Spatial-temporal patterns of electrocorticographic spectral changes during midazolam sedation

To better understand 'when' and 'where' wideband electrophysiological signals are altered by sedation.

We generated animation movies showing electrocorticography (ECoG) amplitudes at eight spectral frequency bands across 1.0-116 Hz, every 0.1s, on three-dimensional surface images of 10 children who underwent epilepsy surgery. We measured the onset, intensity, and variance of each band amplitude change at given nonepileptic regions separately from those at affected regions. We also determined the presence of differential ECoG changes depending on the brain anatomy.

Within 20s following injection of midazolam, beta (16-31.5 Hz) and sigma (12-15.5 Hz) activities began to be multifocally augmented with increased variance in amplitude at each site. Beta-sigma augmentation was most prominent within the association neocortex. Augmentation of low-delta activity (1.0-1.5 Hz) was relatively modest and confined to the somatosensory-motor region. Conversely, injection of midazolam induced attenuation of theta (4.0-7.5 Hz) and high-gamma (64-116 Hz) activities.

Our observations support the notion that augmentation beta-sigma and delta activities reflects cortical deactivation or inactivation, whereas theta and high-gamma activities contribute to maintenance of consciousness. The effects of midazolam on the dynamics of cortical oscillations differed across regions.

Sedation, at least partially, reflects a multi-local phenomenon at the cortical level rather than global brain alteration homogeneously driven by the common central control structure.