A practical procedure for real-time functional mapping of eloquent cortex using electrocorticographic signals in humans

Abstract

Functional mapping of eloquent cortex is often necessary prior to invasive brain surgery, but current techniques that derive this mapping have important limitations. In this article, we demonstrate the first comprehensive evaluation of a rapid, robust, and practical mapping system that uses passive recordings of electrocorticographic signals. This mapping procedure is based on the BCI2000 and SIGFRIED technologies that we have been developing over the past several years. In our study, we evaluated 10 patients with epilepsy from four different institutions and compared the results of our procedure with the results derived using electrical cortical stimulation (ECS) mapping. The results show that our procedure derives a functional motor cortical map in only a few minutes. They also show a substantial concurrence with the results derived using ECS mapping. Specifically, compared with ECS maps, a next-neighbor evaluation showed no false negatives, and only 0.46 and 1.10% false positives for hand and tongue maps, respectively. In summary, we demonstrate the first comprehensive evaluation of a practical and robust mapping procedure that could become a new tool for planning of invasive brain surgeries.

Figures

Figure 1

Example for ECoG signal changes between the tasks of repetitively opening and closing of the hand and resting. (A) Signals in the mu/beta band (5-30 Hz) decrease with the task and are spatially less specific (lower topography), whereas signals in the gamma band (70-116 Hz) increase with the task and are spatially more specific (upper topography). (B) The power spectrum on a logarithmic scale for the electrode market with a star in the topographies illustrates the spectral decrease in the mu/beta band (marked by the green bar) and spectral increase in the gamma band (orange bar).

Figure 2

Example of an implanted subdural grid in patient AMC3. (A) Subdural grid placed over fronto-parietal areas. (B) Lateral radiograph indicating the position of the grid.

Figure 3

SIGFRIED-based mapping procedure: After an initial 6 min baseline period, an automated routine generates a statistical signal model for that baseline period for each electrode (this automated procedure takes less than one min). The subject then alternated between hand and tongue movement tasks interspersed with rest periods.

Figure 4

Output of the SIGFRIED procedure for two locations recorded from subject VAH2. Locations for hand (top) and tongue (bottom) electrode are each marked in Fig. 7 by a star and rectangle, respectively.

Figure 5

Equipment setup and interface to the investigator. The subject is presented with visual cues shown on a computer monitor while electrocorticographic signals are recorded. Both the patient screen and the data acquisition device are interfaced with a laptop computer running BCI2000. BCI2000 acquires signals from the device, submits these signals in real time to the SIGFRIED method, and presents the results visually in a topographical display to the investigator.

Figure 6

Results of electrical cortical stimulation (left) and the passive functional mapping using SIGFRIED (right) for subjects AMC1 to AMC5. Lateral radiographs (left) show the results of the electrical cortical stimulation for hand (yellow) and tongue (red) and no response to hand or tongue (white). Transparent circles indicate no stimulation. Detailed lateral radiographs (right) show the result of the passive functional mapping using SIGFRIED after 30, 60, 120 and 180 seconds for hand (yellow) and tongue (red). The number indicates the final maximum r2 between the stimulus and the SIGFRIED response (0 to 1).

Figure 7

Results of electrical cortical stimulation (left) and the passive functional mapping using SIGFRIED (right) for subjects VAH1, VAH2, UMC1, UMC2 and BJH1. Lateral radiographs or computer tomographic renderings (left) show the results of the electrical cortical stimulation for hand (yellow) and tongue (red) and no response to hand or tongue (white). Transparent circles indicate no stimulation. Detailed lateral radiographs (right) show the result of the passive functional mapping using SIGFRIED after 30, 60, 120 and 180 seconds for hand (yellow) and tongue (red). The number indicates the final maximum r2 between the stimulus and the SIGFRIED response (0 to 1). The real-time SIGFRIED traces in Fig.4 are for the locations marked by a yellow star and red rectangle in subject VAH2, respectively.