Do ictal slow waves correlate with forgetting?

Many patients with epilepsy suffer from memory dysfunction. Are the seizures the reason for poor memory function? Studies investigating the long-term impact of seizures on memory conclude that in most epilepsy syndromes it is unlikely that memory performance gets worse over time. But there is an exception: Frequently occurring seizures of a specific form, so-called clonic-tonic seizures, over a long interval of time are likely to damage the patient`s brain. In addition, patients with seizures originating in the left part of the brain showed increased forgetting of contents when a seizure occurred between learning and recall. Slow brain activity correlates with loss of consciousness during epileptic seizures but also with disturbed memory functions in seizures without loss of consciousness. We think that slow activity during and after epileptic seizures could be a correlate of a disturbing mechanism in the consolidation of memory entries. To test this assumption, we need to control for other factors which could jeopardize or sustain memory processes, such as the beneficial effect of sleep on memory, epileptiform events that occur between seizures, and mechanisms that occur during encoding, consolidation, or retrieval of memory entries. Controlling these and other factors is possible in a video-EEG-monitoring unit, where patients are observed and evaluated for a week on 24 hours per day. We will assess 100 patients with surface recordings of electric brain activity (the electroencephalogram, EEG) and 20 patients with invasive recordings (i.e., electrodes implanted into the patient`s brain) by a schedule of 6 repeated memory tests including 3 days and 3 nights. We will test if properties extracted from the EEG during and between the eventually occurred seizures are related to memory performance. The results of this study are not only relevant for each patient`s perspective on the impact of the seizures on cognition. The results could also serve as a justification for therapies and incubate new theories about the relationship between memory consolidation and states of unconsciousness such as seizures or sleep.

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