Computer simulation of electrocortical activity at millimetric scale.

Abstract

We report a simulation of electrocortical wave activity at millimetric scale, during the "desynchronised" state. Asymmetric sigmoid pulse/wave relations, short-range excitatory/inhibitory interactions and long-range excitatory couplings of pools of cortical cells were modelled. Frequency/wave number analysis of cat electrocorticogram was compared with the results of simulation. Local standing waves, with wave numbers from about 0.25/mm to 3.3/mm independent of temporal frequency, appeared in real and simulated ECoG. These arise from interactions of excitatory and inhibitory cells and reciprocal excitation of pyramidal cells. The simulation also exhibits long wave length activity consistent with that of the real ECoG. Serial relay of excitation gives rise to travelling waves with a velocity of about 0.6 m/sec, which approximates earlier experimental estimates based on coherence. Interaction of the local and travelling waves results in group waves with high phase velocities (32 m/sec at 5 Hz, to 0.6 m/sec at 50 Hz). Such group waves have not yet been experimentally identified and would be readily confused with effects of volume conduction. However, the frequency response characteristics of the simulation, along with the group waves, may account for experimental findings of action potential correlation with local field potentials at 40-50 Hz and long-range synchronisation of action potentials.