File:Bcomputaional model in epilepsy figure2b.jpg

Impact of variations in excitatory and inhibitory synaptic strengths (in arbitrary units, AU) on the calculated extracellular activity. The domains of activity patterns in the excitation-inhibition parameter space are shown in left panel of (A), and representative simulated activity patterns in right panel of (A). The arrow indicates the path that was followed to generate the seizure onset activity. Abbreviations: D-desynchronized activity, IB-irregular bursting, O-oscillatory activity, RB-regular burst-firing. A reduction of excitatory coupling strength generates oscillatory network activity that can be viewed in the compound “EEG” signal (B-E). In both (B) and (C), all excitatory connections were reduced in strength. In trace (B) the network contained bursting neurons; in (C) this cell type was absent. In (D) the strength for the synaptic connections between the excitatory populations was selectively reduced; in trace (E) only the strength of the coupling between the excitatory and inhibitory populations was reduced. Comparing traces (D) and (E) with (B), one can see that both connections are critically associated with the network bursts and oscillations observed in trace (B). In both cases, a selective reduction of part of the excitatory system abolishes the oscillatory activity; although, on weakening the excitatory to excitatory connections, some oscillatory activity is retained (D). From Van Drongelen, et al., 2005 with permission (Copyright © 2005 IEEE).