The effect of spikes and spike-free epochs on topographic brain maps

Maps of foci, when no discharges nor obvious slow activity were included in the map, usually (84%) showed changes within the focus itself and also in adjacent areas (58%) and often (47%) in the mirror region. An increase in activity was more often seen in the more active foci, especially in the delta and beta 2 ranges, and decrease in activity was usually seen with inactive foci. When discharges were included in the maps, an increasing number was associated with an increase at the main focus in all ranges, especially in delta and beta 1, but much less often in beta 2. The amount of electrical charge required for a change in the map with spikes was approximately 40 nanocoulombs (nC) for the first and second changes, increasing to around 50 nC with adjacent or separate foci. "Artificial" spikes produce more delta activity than other frequency ranges and the FFT of various pulses show maximal amplitudes at the slowest frequencies.