High gamma (HG, 80-150Hz) activity in macroscopic clinical records is considered a marker for critical brain regions involved in seizure initiation and is correlated with pathological multiunit firing during neocortical seizures (Weiss et al., Brain 2013). However, the effects of the seizure’s spatiotemporal dynamics on HG power generation are not well understood.

We studied HG generation and propagation, using a three-step, multi-scale signal analysis and modeling approach. First, we analyzed concurrent neuronal and microscopic network HG activity in neocortical slices from seven intractable epilepsy patients. We found HG activity in these small networks, especially when single neurons displayed paroxysmal depolarization shifts (PDSs). Second, we examined HG activity acquired with microelectrode arrays (MEAs) recorded during human seizures (n=8). We confirmed the presence of synchronized HG power across microelectrode records and HG activity at the macroscale, both specifically associated with the seizure’s core region, i.e. the area that showed multiunit spiking correlated with the seizure activity. Third, we used volume conduction based modeling to relate HG activity and network synchrony at different network scales. We show that local HG oscillations require high levels of synchrony to cross spatial scales and that this requirement is met at the microscopic scale, but not within macroscopic networks. Instead, we present evidence that HG power at the macroscale may result from harmonics of ongoing seizure activity.

We conclude that ictal HG power can be a marker for the seizure core, but generating mechanisms can differ across spatial scales.

Wednesday 24 February 2016, 16:30 - 17:30 h

Building Carré - room CR 3.022