Abstracts

Rationale: Despite remarkable progress in non-invasive investigations, some patients with intractable epilepsy require intracranial recording to lateralize or precisely localize the epileptic generator to assess candidacy for seizure surgery. The most widely used technique at our institution involves the stereotactic placement of intracranial-intracerebral (aka depth ) electrodes. They are well tolerated with very low morbidity and yield excellent high-quality recording. Traditionally, we have used so-called macro-contacts but have more recent experience with altering the contact size. While the original goal of this examination was the observation of high-frequency oscillations, one could also assess for the possibility of single-unit recording. Methods: In order to record from both single-units and clinical EEG, specialized recording equipment is necessary. Funding for this device as well as ongoing costs of electrodes, cables and connectors may be a limiting factor to the dissemination of this technique. Results: What is to be gained however is the opportunity to explore basic mechanisms of epileptogenesis at the level of the single-unit and to understand how these findings might relate to data from larger populations of cells (eg. EEG/SEEG). Also, clinician-researchers interested in cognitive neuropsychology may exploit this unique and perhaps temporary window of opportunity in the awake and behaving human patient. Conclusions: Several centres have reported stable single-unit recording for up to a week after implantation with intracranial electrodes with no additional morbidity. The two main technical approaches reported include reducing the size of contacts along the shaft of the electrode and introducing micro-wires through its hollow lumen. Commercial electrodes are available for each of these designs. Here we evaluate each type in terms of cost, technique of implantation, quality of recording and MRI compatibility.