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. 2022 Jul 12;17(7):e0271311.
doi: 10.1371/journal.pone.0271311. eCollection 2022.

Cerebellar transcranial direct current stimulation disrupts neuroplasticity of intracortical motor circuits

Wei-Yeh Liao  1 , Ryoki Sasaki  1 , John G Semmler  1 , George M Opie  1
Affiliations

Cerebellar transcranial direct current stimulation disrupts neuroplasticity of intracortical motor circuits

Wei-Yeh Liao et al. PLoS One. .

Abstract

While previous research using transcranial magnetic stimulation (TMS) suggest that cerebellum (CB) influences the neuroplastic response of primary motor cortex (M1), the role of different indirect (I) wave inputs in M1 mediating this interaction remains unclear. The aim of this study was therefore to assess how CB influences neuroplasticity of early and late I-wave circuits. 22 young adults (22 ± 2.7 years) participated in 3 sessions in which I-wave periodicity repetitive transcranial magnetic stimulation (iTMS) was applied over M1 during concurrent application of cathodal transcranial direct current stimulation over CB (tDCSCB). In each session, iTMS either targeted early I-waves (1.5 ms interval; iTMS1.5), late I-waves (4.5 ms interval; iTMS4.5), or had no effect (variable interval; iTMSSham). Changes due to the intervention were examined with motor evoked potential (MEP) amplitude using TMS protocols measuring corticospinal excitability (MEP1mV) and the strength of CB-M1 connections (CBI). In addition, we indexed I-wave activity using short-interval intracortical facilitation (SICF) and low-intensity single-pulse TMS applied with posterior-anterior (MEPPA) and anterior-posterior (MEPAP) current directions. Following both active iTMS sessions, there was no change in MEP1mV, CBI or SICF (all P > 0.05), suggesting that tDCSCB broadly disrupted the excitatory response that is normally seen following iTMS. However, although MEPAP also failed to facilitate after the intervention (P > 0.05), MEPPA potentiated following both active iTMS sessions (both P < 0.05). This differential response between current directions could indicate a selective effect of CB on AP-sensitive circuits.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Experimental protocol.
RMT, resting motor threshold; MEP1mV, standard MEP of ~ 1 mV at baseline; CBI, cerebellar-brain inhibition; SICF, short-interval intracortical facilitation; MEPPA, standard MEP of ~ 0.5 mV at baseline with PA orientation; MEPAP, standard MEP of ~ 0.5 mV at baseline with AP orientation; tDCSCB, transcranial direct current stimulation applied to the cerebellum; iTMS, I-wave periodicity repetitive transcranial magnetic stimulation.
Fig 2
Fig 2. Changes in corticospinal excitability during iTMS.
Corticospinal excitability (MEP amplitude) during iTMS1.5 (red circles/bars), iTMS4.5 (blue triangles/bars), and iTMSSham (green squares/bars) are presented as raw values averaged over 10 consecutive MEP trials, resulting in 18 blocks (A), or as the estimated normalised values of the middle and last blocks of 12 consecutive MEP trials, expressed relative to the average response of the first 12 trials. (B). #P < 0.05 session comparison to iTMS1.5. ∧P < 0.05 session comparison to iTMS4.5.
Fig 3
Fig 3. Changes in corticospinal excitability following iTMS1.5 (red), iTMS4.5 (blue), and iTMSSham (green) at 5 and 30 minutes.
Fig 4
Fig 4. Changes in SICF1.5 (A) and SICF4.5 (B) following iTMS1.5 (red), iTMS4.5 (blue), and iTMSSham (green) at 5 and 30 minutes.
Fig 5
Fig 5. Changes in MEPPA (A) and MEPAP (B) following iTMS1.5 (red), iTMS4.5 (blue), and iTMSSham (green).
*P < 0.05.
Fig 6
Fig 6. Changes in CBI following iTMS1.5 (red), iTMS4.5 (blue), and iTMSSham (green) at 5 and 30 minutes.
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