Optical imaging of epileptiform activity in human neocortex.

The surgical outcomes of patients suffering from neocortical epilepsy are not as successful as the surgical outcomes from resections of epilepsy patients with mesial temporal sclerosis. The main difficulty in the treatment of neocortical epilepsy is that current technology has limited accuracy in mapping neocortical epileptogenic tissue. It is known that the optical spectroscopic properties of brain tissue are correlated with changes in neuronal activity. The method of mapping these activity-evoked optical changes is known as imaging of intrinsic optical signals (IIOS). Activity-evoked optical changes measured in neocortex are generated by changes in cerebral hemodynamics (i.e., changes in blood oxygenation and blood volume). Our experimental approach was to acquire high-resolution IIOS maps of epileptiform activity in patients undergoing surgery for medically intractable neocortical epilepsy. Both spontaneous and stimulation-evoked epileptiform activity was monitored. Imaging of intrinsic optical signals was able to localize neocortical epileptic foci precisely by using changes in blood volume in contrast to changes in blood oxygenation. IIOS has the potential to translate from a purely research tool to a new intraoperative approach for the surgical treatment of neocortical epilepsy.