Modulation of somatosensory evoked fields from SI and SII by acute GABA A -agonism and paired-pulse stimulation

Modulation of somatosensory evoked magnetic fields by intensity of interfering stimuli in human somatosensory cortex: An MEG study

“…Thus, they proposed that these components may be related to IPSPs generated by GABAergic interneurons, as IPSP activity is known to be attenuated by frequent stimuli with a short ISI (Deisz and Prince, 1989). This hypothesis was supported by the recent pharmacological approach, which showed reduction in P35m and P60m responses by GABA A agonist lorazepam in the single pulse condition (Huttunen et al, 2008). Furthermore, they observed that P35m showed similar recovery cycles of IPSPs, which was a relatively long recovery cycle, in the paired-pulse condition.…”

“…It has been suggested that the earliest SEF deflection (N20m) from S1 following electrical stimulation to the median nerve reflects excitatory postsynaptic potentials (EPSPs) arising from excitation of the basal dendrites of pyramidal neurons in area 3b (Ikeda et al, 2005;Wikström et al, 1996). This notion is supported by the finding that N20m showed similar recovery cycles of EPSPs in the paired-pulse stimulation experiment (Huttunen et al, 2008). In addition, previous studies reported that cortical responses peaking at 70 ms in S1 to test stimuli were not reduced by preceding stimuli when presented to tactile stimulus paired with an ISI of 0.3 s (Wühle et al, 2010).…”

“…The generation mechanisms of the P35m and P60m components are not fully understood; however, a number of experiments have suggested that P35m and P60m components may at least partly reflect the mechanism of GABAergic inhibitory post synaptic potentials (IPSPs) (Huttunen, 2010;Huttunen et al, 2008;Wikström et al, 1996). Wikström et al (1996) reported that the subsequent P35m and P60m deflections from S1 were sensitive to the ISI by observing the reduction in SEF amplitude for sensory input with higher frequency.…”

Widespread inter-ictal excitability changes in patients with temporal lobe epilepsy: A TMS/MEG study

“…Since all of the recruited patients were medically intractable epilepsy patients, our observation limits our ability to determine whether the widely distributed changes of cortical excitability is affected by different levels of seizure control. It has been reported that PPI phenomenon is associated with GABA receptor mediated circuits (Huttunen et al, 2008;Hsu et al, 2013). Given that the recruited patients were taking multiple AEDs, including carbamazapine, clobazam, topiramate and valproic, which influence functions of GABA receptor, the results should be interpreted cautiously.…”

“…A widely used approach to assess cortical excitability is paired-pulse paradigm, in which two stimuli are presented with a short interstimulus interval (ISI). The response to the second stimulus (R2) is normally smaller than the first one (R1) (Huttunen et al, 2008), this is known as the so-called paired-pulse inhibition (PPI). Using this approach, the balance between cortical excitation and inhibition can be evaluated by measuring the ratio between the strengths of R2 and R1 (R2/R1).…”