Do Abnormal Sharp Waves Coming from the Hippocampus Disrupt Cognition in Humans?

In the May 17, 2013, journal Neurology articles ahead of press, Drs. Kleen and colleagues from Dartmouth Hitchcock Medical Center,present a fascinating analysis of 10 patients who had depth electrodes implanted in their hippocampus for preoperative seizure localization. The patients were evaluated to see the impact of non seizure discharges on various memory functions. The study found the following.

• Interictal discharges – discharges when one is not seizing-- occurring in the memory retrieval period decreased the likelihood of a correct response when they were on the opposite side to the seizure focus or occurring on both sides.

• Moreover, bilateral discharges during memory maintenance had a similar effect, particularly when spike wave complexes of longer duration occurred.

• Interictal epileptiform discharges during encoding or that time when new information is being recorded has no effect and reaction time was also unaffected by interictal epileptiform discharges.

The authors concluded that hippocampal interictal discharges in humans disrupt memory maintenance and retrieval but not recording new information. The effects of whether the discharge is bilateral or on the opposite side to the seizure location may relate to how your brain compensates in the area of the brain which is not having seizures. The study strengthens the argument that interictal discharges are not as innocent as once thought.