Quadratic dose-response relationship between caffeine (1,3,7-trimethylxanthine) and EEG correlation dimension

Area of Science:

• Neuroscience
• Cognitive Science
• Psychopharmacology

Background:

• Previous research has not established a clear dose-response link between caffeine and EEG power spectra across cognitive tasks.
• EEG signal complexity, measured by correlation dimension (D2), offers a nonlinear approach to analyze brain dynamics.
• The study design aimed to minimize bias against detecting dose-response relationships, even nonlinear ones.

Purpose of the Study:

• To investigate a consistent dose-response relationship between oral caffeine intake and EEG D2.
• To examine this relationship across six different caffeine doses and four cognitive tasks.
• To compare caffeine's effect on EEG D2 with placebo conditions within subjects.

Main Methods:

• A within-subjects design with 10 participants, involving experimental (caffeine) and placebo conditions.
• EEG D2 was measured from frontal and central scalp locations (Fz, F3, F4, Cz) across varying caffeine levels (100-600 mg) and cognitive tasks.
• Statistical analysis included a three-way interaction test and regression analyses to assess linear and quadratic trends.

Main Results:

• A significant three-way interaction between caffeine, dose, and cognitive task was observed (P = 0.001).
• Placebo conditions showed a linear trend in EEG D2 (average R2 = 0.54).
• Caffeine significantly enhanced the explanatory power of trends, with linear+quadratic models explaining 30% of variance compared to 0.01% for linear fits, indicating a robust quadratic dose-response relationship.

Conclusions:

• Caffeine demonstrates a robust quadratic dose-response relationship with EEG signal complexity (D2) across cognitive tasks.
• This contrasts with the linear trends observed under placebo conditions.
• Findings have implications for understanding caffeine's impact on brain dynamics and highlight the utility of nonlinear EEG analysis.