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. 2022 Oct 25;3(4):589-603.
doi: 10.3390/neurosci3040042. eCollection 2022 Dec.

Intraclass Correlation in Paired Associative Stimulation and Metaplasticity

Giuditta Schapira  1 , Justin Chang  1 , Yeun Kim  1 , Jacqueline P Ngo  1 , Choi Deblieck  2 , Valentina Bianco  3 , Dylan J Edwards  4 , Bruce H Dobkin  5 , Allan D Wu  6 , Marco Iacoboni  1   7
Affiliations

Intraclass Correlation in Paired Associative Stimulation and Metaplasticity

Giuditta Schapira et al. NeuroSci. .

Abstract

Paired associative stimulation (PAS) is a widely used noninvasive brain stimulation protocol to assess neural plasticity. Its reproducibility, however, has been rarely tested and with mixed results. With two consecutive studies, we aimed to provide further tests and a more systematic assessment of PAS reproducibility. We measured intraclass correlation coefficients (ICCs)-a widely used tool to assess whether groups of measurements resemble each other-in two PAS studies on healthy volunteers. The first study included five PAS sessions recording 10 MEPS every 10 min for an hour post-PAS. The second study included two PAS sessions recording 50 MEPS at 20 and 50 min post-PAS, based on analyses from the first study. In both studies PAS sessions were spaced one week apart. Within sessions ICC was fair to excellent for both studies, yet between sessions ICC was poor for both studies. We suggest that long term meta-plasticity effects (longer than one week) may interfere with between sessions reproducibility.

Keywords: long-term potentiation; reliability; spike-timing-dependent plasticity; transcranial magnetic stimulation.

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Conflict of interest statement

Conflicts of InterestThe authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Empirical cumulative density functions of (a) total post-PAS MEPs collected per participant and (b) total post-PAS MEPs collected per study. Blue and yellow dots indicate where Studies 1 and 2 fall, respectively, compared to previously published studies. None of the values in the figure include MEPs collected at baseline.
Figure 2
Figure 2
Interaction plot of Study 1. Significant effect of timepoint (F = 6.884, p < 0.0001). No significant session (F(4, 28) = 1.583, p = 0.206, ηp2 = 0.184) or timepoint by session (F(24, 168) = 1.235, p = 0.219, ηp2 = 0.150) interaction.
Figure 3
Figure 3
Interaction plot of Study 2. No significant effect of timepoint (F(1, 7) = 0.691, p = 0.433, ηp2 = 0.090), session (F(1, 7) = 1.134, p = 0.322, ηp2 = 0.139), or interaction between timepoint and session (F(1, 7) = 244, p = 0.636, ηp2 = 0.034). Since only two timepoints were used in Study 2, we opted to graph the results with bar graphs here. Error bars represent standard errors.
Figure 4
Figure 4
Simple linear regression analysis testing the correlation between ICC and CCC in Study 1 (a) and Study 2 (b). Both studies showed significant correlations (Study 1: R2 = 0.97, F(1, 3) = 103.8, p = 0.002), (Study 2: R2 = 0.97, F(1, 3) = 103.8, p = 0.002). In both studies CCC significantly predicted ICC (Study 1: β = 0.5606, p < 0.0001), (Study 2: β = 1.3148, p = 0.002).
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