Influence of stimulation intensity on paired-pulse suppression of human median nerve somatosensory evoked potentials

Abstract

Paired-pulse stimulation, the application of two stimuli in close succession, is a useful tool to investigate cortical excitability. Suppression of the second response after short interstimulus intervals characterizes paired-pulse behavior. Although paired-pulse suppression is often studied as a marker of cortical excitability in humans, little is known about the influence of stimulation intensity on paired-pulse suppression. To systematically explore the effect of stimulus intensity on paired-pulse suppression of median nerve somatosensory evoked potentials (MNSEPs), we recorded single-pulse or paired-pulse MNSEPs in healthy volunteers using stimulation intensities ranging from the sensory threshold to 1.2 times the motor threshold using interstimulus intervals of 10, 30, and 100 ms. Of the various somatosensory evoked potential components, only the N20-P25 component showed an effect of intensity, where higher intensities resulted in stronger paired-pulse suppression. However, when only intermediate intensities were considered, paired-pulse suppression was not or only weakly influenced. Our data suggest that stimulation intensity in contrast to single pulse-evoked MNSEPs has only a weak influence on the paired-pulse suppression of early MNSEPs. Paired-pulse suppression is believed to arise from inhibition generated by intracortical networks. The lack of intensity dependence within the range tested can be considered as a step toward creating invariance against fluctuations of stimulus intensity. Thus, intracortical computations as apparent in paired-pulse behavior might be characterized by different properties compared with feed-forward processing.

Rapid-Rate Paired Associative Stimulation over the Primary Somatosensory Cortex

“…For SEP analysis, the N20 was calculated as the difference between the baseline EMG and the first negative inflection after the stimulus, the peak-to-peak amplitude of N20-P25 was assessed as the difference between the N20 and the subsequent positive inflection and the P25 was calculated as the difference between the N20-P25 and the N20 [ 8 , 9 , 33 ]. Paired-pulse inhibition was expressed as a ratio of the amplitudes of the second N20-P25 (i.e.…”

Modulation of human corticospinal excitability by paired associative stimulation

“…Lakhani et al, 2012; Gatica Tossi et al, 2013), an effect that remains evident at 2.5 times MT (Urasaki et al, 1998). While components of the S1 SEP appear to saturate at some point below the pain threshold (PT) (Parain and Delapierre, 1991), MEG recordings suggest that the asymptote of the S2 response occurs at lower stimulation intensities than for the S1 response (Lin et al, 2003).…”

A single dose of lorazepam reduces paired‐pulse suppression of median nerve evoked somatosensory evoked potentials

“…Accordingly, small amplitude ratios are associated with strong PPS, and large amplitude ratios are associated with reduced PPS. For the somatosensory system, PPS in combination with somatosensory evoked potential (SEP) recordings over the primary somatosensory cortex has been increasingly used to investigate paired‐pulse behaviour, in order to obtain insights into cortical processing modes and to obtain markers of changes of cortical excitability attributable to learning or pathological states (Allison, ; Schwartz & Shagass, ; Shagass & Schwartz, ; Ragert et al ., ; Höffken et al ., , ,b; Lenz et al ., ; Gatica Tossi et al ., ).…”