Fundamental Technology

Electroencephalography (EEG) records electrical brain activity through electrodes placed on the scalp, the oldest neurophysiological recording method with roots in 1920s research. EEG captures voltage fluctuations reflecting coordinated population neural activity across entire brain regions, recording from relatively distant neural sources through the intervening scalp, skull, and cerebrospinal fluid.

Advantages and Limitations

EEG is completely noninvasive with zero surgical risk, enabling research and application in any population without medical contraindication. However, spatial resolution is severely limited, with electrodes capturing blurred summations of activity from large brain volumes. Signal quality is substantially lower than intracortical or surface electrode approaches, limiting decoding accuracy.

Consumer and Research Applications

EEG dominates consumer BCI applications, including meditation apps, gaming interfaces, and attention monitoring systems. Research laboratories use EEG for large-scale population studies and longitudinal investigations spanning years or decades.

Signal Characteristics

EEG measures oscillatory rhythms in specific frequency bands including alpha (8-12 Hz), beta (12-30 Hz), and gamma (30-100 Hz) activity. BCIs often decode intended movement or attention through modulation of sensorimotor rhythms, rather than direct neural population decoding as achieved through higher-resolution approaches.

Comparison to Invasive Methods

While EEG performs poorly compared to intracortical or endovascular approaches for communication BCIs, the complete absence of surgical risk makes EEG valuable for specific applications where perfect decoding accuracy is unnecessary. Recent advances in signal processing have marginally improved EEG BCI performance, though fundamental physical limitations persist.