Neurofeedback Tunes Scale-Free Dynamics in Spontaneous Brain Activity

TL;DR

This study demonstrates that neurofeedback can modulate brain's scale-free dynamics, normalizing abnormal long-range temporal correlations in both healthy and PTSD-affected individuals, with implications for clinical interventions.

Contribution

It shows that neurofeedback can induce self-tuning of brain activity's temporal complexity, reversing abnormal dynamics associated with psychiatric disorders.

Findings

Neurofeedback increased LRTCs in healthy adults.

PTSD patients showed normalization of abnormal LRTCs after NFB.

LRTC strength inversely related to oscillation amplitude.

Abstract

Brain oscillations exhibit long-range temporal correlations (LRTCs), which reflect the regularity of their fluctuations: low values representing more random (decorrelated) while high values more persistent (correlated) dynamics. LRTCs constitute supporting evidence that the brain operates near criticality, a state where neuronal activities are balanced between order and randomness. Here, healthy adults used closed-loop brain training (neurofeedback, NFB) to reduce the amplitude of alpha oscillations, producing a significant increase in spontaneous LRTCs post-training. This effect was reproduced in patients with post-traumatic stress disorder, where abnormally random dynamics were reversed by NFB, correlating with significant improvements in hyperarousal. Notably, regions manifesting abnormally low LRTCs (i.e., excessive randomness) normalized toward healthy population levels, consistent with theoretical predictions about self-organized criticality. Hence, when exposed to appropriate training, spontaneous cortical activity reveals a residual capacity for "self-tuning" its own temporal complexity, despite manifesting the abnormal dynamics seen in individuals with psychiatric disorder. Lastly, we observed an inverse-U relationship between strength of LRTC and oscillation amplitude, suggesting a breakdown of long-range dependence at high/low synchronization extremes, in line with recent computational models. Together, our findings offer a broader mechanistic framework for motivating research and clinical applications of NFB, encompassing disorders with perturbed LRTCs.