Exploring the effect of the nerve conduction distance on the MScanFit method ofmotor unit number estimation (MUNE).

OBJECTIVE: MScanFit motor unit number estimation (MUNE) is a sensitive method for detecting motor unit loss and has demonstrated high reproducibility in various settings. In this study, our aim was to assess the outputs of this method when the nerve conduction distance is increased. METHODS: MScanFit recordings were obtained from the abductor digiti minimi muscle of 20 healthy volunteers. To evaluate the effect of nerve conduction distance, the ulnar nerve was stimulated from the wrist and elbow respectively. Reproducibility of MUNE, compound muscle action potential (CMAP), and other motor unit parameters were assessed using intraclass correlation coefficients (ICCs). RESULTS: Motor unit numbers obtained from stimulation at the wrist and elbow did not significantly differ and exhibited strong consistency in the ICC test (120.3 ± 23.7 vs. 118.5 ± 27.9, p > 0.05, ICC: 0.88). Similar repeatability values were noted for other parameters. However, the Largest Unit (%) displayed notable variability between the two regions and exhibited a negative correlation with nerve conduction distance. CONCLUSION: Our findings indicate that MScanFit can consistently calculate motor unit numbers and most of its outputs without substantial influence from nerve conduction distance. Exploring MScanFit's capabilities in various settings could enhance our understanding of its strengths and limitations for extensive use in clinical practice.

Long-interval afferent inhibition measurement using two different methods: Normative values, repeatability and reliability.

BACKGROUND: The mechanism of Short-Latency Afferent Inhibition (SAI) is relatively well understood. In contrast, Long-Latency Afferent Inhibition (LAI) has not been as extensively studied as SAI, and its underlying mechanism remains unclear. OBJECTIVE/HYPOTHESIS: This study had two primary objectives: first, to determine the optimal ISIs for LAI measured by amplitude changes (A-LAI) using high-resolution ISI ranges; and second, to compare measurements of LAI by threshold-tracking (T-LAI). METHODS: Twenty-eight healthy volunteers (12 males aged 24- 45 years) participated in the study. Paired peripheral electrical and transcranial magnetic stimulation (TMS) stimuli (TS1mv) were applied at varying (ISIs)- 100, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700, 800, 900, 1000 ms. RESULTS: Both A-LAI and T-LAI showed that LAI decreased progressively from a peak at 200 or 250 ms to 1000 ms. Using the A-LAI method, pronounced inhibition was observed at three specific ISIs: 100 ms, 250 ms and 450 ms. When A-LAI values were converted to equivalent threshold changes, they did not differ significantly from T-LAI. Reliability at distinguishing individuals, as indicated by intraclass correlation coefficient (ICC) was greater for A-LAI, with a peak value of 0.82 at 250 ms. CONCLUSION(S): The study demonstrates that ISIs of 100 ms and 250 ms can be reliably used in amplitude measurement LAI. The study demonstrates that both LAI measurements record a similar decline of inhibition with increasing ISI.

Feasibility and reliability of MScanFit motor unit number estimation in peroneus longus muscle.

INTRODUCTION/AIMS: Motor unit number estimation (MUNE) methods may be valuable to detect motor involvement earlier than compound muscle action potential (CMAP) amplitude. The most recent MUNE method, MScanFit, has been shown to have advantages compared with previously described methods. However, MScanFit has only been applied in a few lower extremity muscles. In this study we examined the feasibility and reliability of MScanFit in peroneus longus muscle. METHODS: Twenty healthy controls (16 males and 4 females; mean age, 36.05 ± 2.58 years) were examined twice within a 1- to 2-week interval. Fibular nerve was stimulated at the knee and CMAP scans were recorded from peroneus longus muscle. From this, MScanFit MUNE and size parameters were calculated, as was the CMAP amplitude. The reliability was examined using coefficient of variation (CV) and intraclass correlation coefficient (ICC). MUNE was correlated with CMAP amplitude using linear regression analysis. RESULTS: The CV between sessions was higher for CMAP amplitude (11.63 ± 1.88%) than MScanFit MUNE (3.13 ± 0.78%). Among the size parameters, mean unit amplitude (µV) showed the lowest CV (11.46 ± 1.77%). Using ICC, CMAP amplitude exhibited good reliability (0.787), whereas that of MScanFit MUNE was excellent (0.902). Reliability was good for all size parameters. There was no significant correlation between MScanFit MUNE and CMAP amplitude (R = 0.25, P > .05). DISCUSSION: MScanFit MUNE is feasible in the peroneus longus muscle, with high test-retest reliability in healthy subjects. Studies in patients are needed to examine the sensitivity of this muscle in disease.

Estimating the motor unit number of the flexor carpi ulnaris muscle with MScanFit MUNE.

INTRODUCTION/AIMS: MScanFit motor unit number estimation (MUNE) is a promising method for motor unit estimation and is reported to have good reliability in distal and small muscles. In this study, we investigated the reliability of MScanFit MUNE in a proximal forearm muscle, the flexor carpi ulnaris. METHODS: Twenty healthy volunteers were included in this study, and 15 participants were re-evaluated in a second session. The ulnar nerve was stimulated at the elbow and a compound muscle action potential (CMAP) scan from the flexor carpi ulnaris (FCU) muscle was recorded from each arm. CMAP, MUNE, and other motor unit parameters were obtained. Reproducibility was evaluated using intraclass correlation coefficients (ICCs). RESULTS: The average MUNE from 40 FCU muscles was 90.9 (standard deviation: 16.4). MScanFit MUNE and CMAP were not significantly different between the dominant and non-dominant sides. The ICC indicated good reliability between sessions for each side (0.81 and 0.8, respectively). DISCUSSION: Our results indicate that MScanFit MUNE is a feasible method with good reproducibility for MUNE of the FCU muscle.

Short latency afferent inhibition: comparison between threshold-tracking and conventional amplitude recording methods.

Short-latency afferent inhibition (SAI), which is conventionally measured as a reduction in motor evoked potential amplitude (A-SAI), is of clinical interest as a potential biomarker for cognitive impairment. Since threshold-tracking has some advantages for clinical studies of short-interval cortical inhibition, we have compared A-SAI with a threshold-tracking alternative method (T-SAI). In the T-SAI method, inhibition was calculated by tracking the required TMS intensity for the targeted MEP amplitude (200 uV) both for the test (TMS only) and paired (TMS and peripheral stimulation) stimuli. A-SAI and T-SAI were recorded from 31 healthy subjects using ten stimuli at each of 12 inter-stimulus intervals, once in the morning and again in the afternoon. There were no differences between morning and afternoon recordings. When A-SAI was normalized by log conversion it was closely related to T-SAI. Between subjects, variability was similar for the two techniques, but within-subject variability was significantly smaller for normalized A-SAI. Conventional amplitude measurements appear more sensitive for detecting changes within-subjects, such as in interventional studies, but threshold-tracking may be as sensitive as detecting abnormal SAI in a patient.

Body ownership, sensorimotor integration and motor cortical excitability: A TMS study about rubber hand illusion.

OBJECTIVE: The Rubber Hand Illusion (RHI) manipulates body ownership experimentally and helps investigate the related neurophysiological processes. This study aimed to evaluate motor cortex excitability that hypothesized changed due to illusion. METHOD: Twenty-one healthy (twelve male, nine female), right-handed volunteers aged between 25 and 50 years were recruited to the study. Short-Latency Afferent Inhibition (SAI) was evaluated by transcranial magnetic stimulation (TMS) given with a figure-of-eight-shaped coil from the left motor cortex, 21 ms after peripheral electrical stimulation. Short-Interval Intracortical Inhibition (SICI) and Intracortical Facilitation (ICF) were investigated using a paired-pulse TMS at interstimulus intervals (ISI) of 1, 2.5, 3 ms and 15, 20, 25 ms, respectively. We used custom-made illusion setups for TMS paradigms. SAI, SICI and ICF was evaluated before, during and 15 min after the RHI. RESULTS: Results of the study revealed significantly high SAI during illusion compared to pre-illusion, but no difference was found between post-illusion 15th minutes and control measurements. Significantly reduced SICI at 2.5 and 3 ms ISI obtained during illusion, while RHI did not affect SICI at 1 ms ISI and ICF. SIGNIFICANCE: Body ownership illusion modulates the motor cortex excitability, possibly through altered sensory processing and sensorimotor integration.

Monocyte to high-density lipoprotein cholesterol ratio is associated with the presence of carotid artery disease in acute ischemic stroke.

Aim: Monocyte to high-density lipoprotein cholesterol ratio (MHR) has recently emerged as a predictor of cardio-cerebrovascular diseases. Since around one-fifth of strokes are linked to atherosclerosis carotid artery, we aimed to present the relationship between carotid artery disease (CAD) and MHR value in acute ischemic stroke (AIS). Materials & methods: A total of 209 adult AIS patients analyzed. Patients divided into two groups in respect to the existence of CAD. MHR was compared between the two groups. Results: MHR with a cut off of 17.23 predicted the presence of disease in the carotid artery, with a sensitivity of 91.9% and specificity of 66.7. MHR was the independent predictor for the presence of disease in the carotid artery. Conclusion: MHR was found to be an independent predictor for the CAD in AIS. Therefore, in AIS patients with high MHR value, CAD should be examined more carefully.

Reduced Short-Latency Afferent Inhibition Indicates Impaired Sensorimotor Integrity During Migraine Attacks.

BACKGROUND AND OBJECTIVE: Migraine attacks disrupt sensory information processing and may also disturb sensorimotor integration. This prospective pilot study aimed to assess the sensorimotor integration and inhibitory circuitry in the sensorimotor cortex using short-latency afferent inhibition (SAI) paradigm in migraine. METHODS: Twenty-five migraine without aura patients (10 interictal, 5 preictal, 10 ictal) and 16 healthy controls were enrolled. SAI was elicited by combining the right median nerve electrical stimulation and left motor cortical magnetic stimulation at the 21-millisecond interval. Mean motor evoked potential (MEP) amplitude ratio, recorded from right abductor pollicis muscle after single and conditioned stimulations, was calculated as SAI. RESULTS: Average MEP inhibition ratio after single and conditioned stimuli in healthy controls was not significantly different from interictal patients (45.1% ± 20.3% vs 44.5% ± 14.75% [P = .93]). However, SAI was significantly reduced during preictal/prodromal (-14.6% ± 42.8% [P = .002]) and ictal/headache (-7.4% ± 31.1% [P = .0001]) periods of migraine compared to healthy controls. CONCLUSION: Pronounced decrease in SAI during preictal and ictal periods in migraine was shown for the first time. Instead of inhibition to a conditioned stimulus, facilitation in the sensorimotor cortex was detected both ictally and preictally. Preictal SAI results suggest the presence of increased excitability state several hours prior to the headache phase. This phenomenon could be related to the cortical hyperresponsivity to sensory stimuli and cognitive disturbances accompanying migraine attacks as SAI is modulated by cholinergic activity.

The effect of the anodal transcranial direct current stimulation over the cerebellum on the motor cortex excitability.

This study was designed to investigate whether the cerebellum has an inhibitory effect on motor cortical excitability. Sixteen healthy adults (age range, 25-50 years, five female) participated in the study. Anodal cerebellar transcranial direct current stimulation (a-cTDCS) was used to modulate cerebellar excitability. A-cTDCS was given for 20 min at 1 mA intensity. The automatic threshold tracking method was used to investigate cortical excitability. Resting motor threshold (RMT), short interval intracortical inhibition (SICI), short interval intracortical facilitation (SICF), intracortical facilitation (ICF), and the input output curve (I-O curve) were motor cortical excitability parameters. a-cTDCS caused a reduction in overall SICI and the reduced SICF for interstimulus intervals (ISIs) to 2.4-4.4 ms. a-cTDCS has no effect on ICF, RMT, and the I-O curve. There were no significant changes in any of these cortical excitability parameters after sham cTDCS. Results of the study indicate that a-cTDCS has a dual (both inhibitory and excitatory) effect on motor cortical excitability, rather than a simple inhibitory effect. The cerebellum modulates both the inhibitory and facilitatory activities of motor cortex (M1) and suggest that cerebello-cerebral motor connectivity is more complex than solely inhibitory or facilitatory connections.