simulate using a single-pulse TMS with different intensities and forward-bending angles. A high-density electrode array (45 channels) was placed on the surface of lumbar paravertebral muscles to record sEMG signals during a TMS experiment. MEP signals elicited by TMS were extracted from 45-channel recordings and one topographic map of the MEP amplitudes with six spatial features was constructed at each sampling point. The results showed TMS could successfully evoke an oval area with high intensity in the MEP topographic map, while this area mainly located in ipsilateral side of the TMS site. Intensity features related to the high intensity area rose significantly with TMS intensity and forward-bending angle increasing, but location features showed no change. The optimal stimulation parameters were 80% of maximum stimulator output (MSO) for TMS intensity and 30/60 degree for forward-bending angle. This study provided a potentially effective mapping tool to explore the hotspot for transcranial stimulation on trunk muscles.

Motor potential evoked by transcranial magnetic stimulation depends on the placement protocol of recording electrodes: a pilot study

OBJECTIVE

There seems to be no consensus in the literature regarding the protocol of surface electromyography (sEMG) electrode placement for recording motor evoked potentials (MEP) in transcranial magnetic stimulation (TMS) applications. Thus, the aim of this study was to investigate the effect on the MEP amplitude bytwo different protocols for electrode placement.

METHODS

sEMG electrodes were placed on three upper arm muscles (biceps brachii, flexor carpi radialis, and flexor pollicis brevis) of six right-handed subjects following two different protocols (1 and 2), which varied according to the interelectrode distance and location relative to the muscle. TMS pulses were applied to the hotspot of biceps brachii, while sEMGwas recorded from the two protocols and for each muscle simultaneously.

MAIN RESULTS

Greater MEP amplitudes were obtained for Protocol 1 compared to Protocol 2 (P < 0.05).

SIGNIFICANCE

Different electrode placement protocols may result in distinct MEP amplitudes, which should be taken into account when adjusting the intensity on single and repetitive TMS sessions.

Using transcranial magnetic stimulation to map the cortical representation of lower-limb muscles

Objective

To evaluate the extent to which transcranial magnetic stimulation (TMS) can identify discrete cortical representation of lower-limb muscles in healthy individuals.

Methods

Motor evoked potentials were recorded from resting vastus medialis, rectus femoris, vastus lateralis, medial and lateral hamstring, and medial and lateral gastrocnemius muscles on the right leg of 16 young healthy adults using bipolar surface electrodes. TMS was delivered through a 110-mm double-cone coil at 63 sites over the left hemisphere. Location and size of cortical representation and number of discrete peaks were quantified.

Results

Within the quadriceps group there was a main effect of muscle on anterior-posterior centre of gravity (p = 0.010), but the magnitude of the difference was small. There was also a main effect of muscle on medial-lateral hotspot (p = 0.027) and map volume (p = 0.047), but no post-hoc tests were significant. The topography of each lower-limb muscle was complex and variable across individuals.

Conclusions

TMS delivered with a 110-mm double-cone coil could not reliably identify discrete cortical representations of resting lower-limb muscles when responses were measured using bipolar surface electromyography.

Significance

The characteristics of the cortical representation provide a basis against which to evaluate cortical reorganisation in clinical populations.

Mechanisms of Transcranial Magnetic Stimulation Treating on Post-stroke Depression

Post-stroke depression (PSD) is a neuropsychiatric affective disorder that can develop after stroke. Patients with PSD show poorer functional and recovery outcomes than patients with stroke who do not suffer from depression. The risk of suicide is also higher in patients with PSD. PSD appears to be associated with complex pathophysiological mechanisms involving both psychological and psychiatric problems that are associated with functional deficits and neurochemical changes secondary to brain damage. Transcranial magnetic stimulation (TMS) is a non-invasive way to investigate cortical excitability via magnetic stimulation of the brain. TMS is currently a valuable tool that can help us understand the pathophysiology of PSD. Although repetitive TMS (rTMS) is an effective treatment for patients with PSD, its mechanism of action remains unknown. Here, we review the known mechanisms underlying rTMS as a tool for better understanding PSD pathophysiology. It should be helpful when considering using rTMS as a therapeutic strategy for PSD.