Source:Clinical Neurophysiology, Volume 128, Issue 3
Author(s): G. Koch
Transcranial magnetic stimulation (TMS) provides a unique opportunity to test the causal neurophysiological interactions between interconnnected brain areas. This can be done by applying two coils over two different brain areas and deliver subsequent TMS pulses with a certain time interval in the range of few milliseconds (dual-site TMS). In these paradigms, a conditioning stimulus (CS) is first used to activate putative pathways to the motor cortex (M1) from the site of stimulation, while a second, test stimulus (TS), delivered a few ms later probes any changes in excitability that are produced by the input. Dual-site TMS can be used to investigate mechanisms of spike timing dependent plasticity within a certain network. LTP- and LTD-like effects can be induced in M1 following the repeated application of paired pulses over interconnected areas such as contralateral M1, ventral premotor cortex, supplementary motor area or the posterior parietal cortex (PPC). A crucial question is whether dual site TMS effects are limited to M1 or can be used to measure the activity of the other targeted non motor areas. The combination of dual site TMS with electroencephalography (EEG) is a promosing way to overcome these issues (Veniero et al., 2013; Picazio et al., 2014). TMS/EEG allows to measure physiological signals generated at the cortical level by TMS, including those generated in the so-called silent-areas such as PPC and to assess modifications of cortical connectivity.
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