Spreading depression: Evidence of five electroencephalogram phases
Broberg, I Marita
Shuttleworth, C William
Willoughby, John Osborne
MetadataShow full item record
Spreading depression (SD), a self-propagating wave of astroglial and neuronal depolarization, is an accompaniment of several neurological disorders including epilepsy. Its well-described features are initial depolarization followed by EEG flattening. In this in vivo study in awake animals, the relationship of SDs to epileptiform activity was re-examined. We assessed SDs generated by mechanical stimulation and by metabolic inhibition with fluorocitrate. In addition to identifying prolonged EEG depression, we identified two periods, one prior to, and another during depression, characterised by increases in power of specific frequencies that were sometimes associated with epileptiform discharges. The first period, was characterised by ripple activity close to the induction site (88 % of SDs with intracortical electrodes). The second period was characterised by localised low frequency spikes (100 % with dural screw electrodes, 65 % with intra-cortical electrodes). Using fluorocitrate to induce SDs, the initial period was also characterised by runs of spikes (52 %). Finally, with SDs induced by both methods, there was a period at the end of depression when further, unprovoked, SDs occurred (20 %). 5 stages of SD were defined by the above phenomena (in order: excitation, depression, excitation, depression, SD), with metabolic inhibition enhancing the expression of epileptiform spiking.