Motor Threshold Sample Clauses

Motor Threshold. Motor threshold (MT), is the minimum intensity of TMS pulse which elicits an MEP in half or more consecutive trials. This can be taken at rest - resting motor threshold, (RMT) or whilst the muscle is tonically activated - active motor threshold (AMT). AMT is always lower than RMT, because it takes less excitation for a post synaptic potential (EPSPs) to raise an active motorneuron to threshold than a neuron at rest. Motor threshold is believed to be reflecting activity in cortico-cortical axons and their synaptic contacts with corticospinal neurons. There are various methods of measuring the motor threshold. According to an international committee lead by (Xxxxxxx et al., 1994), the MT is the lowest stimulation intensity to reliably produce an MEP in 50% of 5-10 trials. The stimulus intensity should be commenced at 30% and increased in steps of 5% until this target is achieved, with a pre-determined particular amplitude (typically 50 microvolts) being defined as a reliable MEP for RMT, and 100 microvolts for AMT. In an alternative method proposed by (Xxxxx and Xxxxx, 1997) the coil is placed 5cm lateral to the vertex on the interaural line and is based on averaging two thresholds, an inferior threshold (maximum intensity which does not produce an MEP in 10 trials) and a super threshold (minimum intensity at which 10 MEPs are produced). Another method called adaptive threshold hunting, predicts or estimates for each pulse in the sequence a TMS intensity that yields a 50% probability of evoking an MEP. The pulse intensity chosen is taken from information obtained from the success of the previous stimuli to produce an MEP, (Awiszus, 2003). In this thesis, the method suggested by the international committee was adopted. This was chosen as it is the most recent method recommended by the international committee; furthermore it was utilised for the purposes of consistency as it was the method adopted in previously collected data by Xx Xxxxxxx Xxxxxxxxx whose control data is utilised for comparison with patient data collected in Chapter 6 and is the previously collected data in Chapter 5. Axon excitability is regulated by voltage gated sodium channels as demonstrated by a plethora of medication studies discussed in this chapter and so motor threshold may provide a marker of membrane excitability of both excitatory interneurons and corticospinal neurons in the motor cortex as well as the excitability of spinal motorneurons. The MT is obtained at the beginning of th...

Motor Threshold. Several studies in the literature have reported bilateral increases in MT in patients with chronic AED medicated focal epilepsy, (Xxxxxxxxx et al., 2000) (Xxxxx et al., 2005a) and in the ipsilateral compared with the contralateral hemisphere in drug naïve patients (Xxxxxx et al., 2007). In other drug naïve studies however the results are not convergent. (Xxxxxxx et al., 2000) for example found no difference in motor thresholds between patients with temporal and extratemporal focal epilepsy, these patients had ceased AED therapy for 48 hours before study. In TLE, (Xxxxxx et al., 2013b) observed that in the drug naïve state there was no difference between patients and controls, however there was a significant difference between hemispheres in patients, with increased MT in the ipsilateral hemisphere.