Heterogeneous Recruitment Curve Responses to Anodal Transcranial Direct Current Stimulation in Children With Unilateral Spastic Cerebral Palsy.
Nicole Metelski, Andrew M Gordon, Shivakeshavan Ratnadurai-Giridharan and 3 others
A single anodal tDCS session produced no significant group-level change in corticospinal excitability in children with unilateral spastic cerebral palsy.
Responses were highly variable: 55% showed a directional shift toward increased excitability, the rest did not. No predictors of response were identified.
Key findings
1The two primary recruitment curve metrics (ΔS50 and slope at inflection) showed no significant group-level change after anodal tDCS.
2All participants completed the protocol with no serious adverse events; 80% reported no symptoms pre- or post-stimulation.
311 of 20 participants (55%) showed a directional leftward shift in S50 following tDCS, indicating a potential increase in corticospinal excitability.
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What it does not show
Single-group design with no sham control: pre/post changes cannot be separated from time-dependent effects, test-retest variability, or TMS-related facilitation. Only one post-tDCS time point (~5 minutes) was assessed, so the temporal profile of any excitability change is unknown. Four children were excluded for insufficient MEPs, which may bias the sample toward those with higher baseline corticospinal excitability. CST subgroups were very small and imbalanced (ipsilateral n = 15, bilateral n = 4, contralateral n = 1), making subgroup comparisons unreliable. No established minimal detectable change or test-retest reliability threshold exists for ΔS50 in children with USCP, so individual 'responder' classifications may reflect measurement error. Ten participants had limited suprathreshold sampling due to the 70% maximum stimulator output safety cap, potentially affecting plateau-dependent parameters. The tDCS was delivered alone; prior evidence suggests effects are more consistent when combined with motor training, which was not part of this protocol.
Declared interests
The authors declared no potential conflicts of interest with respect to the research, authorship, or publication.
The easy way to misread this
Do not read the 55% responder rate as evidence that tDCS works for most children with unilateral spastic CP. The primary outcome was null at the group level, the responder threshold (ΔS50 < 0) is explicitly exploratory with no established minimal detectable change, and the single-group design without a sham condition cannot separate tDCS effects from time-dependent or measurement-related variability.
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