Abstracts

Rationale: Human brain oscillations span a range of spatiotemporal scales. The spatial organization of neuronal assemblies range from small neuronal clusters to centimeter scale networks. Similarly, the frequencies span a wide range from DC to high frequency oscillations. Methods: We studied 10 patients with hybrid electrodes containing microwires and macroelectrodes. The EEG was acquired using a DC capable broadband amplifier (Neuralynx Inc.).Results: Broadband recordings demonstrated oscillations extending from DC to 700 Hz. Slow oscillations and DC fluctuations were often spatially diffuse, but also occurred in sub-millimeter regions within the seizure onset zone. Fast oscillations (>80 Hz) were primarily localized, and most prominent within the seizure onset zone. In the seizure onset zone frequent sub-millimeter domain seizures were recorded (microseizures) on the microwires, but not on clinical macroelectrodes. The microseizure activity was spatially and temporally correlated with large-scale clinical seizure activity.Conclusions: Multiscale EEG recordings demonstrate oscillations and seizures occur over a range of spatiotemporal scales. The microwires demonstrate independent microdomains of seizure activity occurring throughout the epileptogenic zone. Remarkably, microseizures are not detected with standard macroelectrodes. We propose that the generation of focal seizures may occur by the coalescence of microseizure islands, and only become apparent on macroelectrodes after sufficient tissue has been recruited.