Abstracts

Rationale: Localization of cortical function is performed prior to excision of mass lesions adjacent to eloquent cortex or surgery for intractable epilepsy. This localization is typically accomplished by subdural electrical cortical stimulation (ECS) (Penfield and Rasmussen, 1950; Ojemann et al., 1989). This localization method has significant limitations: it is time-consuming, carries the risk of after discharges and the results may not be always be correct (Ojemann et al. 1993). Methods: Recent studies have shown that offline analyses using passive recordings of electrocorticographic activity (ECoG) can detect task-related signal changes (Crone et al. 1998, 2000, 2001; Aoki et al. 1991; Ojemann 1999, 2001; Graimann et al. 2002; Sinai et al. 2005; Miller et al. 2007; Leuthardt et al. 2007) and that these changes are congruent to those detected using fMRI (Lachaux et al. 2007). While the exact relationship between passive ECoG-based mapping and conventional ECS-based mapping is not yet clear, it is likely that passive mapping may supplement or even replace traditional ECS-based mapping methodologies. We have recently described a novel signal processing and visualization method called SIGFRIED (SIGnal modeling For Realtime Identification and Event Detection) (Schalk et al., 2008) that uses passively recorded ECoG activity to detect task-related activity in real time. Results: We have since implemented the SIGFRIED algorithm in the BCI2000 package (Schalk et al., 2004). In this study, we have used this software package to map cortical areas related to hand and tongue movements in nine subjects using ECoG signals. The acquisition of interpretable averaged topographic findings took 30 seconds to three minutes. The location of the identified signal changes was consistent with the results reported in recent offline ECoG mapping studies (Miller et al., 2007, Leuthardt et al., 2007). They were also in general agreement with those achieved using ECS-based mapping in the same patients, which typically took several hours to acquire. Conclusions: In sum, the SIGFRIED/BCI2000 package can be used to rapidly localize cortical function using subdural recordings preparatory to epilepsy surgery. We propose that this information is a useful addition to, or may even become a replacement for, conventional ECS-based localization of cortical function.