Dense-Array Electroencephalography with Source Imaging Gives a New View into Epilepsy

Dense-Array Electroencephalography with Source Imaging Gives a New View into Epilepsy

MINNEAPOLIS / ST. PAUL (08/24/2012) —A team of University of Minnesota biomedical engineers and researchers from Mayo Clinic published a groundbreaking study today that outlines how a new type of non-invasive brain scan taken immediately after a seizure gives additional insight into possible causes and treatments for epilepsy patients. The new findings could specifically benefit millions of people who are unable to control their epilepsy with medication.

The research was published online today in Brain, a leading international journal of neurology.

Temporal lobe seizures have a significant chance to induce impairment of normal brain functions. Even after the termination of ictal discharges, during the post-ictal period, loss of consciousness, decreased responsiveness or other cognitive dysfunctions can persist. Previous studies have found various anatomical and functional abnormalities accompanying temporal lobe seizures, including an abnormal elevation of cortical slow waves. Intracranial electroencephalography studies have shown a prominent increase of lower frequency components during and following seizures that impair (complex partial seizures) but not those that preserve (simple partial seizures) normal consciousness and responsiveness. However, due to the limited spatial coverage of intracranial electroencephalography, the investigation of cortical slow waves cannot be easily extended to the whole brain. In this study, we used scalp electroencephalography to study the spectral features and spatial distribution of post-ictal slow waves with comprehensive spatial coverage. We studied simple partial, complex partial and secondarily generalized seizures in 28 patients with temporal lobe seizures. We used dense-array electroencephalography and source imaging to reconstruct the post-ictal slow-wave distribution. In the studied cohort, we found that a ‘global’ spectral power shift to lower frequencies accompanied the increased severity of seizures. The delta spectral power relative to higher frequency bands was highest for secondarily generalized seizures, followed by complex partial seizures and lastly simple partial seizures. In addition to this ‘global’ spectral shift, we found a ‘regional’ spatial shift in slow-wave activity. Secondarily generalized seizures and complex partial seizures exhibited increased slow waves distributed to frontal areas with spread to contralateral temporal and parietal regions than in simple partial seizures. These results revealed that a widespread cortical network including temporal and fronto-parietal cortex is involved in abnormal slow-wave activity following temporal lobe seizures. The differential spectral and spatial shifts of post-ictal electroencephalography activity in simple partial, complex partial and secondarily generalized seizures suggest a possible connection between cortical slow waves and behavioural and cognitive changes in a human epilepsy model.

Epileptic seizures have mystified people for thousands of years, appearing in the Bible numerous times as evidence of wicked spirits invading innocent human hosts. Though Jesus reportedly treated these cases with divine intervention, he failed to leave clinical guidelines, leaving modern clinicians to continue to be confounded by epilepsy.

An important factor when deciding what treatment option to offer an individual patient is knowing where in the brain the electrical storm is generated. Commonly EEG is used when a patient is experiencing a seizure to do this localization, but now researchers from University of Minnesota and Mayo Clinic have shown that a high density EEG test immediately following a seizure offers similar ability. They used an EEG array of 76 electrodes (more than double the 32 usually used) to study 28 epileptic patients and discovered that the frontal lobe is a predominant source of the seizure during particularly severe episodes. The researchers hope the new technology will be adopted to help individual patients address the unique nature of their disease.

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