Neurofeedback of meditation states to close the loop between subjective experience and brain activity: Evaluating four neural markers

Neurofeedback creates a closed loop between subjective experience and brain activity. Such a feedback loop might allow establishing direct neuro-experiential correspondences, thereby narrowing the gap between the seemingly irreconcilable domains of private conscioussness and external measurement. We introduce a repeated-probing paradigm that allows systematic testing of such neuro-experiential correspondences within individuals by randomizing and blinding the feedback signal direction across trials, combined with semi-structured phenomenological interviews following unblinded regulation sessions. We apply this paradigm to electroencephalography (EEG) neurofeedback in experienced meditators across two studies. Study 1 (n=9) aimed to replicate the previously reported correspondence between posterior cingulate cortex (PCC) gamma activity and effortless awareness, extending the paradigm from visual to auditory feedback. An exploratory Study 2 (n=4) evaluated three additional markers: occipital alpha, midfrontal theta, and PCC high-beta power. In Study 1, participants identified the expected correspondence significantly above chance for both visual and auditory feedback (mean accuracy=72.5%). Additionally, gamma power was significantly reduced during neurofeedback-assisted meditation. In Study 2, no marker yielded significant neuro-experiential correspondences, although alpha power increased and high-beta power decreased during neurofeedback-assisted meditation. Phenomenological interviews revealed distinct meditative strategies, with releasing effort and control predominating in gamma neurofeedback. However, whole-brain and control analyses raised concerns about the spatial specificity and potential muscular contamination of the gamma signal. Our findings introduce a novel neurophenomenological neurofeedback paradigm, replicate and extend previous findings on the correspondence between effortless awareness and gamma feedback, and highlight important limitations in interpreting these effects as reflecting neural rather than muscular activity.