Identifying epileptic foci in patients who are refractory may, in some cases, seem relatively straightforward (eg, mesial temporal lobe epilepsy with hippocampal sclerosis on magnetic resonance imaging). Indeed, across all age groups, the best outcomes following surgical resection occur in patients who have a structural abnormality identified on imaging. In recent years, however, we have learned that residual abnormal network activity following surgery may still allow ongoing seizures, even in those patients with clearly identified epileptic foci. The “ringleader” has been taken out, but the “gang” may still be there. This is an area where advancements in source imaging are needed and are eagerly anticipated. Surgical and nonsurgical applications of source imaging are expected to parallel a better understanding of brain networks (and connectivity) and their role in seizure onset and propagation. While some aspects of source imaging are still investigational and current applications are often limited to specialized epilepsy surgical centers, this technology is also beginning to show promise in other areas.

In contrast to the conventional electroencephalogram (EEG), which may use 22 electrodes, our high-density EEG employs 256 electrodes to produce a high-resolution map. Consider the difference between images from a 0.5-megapixel camera and a 24-megapixel camera. The more data points, the better the picture of seizure origin and spread, which can greatly help to improve surgical decision making or even the planning for vagus nerve stimulation. In the past, computer software was cumbersome and you could spend an entire day on a single patient, but, much akin to what has happened with smartphones, things are changing. High-density EEG and functional imaging techniques can improve functional mapping, which may enable surgeons to avoid damaging the parts of the brain that are involved in speech, motor function, or other critical functions. Beyond surgery, if we can use tools such as high-density EEG to identify changes in brain function that are associated with the initiation of a new epilepsy treatment, that has tremendous potential. If we can actually see that we are restoring a more normal connectivity pattern, that might serve as a biomarker to measure treatment response much more quickly—perhaps even after just a few months of treatment rather than waiting a year.

In summary, the wider application of source imaging outside of the investigational and surgical arenas is anticipated. As epileptic source localization improves, we expect that it will migrate from today’s limited use in epilepsy surgical centers to more widespread use in everyday epilepsy care.