Posts Tagged SICI

[Abstract] Long-lasting effects of transcranial static magnetic field stimulation on motor cortex excitability

Abstract

Background

Transcranial static magnetic field stimulation (tSMS) was recently added to the family of inhibitory non-invasive brain stimulation techniques. However, the application of tSMS for 10–20 min over the motor cortex (M1) induces only short-lasting effects that revert within few minutes.

Objective

We examined whether increasing the duration of tSMS to 30 min leads to long-lasting changes in cortical excitability, which is critical for translating tSMS toward clinical applications.

Methods

The study comprised 5 experiments in 45 healthy subjects. We assessed the impact of 30-min-tSMS over M1 on corticospinal excitability, as measured by the amplitude of motor evoked potentials (MEPs) and resting motor thresholds (RMTs) to single-pulse transcranial magnetic stimulation (TMS) (experiments 1–2). We then assessed the impact of 30-min-tSMS on intracortical excitability, as measured by short-interval intracortical facilitation (SICF) and short-interval intracortical inhibition (SICI) using paired-pulse TMS protocols (experiments 2–4). We finally assessed the impact of 10-min-tSMS on SICF and SICI.

Results

30-min-tSMS decreased MEP amplitude compared to sham for at least 30 min after the end of the stimulation. This long-lasting effect was associated with increased SICF and reduced SICI. 10-min-tSMS –previously reported to induce a short-lasting decrease in MEP amplitude– produced the opposite changes in intracortical excitability, decreasing SICF while increasing SICI.

Conclusions

These results suggest a dissociation of intracortical changes in the consolidation from short-lasting to long-lasting decrease of corticospinal excitability induced by tSMS. The long-lasting effects of 30-min-tSMS open the way to the translation of this simple, portable and low-cost technique toward clinical trials.

via Long-lasting effects of transcranial static magnetic field stimulation on motor cortex excitability – Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation

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[Abstract] Decreased short-interval intracortical inhibition correlates with better pinch strength in patients with stroke and good motor recovery

Abstract

Background

Deeper short-interval intracortical inhibition (SICI), a marker of GABAA activity, correlates with better motor performance in patients with moderate to severe hand impairments in the chronic phase after stroke.

Objectives

We evaluated the correlation between SICI in the affected hemisphere and pinch force of the paretic hand in well-recovered patients. We also investigated the correlation between SICI and pinch force in controls.

Methods

Twenty-two subjects were included in the study. SICI was measured with a paired-pulse paradigm. The correlation between lateral pinch strength and SICI was assessed with Spearman’s rho.

Results

There was a significant correlation (rho = 0.69, p = 0.014) between SICI and pinch strength in patients, but not in controls. SICI was significantly deeper in patients with greater hand weakness.

Conclusions

These preliminary findings suggest that decreased GABAA activity in M1AH correlates with better hand motor performance in well-recovered subjects with stroke in the chronic phase.

via Decreased short-interval intracortical inhibition correlates with better pinch strength in patients with stroke and good motor recovery – Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation

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[Dissertation Abstract] Investigation of Neural Mechanisms of Grip Relaxation” by Binal Motawar

Abstract

Neural mechanisms for grip relaxation are relatively unknown and understudied, as compared to mechanisms for grip initiation. Yet, termination of motor activity is as important as initiation in daily function. This knowledge gap presents incomplete understanding of neural control of hand function and its impairment with aging and neurologic disorders.

The purpose of this dissertation was to identify and examine neural mechanisms of grip relaxation in healthy young adults, with aging, and in chronic stroke survivors. A series of experiments in healthy young adults showed that the relaxation from a maximum power grip was mediated by increase in the short-interval intracortical inhibition (SICI). The role of spinal motor excitability modulation for grip relaxation was refuted, in contrast to previous literature for the leg muscle. These data from healthy young adults suggest that the grip relaxation time is a cortically mediated active process. Additionally, these studies also showed that the neural mechanism of grip relaxation is comparable for the dominant and the nondominant hand in healthy young adults. The next step was to identify any delays in relaxing from a grip in healthy older adults.

Assessment of the effects of aging on the role of SICI showed that the delayed grip relaxation time in older adults was accompanied by reduced modulation of SICI for grip relaxation. The cortical silent period and H reflex did not explain delays in grip relaxation observed in older adults.

Another series of experiments showed that the chronic stroke survivors and age-matched control adults demonstrated comparable modulations of SICI, cortical silent period, corticomotor excitability, and H reflex. Yet, the paretic hand of the stroke survivors was significantly delayed in relaxing from a grip.

Correlation and regression analysis showed that the stroke-related delayed grip relaxation time may be explained by increased spasticity, reduced somatosensation, paretic grip weakness relative to the nonparetic, strength of the corticospinal connections and interhemispheric inhibition. An intervention aimed to modulate cortical excitability and interhemispheric inhibition, Active Passive Bilateral Therapy, was employed but was found to be not effective in modulating grip relaxation time and interhemispheric inhibition after a one-time 20-minute session, warranting a longer treatment time.

In summary, this dissertation investigated neural mechanisms of grip relaxation and contributes to the general body of knowledge regarding neural control of hand movements.

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