Behavioral State Confounds EEG Biomarkers in Preclinical Rat Studies

Behavioral State Significantly Alters Rat EEG Outcomes

Behavioral activity in rats has a marked impact on electroencephalogram (EEG) power spectra and functional connectivity, as demonstrated by a large 2026 preclinical study (OpenAlex W7216039572). In a sample of 116 waking EEG recordings from freely moving Wistar rats, researchers found that periods of behavioral activity—compared to inactivity—produced robust and region-specific changes in EEG measures across the cortex and subcortical structures. Notably, activity was associated with increased power in the 6-8 Hz and gamma bands, decreased delta and beta power, and differential effects on global functional connectivity (GFC) in gamma and high-gamma frequencies. These findings underscore behavioral state as a critical confound in preclinical neurophysiology, especially when evaluating centrally acting compounds such as psychedelics.

Mechanisms and Context: How Behavioral Activity Modulates EEG

Behavioral activity in rodents—such as locomotion or exploration—induces widespread changes in brain electrical activity, reflected in the EEG power spectrum and connectivity patterns. The 2026 study localized these effects primarily to the parietal and temporal cortices, with additional involvement of the diencephalon and thalamus. Specifically, activity increased 6-8 Hz (theta) and gamma (30-100 Hz) power, while decreasing delta (1-4 Hz) and beta (12-30 Hz) across the cortex. Functional connectivity analyses revealed a nuanced picture: while GFC in the gamma band decreased during activity, high-gamma GFC increased, particularly within thalamic circuits.

These effects are not merely technical artifacts but reflect genuine neurophysiological shifts linked to arousal, movement, and sensory processing. Importantly, the study found that none of the EEG measures were affected in the alpha band (8-12 Hz), suggesting some frequency bands may be more robust to behavioral confounds. This insight is particularly relevant for psychedelic research, where EEG biomarkers are often used to infer drug-induced changes in neural dynamics.

Implications for Preclinical Psychedelic Research and Policy

The discovery that behavioral state can profoundly modulate EEG outcomes has major implications for the design and interpretation of preclinical studies of psychedelics and other centrally acting drugs. Many translational studies rely on EEG biomarkers—such as changes in gamma or theta power—to infer drug effects or mechanisms of action. However, if behavioral activity is not rigorously controlled or reported, apparent drug-induced changes may instead reflect differences in animal movement or arousal, undermining the validity of these biomarkers.

• Standardization is essential: The study highlights the need for standardized protocols to monitor, control, and report behavioral state during EEG acquisition in animal studies. This includes using video tracking, automated behavioral scoring, or restricting recordings to defined behavioral epochs.
• Translational validity at risk: If preclinical EEG biomarkers are confounded by unreported behavioral activity, their relevance to human studies and clinical endpoints is questionable. This may partially explain inconsistencies in the literature and failed translation of some preclinical findings to the clinic.
• Regulatory and funding implications: Agencies such as the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) may increasingly scrutinize the methodological rigor of preclinical neurophysiology data submitted in support of investigational new drug (IND) applications for psychedelics and related compounds.

A non-obvious implication is that some previously published preclinical studies—especially those reporting frequency-specific EEG changes after psychedelic administration—may need to be re-evaluated in light of potential behavioral confounds. This could affect both academic research and industry-sponsored drug development programs.

Risks, Unknowns, and Future Directions

Failure to account for behavioral state in preclinical EEG studies introduces a risk of false positives or negatives regarding drug effects, potentially leading to wasted resources or misleading mechanistic claims. The degree to which behavioral confounds have influenced past psychedelic research is not fully known, as many studies lack detailed behavioral monitoring or reporting.

Key unknowns remain, including whether similar behavioral confounds affect other species (e.g., mice, non-human primates) or how best to standardize behavioral state across diverse experimental paradigms. Additionally, the interaction between drug-induced behavioral changes (such as hyperlocomotion or stereotypy) and EEG outcomes remains an open question. Addressing these gaps will require interdisciplinary collaboration between behavioral neuroscientists, electrophysiologists, and translational researchers.

Looking Ahead: Toward More Reliable Preclinical Biomarkers

Future preclinical studies of psychedelics and other neuroactive compounds should incorporate rigorous behavioral monitoring and transparent reporting of animal state during EEG acquisition. Funding agencies and journals may increasingly require such standards to ensure data reliability and translational relevance. As the field moves toward more sophisticated biomarkers and mechanistic endpoints, integrating behavioral and electrophysiological data will be essential for advancing both basic science and drug development.

How we research: This article was written and reviewed by Dr. Alex M. Greene, PhD (Neuroscience), with reference to the original study published in OpenAlex (W7216039572) on 2026-10-01. Last reviewed: 2026-10-02.