[Paper Review] The Shift in brain-state induced by tDCS: an EEG study

Milena Čukić, Miodrag Stokić+3 more|arXiv (Cornell University)|Dec 4, 2018

Transcranial Magnetic Stimulation StudiesNeuroscience27 references3 citations

TL;DR

This EEG study investigates tDCS-induced shifts in brain-state dynamics using recurrence quantification analysis (RQA) measures—Mean State Shift (MSS) and State Variance (SV)—in 16 healthy subjects. Results show polarity-specific effects: cathodal tDCS significantly reduced MSS compared to anodal stimulation, while SV was only affected by cathodal stimulation, indicating distinct neural state modulation. PCA visualization further revealed separable brain-state patterns post-tDCS, offering new insights into tDCS's neurophysiological impact.

ABSTRACT

Transcranial direct current stimulation (tDCS) is known to have a modulatory effect on neural tissue and that it is polarity specific. It is also shown that tDCS demonstrated the lasting effect in therapeutic applications. The main aim of the study was to examine the effects of tDCS on cortical dynamics by analyzing EEG recordings. We applied here measures taken from Recurrence Quantification Analysis, Mean State Shift (MSS) and State Variance (SV) which were previously used to detect changes in brain-state dynamics after TMS. The studied cohort comprised of 16 healthy subjects; all subjects received anodal and cathodal tDCS, which were given in two separate sessions on the same day. The EEG was recorded from 10 electrodes, positioned over left motor cortex and mirroring right cortex corresponding to 10/20 standard. From three traces of recordings (pre, post1 and post2/before the stimulation, immediately after and 30min after tDCS) we extracted five different intervals (T1-T5) comprising of 500 samples. After calculating MSS and SV on those epochs and statistical testing for a significant difference, we applied Principal Component Analysis (PCA) on the same time series to check whether the data are separable. The results show that tDCS exert polarity specific effects on the MSS as shown by significantly lower MSS values after cathodal stimulation compared to anodal stimulation. Cathodal stimulation affected the SV, as compared to anodal stimulation, which did not lead to detectable changes. We are offering here for the first time an informative PCA visualization of a time-effect of a tDCS stimulation on brain state shift. Further research is needed to elucidate for how long that change can be detected and what neurobiological changes are introduced by that phenomena.

Motivation & Objective

• To examine the effects of transcranial direct current stimulation (tDCS) on cortical dynamics using EEG recordings.
• To assess whether tDCS induces measurable, polarity-specific changes in brain-state dynamics using recurrence quantification analysis (RQA).
• To evaluate the temporal persistence of tDCS-induced brain-state shifts via pre-, post1-, and post2-timepoint recordings.
• To explore data separability and visualization of tDCS effects using Principal Component Analysis (PCA).
• To provide a novel, quantitative framework for detecting tDCS-induced neural state transitions in healthy individuals.

Proposed method

• EEG data were collected from 16 healthy subjects using 10 electrodes over the left and right motor cortices according to the 10-20 system.
• Three EEG epochs were recorded: pre-stimulation, immediately post-stimulation (post1), and 30 minutes post-stimulation (post2).
• Five 500-sample intervals (T1–T5) were extracted from each epoch for analysis.
• Recurrence Quantification Analysis (RQA) was applied to compute Mean State Shift (MSS) and State Variance (SV) as measures of brain-state dynamics.
• Statistical testing was performed to compare MSS and SV values between anodal and cathodal tDCS conditions.
• Principal Component Analysis (PCA) was used to visualize and assess the separability of brain-state patterns across stimulation conditions and time points.

Experimental results

Research questions

• RQ1 Does tDCS induce detectable, polarity-specific changes in brain-state dynamics as measured by MSS and SV?
• RQ2 How do anodal and cathodal tDCS differ in their effects on the stability and variability of neural states?
• RQ3 Can PCA effectively visualize and separate tDCS-induced brain-state shifts over time?
• RQ4 Are the observed tDCS-induced changes in brain-state dynamics persistent 30 minutes after stimulation?
• RQ5 To what extent do the RQA measures MSS and SV reflect the neurophysiological impact of tDCS on cortical activity?

Key findings

• Cathodal tDCS induced a significant reduction in Mean State Shift (MSS) compared to anodal stimulation, indicating a more stable or less variable brain-state transition pattern.
• State Variance (SV) was significantly affected by cathodal stimulation, while anodal stimulation did not produce detectable changes in SV.
• The PCA visualization revealed distinct, separable clusters in brain-state patterns following tDCS, particularly after cathodal stimulation, suggesting a measurable shift in neural dynamics.
• The study demonstrates for the first time that tDCS induces polarity-specific alterations in brain-state dynamics using RQA metrics on EEG data.
• The effects of tDCS on MSS and SV were detectable both immediately after stimulation and 30 minutes post-stimulation, indicating potential persistence of neural state shifts.
• The results suggest that RQA-based measures like MSS and SV are sensitive indicators of tDCS-induced cortical modulation, especially under cathodal stimulation.