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More focal is not always better: effects of conventional versus high-definition transcranial direct-current stimulation on implicit motor sequence learning
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  • Mahyar Firouzi,
  • Kris Baetens,
  • Manon Saeys,
  • Catalina Duta,
  • Chris Baeken,
  • Frank Van Overwalle,
  • Eva Swinnen,
  • Natacha Deroost
Mahyar Firouzi
Vrije Universiteit Brussel

Corresponding Author:[email protected]

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Kris Baetens
Vrije Universiteit Brussel
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Manon Saeys
Vrije Universiteit Brussel
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Catalina Duta
Vrije Universiteit Brussel
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Chris Baeken
Vrije Universiteit Brussel
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Frank Van Overwalle
Vrije Universiteit Brussel
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Eva Swinnen
Vrije Universiteit Brussel
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Natacha Deroost
Vrije Universiteit Brussel
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Abstract

Conventional transcranial direct-current stimulation (tDCS) delivered to the primary motor cortex (M1) has been shown to enhance implicit motor sequence learning (IMSL). Conventional tDCS targets M1 but also the motor association cortices (MAC), making the precise contribution of M1 to IMSL presently unclear. We aimed to address the roles of these areas by comparing conventional tDCS of M1 and MAC to High-Definition (HD) tDCS, which more focally targets M1. In this sham-controlled, crossover study in 89 healthy adults, we used mixed-effects models to analyze sequence-specific and general learning effects in the acquisition, short- and long-term consolidation phases of IMSL, as measured by the serial reaction time task. Conventional tDCS did not influence general learning, improved sequence-specific learning during acquisition (anodal: M=42.64 ms, sham: M=32.87 ms, p=.041) and deteriorated it at long-term consolidation (anodal: M=75.37 ms, sham: M=86.63 ms, p=.019). HD tDCS did not influence general learning, slowed performance specifically in sequential blocks across all learning phases (all p’s<.050), and consequently deteriorated sequence-specific learning during acquisition (anodal: M=24.13 ms, sham: M=35.67 ms, p=.014) and long-term consolidation (anodal: M=60.03 ms, sham: M=75.01 ms, p=.002). Our findings indicate that generalized stimulation of M1 and MAC enhanced acquisition, but hindered consolidation of IMSL. In contrast, focal M1 stimulation by HD tDCS worsened overall performance, likely due to cathodal inhibition of MAC as induced by the return electrodes. Consequently, this disruption of performance supports the notion that these areas fundamentally contribute to IMSL as an integral part in the cortico-basal ganglia-thalamo-cortical network.
06 Apr 2023Submitted to European Journal of Neuroscience
07 Apr 2023Submission Checks Completed
07 Apr 2023Assigned to Editor
07 Apr 2023Review(s) Completed, Editorial Evaluation Pending
16 Apr 2023Reviewer(s) Assigned
01 May 2023Editorial Decision: Revise Major
14 Jul 20231st Revision Received
14 Jul 2023Submission Checks Completed
14 Jul 2023Assigned to Editor
14 Jul 2023Review(s) Completed, Editorial Evaluation Pending
14 Jul 2023Reviewer(s) Assigned
14 Sep 2023Editorial Decision: Revise Major
29 Sep 20232nd Revision Received
03 Oct 2023Submission Checks Completed
03 Oct 2023Assigned to Editor
03 Oct 2023Review(s) Completed, Editorial Evaluation Pending
04 Oct 2023Editorial Decision: Accept