Assessing whole-cortex excitability from electromagnetic brain signals

Cortical excitability is a core feature of brain function shaped by microcircuitry, large-scale networks, and neurochemistry. In humans, it can be inferred from indirect electrophysiological measures, yet it remains unclear whether these capture a single construct or multiple processes. We systematically compared established excitability metrics using whole-head magneto-encephalography (MEG) recorded at rest and during 40 Hz auditory stimulation in a large sample of healthy adults. These measures included stimulus-driven synchronization, spectral power, aperiodic (1/f) activity, signal complexity, long-range temporal correlations, and phase–gamma synchronization. Hierarchical clustering identified six distinct excitability dimensions with limited redundancy, indicating that cortical excitability is inherently multidimensional. Aperiodic and alpha-band measures were strongly coupled and most spatially aligned with stimulus responses, while temporal, complexity, and synchronization metrics were largely independent. Regional differences were most pronounced in integrative and internally oriented areas. Each dimension also related differently to cortical morphology and neurotransmitter receptor density, highlighting diverse neurobiological substrates and supporting multimodal approaches to studying excitability.