Epileptic spikes propagate from the cortex to the thalamus, with spikes tending to propagate to the thalamus more often in patients with sleep activated spikes (SWAS) and most in patients with epileptic encephalopathy (EE-SWAS). (see first figure below)
In patients with severe cognitive dysfunction, thalamic spikes reduced spindles for 30 seconds and decreased overall spindle rate. See below for an example sweep of data showing the reduction of thalamic spindle occurrence from spikes. (see second image below)
Findings show how slow oscillations can facilitate both epileptic spikes and sleep spindles, which can lead to them looking correlated.