Abstract
Repeated pairing of transcranial magnetic stimulation (TMS) over left and right primary motor cortex (M1), at intensities sufficient to generate descending volleys, produces sustained increases in corticospinal excitability. In other paired associative stimulation (PAS) protocols, in which peripheral afferent stimulation is the first element, changes in corticospinal excitability achieved when the second stimulus consists of brief bursts of transcranial alternating current stimulation (tACS), are comparable to those obtained if TMS is used instead (McNickle and Carson 2015). The present aim was to determine whether associative effects are induced when the first stimulus of a cortico-cortical pair is tACS, or alternatively subthreshold TMS. Bursts of tACS (500 ms; 140 Hz; 1 mA) were associated (180 stimulus pairs) with single magnetic stimuli (120% resting motor threshold rMT) delivered over the opposite (left) M1. The tACS ended 6 ms prior to the TMS. In a separate condition, TMS (55% rMT) was delivered to right M1 6 ms before (120% rMT) TMS was applied over left M1. In a sham condition, TMS (120% rMT) was delivered to left M1 only. The limitations of null hypothesis significance testing are well documented. We therefore employed Bayes factors to assess evidence in support of experimental hypotheses—defined precisely in terms of predicted effect sizes, that these two novel variants of PAS increase corticospinal excitability. Although both interventions induced sustained (~ 20–30 min) increases in corticospinal excitability, the evidence in support of the experimental hypotheses (over specified alternatives) was generally greater for the paired TMS-TMS than the tACS-TMS conditions.
Highlights
In the period since the first utilisation of the technique, paired associative stimulation (PAS) has become a method of choice with which to investigate the expression of neuralCommunicated by Francesco Lacquaniti.In assessing the effects of PAS on corticospinal excitability, as for many other forms of non-invasive brain stimulation1 3 Vol.:(0123456789)Experimental Brain Research (2021) 239:21–30(NIBS), it has been customary to rely upon null hypothesis significance testing (NHST)
The Bayes factor is a likelihood ratio that expresses the degree to which the data support the experimental hypothesis over the null
Each experimental hypothesis was defined quantitatively—in terms of an effect size range, on the basis of previous research (Table 1). It is considered both a strength and weakness of the Bayesian approach that each person can have their own sense of how the odds represented by a Bayes factor should be interpreted
Summary
(NIBS), it has been customary to rely upon null hypothesis significance testing (NHST) This approach is used to establish whether, on the basis of the observed data, the null-hypothesis of no effect can be rejected. Models and parameters that exhibit poor levels of prediction suffer a consequential decline in plausibility (Wagenmakers et al 2016) It has been proposed previously (de Graaf and Sack 2018) that with respect to NIBS, Bayesian methods may be used to help formalize the inferences drawn on the basis of null results. We take the further step of using Bayes factors to assess the evidence in support of specific experimental hypotheses—concerning two types of PAS, which are defined quantitatively in terms of predicted effect sizes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
