Doctors have long characterized epilepsy as a brain disorder, but researchers at Case Western Reserve University have found that part of the autonomic nervous system functions differently in epilepsy during the absence of seizures. This connection to the involuntary division of the nervous system may have implications for diagnosing and treating the disease and understanding sudden unexpected death in epilepsy (SUDEP). 

The research is published online in the Journal of Neurophysiology.

"All the findings of our study on heart rate variability in epilepsy point to increased activity in the parasympathetic nervous system during sleep," said Roberto Fernández Galán assistant professor of electrical engineering and computer science and senior author of the study. "But we don't know if this abnormality compensates for epilepsy, coincides with the disease or is part of the etiology." 

Specifically, the parasympathetic--or "rest-and-digest"--nervous system modulates breathing and slows the heart rate of sleeping children with epilepsy substantially more than in healthy children. 

To their surprise, the researchers also found that several children who had been diagnosed as neurologically normal--but had similar strong modulation and low heart rates--were later diagnosed with epilepsy. 

The discovery suggests that changes in the parasympathetic tone precede the onset of epilepsy in children.