Adaptability is an intrinsic characteristic of the human brain, thus, its behaviour modifies according to the different perceived inputs (being these either external or internal). Taking advantage of the previously mentioned, a considerable amount of research has been performed using non-invasive stimulation techniques (transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS)). These methods are powerful tools to explore neuroplastic processes since they are able to produce changes in cortical excitability and consequently modify the physiological activity underlying these processes. The efficacy of the stimulation and the duration of the effects depend on several factors such as the type of stimulation (TMS/tDCS/tACS), stimulation parameters – stimulus intensity, number of pulses and interstimulus intervals –and the brain state before and during stimulation. A large amount of data has been obtained from research where motor cortex (M1) excitability has been assessed. The results from these studies reach a certain level of agreement regarding the effects produced by the different stimulation protocols. However, our current knowledge suffers from a lack of agreement when examining cognitive processes. A major problem with cognitive studies is that the system’s response, i.e. a form of cognition, can usually not be measured as accurately as the EMG signal used in M1 studies. Even when similar methods are employed, results are often contradictory and add to the problem to decide which technique is the most appropriate. Another important and exciting point in cognitive research is the placebo effect which can play a major role in stimulation studies. The goal of the proposed Research Topic is to elucidate the effects of standard stimulation techniques (low/high frequency rTMS, TBS, tDCS and tACS), whose inhibitory and excitatory effects on M1 are well studied, on areas related to cognition such as prefrontal and parietal cortices.

Questions we would like to address in this Research Topic include, but are not limited to the following:

1. Which stimulation protocols are effective in producing changes relevant to cognitive processing? Do these protocols convey inhibitory or excitatory effects? How long do the effects last? Vice versa, which protocols are not suitable for this kind of studies?

2. Can the changes produced by non-invasive stimulation techniques be measured by modalities such as fMRI, MRS, EEG or MEG?

3. Sham stimulation - which protocols are the most adequate to control for placebo effects?
Often, sham protocols involve effective stimulation parameters applied to a brain area which is believed to be irrelevant to the process under observation. It is arguable that this concept can be used in cognitive research as many processes involve distributed cortical networks and “safe” areas are hard to define. Therefore, we are looking forward to contributions addressing this question and analyzing the effects of their sham protocols. Innovative designs and novel placebo techniques are also welcome.Furthermore, we are open to receiving studies performed in M1 with new experimental methods that will provide relevant information about the reliability and efficacy of the different stimulation protocols.

Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.