SICI Sample Clauses

SICI. If a pulse set below the AMT, named the conditioning stimulus (CS), is followed at intervals of 1-5 ms by a suprathreshold test stimulus (TS) this results in a phenomenon known as short-interval intra-cortical inhibition (SICI) (Xxxxxxx et al., 1993). It is believed that the response to the supra-threshold pulse is conditioned (MEP amplitude reduced/suppressed) by the sub-threshold pulse which activates cortical interneurons but not to a sufficient degree to result in an observable response from the muscle. The CS is believed to elicit short lasting IPSPs, inhibiting action potential generation by the EPSPs produced by the test pulse. The CS is set below AMT to ensure that it is sub- threshold for activation of the corticospinal projection, with the suprathreshold pulse set above RMT for the converse reason, to ensure that an MEP is produced. Furthermore, an identical CS that produces inhibition using TMS does not reduce the MEPs elicited by TES which activates corticospinal neurons directly (Xxxxxxxxx et al., 2008), indicating that SICI is a cortical phenomenon. In order to ascertain the mechanisms responsible for SICI (Xx Xxxxxxx et al., 1998) directly measured the descending volleys from epidural electrodes. The TS alone produced several I waves, with inhibition of the descending spinal volleys most pronounced at Interstimulus intervals (ISIs) of 1 ms and disappearing by ISIs of 5 ms. The I1 was virtually unattenuated unlike the other I waves. The researchers explain this by suggesting that the CS does not modify directly the excitability of pyramidal cells, and thus paired pulse TMS at ISIs of less than 5ms probably activates local corticocortical inhibitory circuits. In support of this, benzodiazepines (positive modulators of GABAa) enhance SICI, (Xxx et al., 2009), (Xxxx et al., 2002). Furthermore, the administration of the benzodiazepine lorazepam increases the inhibition of late I- waves but not the I1 wave during SICI (Xxxxx and Ugawa, 2002). Since the I1 wave remains unaffected, it is likely that the subthreshold conditioning stimulus enhances selectively GABAaergic neurotransmission leading to suppression of the late I-waves. It is important to ensure that the muscle is at rest as voluntary contraction has been shown to significantly reduce the amount of SICI, (Ridding et al., 1995).