PHILADELPHIA—Patients who have seizures at night tend to have worse memory than patients with other types of epilepsy, according to data presented at the 69th Annual Meeting of the American Epilepsy Society.
Many patients with epilepsy have cognitive deficits that decrease their quality of life. Research in healthy participants has shown that new information is more readily committed to memory after a night of sleep than after an equivalent period of daytime wakefulness. It is unclear, however, whether memory processing is altered in patients with epilepsy.
Rani Sarkis, MD, a neurologist at Brigham and Women’s Hospital in Boston, and colleagues prospectively recruited 11 patients with epilepsy from the adult epilepsy monitoring unit at their hospital. Eligible participants were between ages 18 and 60 and had a diagnosis of focal-onset seizures. Patients with a prior craniotomy, barbiturate or benzodiazepine use, or substance abuse were excluded.
Participants were trained on a memory task that consisted of 15 pairs of colored pictures of animals and objects on a 5 × 6 grid. The participants were repeatedly shown the picture-pair locations until they could recall at least 40% of the items. At an average of 12 hours later, patients were tested on the material that they had trained on, and then they were trained on another set of pictures. Patients were trained and tested every 12 hours until they had a seizure, were sleep deprived, or after four days if no seizure occurred. The researchers placed EMG chin electrodes on the participants to enable sleep scoring. They assessed the number and density of sleep spindles using a wavelet-based algorithm.
Three participants had seizures during the day, and another three had nocturnal seizures. The percentage of memory retention over 12 hours of wakefulness was 62.7%. The percentage of memory retention over 12 hours that included sleep was 84.6%. Patients’ average time in stage I sleep was 14%, average time in stage II sleep was 63%, average time in REM was 15%, and average time in slow wave sleep was 8%. Total spindle counts ranged between 170 and 506, and spindle density during stage II sleep ranged between 0.77 and 1.88 spindles per minute.
Performance on overnight testing correlated best with the duration of slow wave sleep in minutes, but did not correlate with total number of sleep spindles or spindle density. The three subjects who had seizures during the day did not have a change in memory retention rates, while the three subjects who had nocturnal seizures had a drop in retention from an average of 92% to 60.5%.
“Our preliminary results show that patients with nocturnal seizures perform worse on memory tasks, suggesting that seizures may interfere with the important memory consolidation processes that unfold during sleep,” said Dr. Sarkis. “Larger prospective studies are needed to confirm these findings,” he added.
—Erik Greb
