Spontaneous thought orientation tracked by fMRI networks and EEG alpha power dynamics
Tomas Hampejs, David Tomecek, Stanislav Jiricek, Vlastimil Koudelka, Lucia Jajcay, Dante Mantini, Jaroslav Hlinka
bioRxiv Preprint Server October 31, 2025 preprint DOI: 10.1101/2025.10.31.684884 via bioRxiv
Summary
Spontaneous, naturally occurring thoughts have distinct brain signatures that can be detected with combined fMRI and EEG recordings. Using machine learning on 240 samples from eight participants, internally versus externally oriented experiences were distinguished with 65.4% accuracy by fMRI and 62.5% by EEG. Externally oriented states involved greater activity in salience, auditory, and visuospatial brain networks and lower occipital alpha power, while internally oriented states showed the opposite pattern, extending prior accounts focused on the default mode network. Across modalities, alpha power correlated negatively with BOLD fluctuations in parietal and occipital regions, indicating that coordinated large-scale network dynamics and alpha oscillations track the natural alternation between inward and outward focus.
Study at a glance
| Characteristics | Observational study combining simultaneous fMRI-EEG with Descriptive Experience Sampling |
|---|---|
| Sample size | 8 |
| Population | Human participants |
| Key finding | Internally and externally oriented spontaneous experiences have distinct neural signatures involving salience, auditory, visuospatial, and default mode networks, with opposite patterns of occipital alpha power. |
Abstract
Understanding how spontaneous, rather than experimentally induced, thoughts relate to brain activity remains a major challenge. We combined simultaneous fMRI and EEG recordings with Descriptive Experience Sampling (DES) to link momentary, naturally occurring experiences to their neural signatures during rest. Using machine-learning classification of 240 time-locked samples from eight participants—each completing nine 25-minute resting-state sessions—we reliably distinguished internally from externally oriented experiences (fMRI accuracy = 65.4%, EEG = 62.5%). Externally oriented states showed greater fMRI activity in salience, auditory, and visuospatial networks and lower occipital alpha power in EEG, whereas internally oriented states exhibited the opposite pattern, extending prior DMN-focused accounts of internally directed states. Across modalities, integrated resting-state alpha power correlated negatively with BOLD fluctuations in parietal and occipital regions. These multimodal findings reveal distinct neural signatures of spontaneous experience and demonstrate that coordinated large-scale network dynamics and alpha-band oscillations track the natural alternation between inward and outward focus in the human mind.