Figure 1.
Average fronto-posterior Granger Causality patterns.
Maroon line: posterior→frontal direction. Blue line: frontal→posterior direction. GC between (a) left frontal – left posterior, (b) right frontal – left posterior, (c) left frontal – right posterior; (d) right frontal – right posterior. Shaded areas: mean GC ± standard deviation. An increase in fronto→posterior GC after anesthesia induction is observed. Vertical lines indicate anesthetic induction (AI) and recovery of consciousness (ROC). As expected, the fronto→posterior GC returns to baseline at recovery of consciousness. Subjects with no GC over the right posterior area due to bad electrode contact were excluded from the average (2 patients). X-axis in arbitrary samples.
Figure 2.
Patient-wise average GC values ± standard deviation (error bars).
50-second segments of ‘Awake’ (pre-LOC, post-ROC) and ‘Anesthetized’ (mean GC for post-LOC and pre-ROC) states. (a) GCLF→LP, (b) GCRF→LP, (c) GCLF→RP, and (d) GCRF→RP. The differences in GC between ‘Awake’ and ‘Anesthetized’ states are statistically significant (ANOVA F-test, α = 0.05, p = 0).
Figure 3.
Individual GC values for LOC and ROC conditions with 95% significance level.
(a) GCLF↔LP for patient S11 at LOC. (b) GCRF↔LP for patient S1 at ROC. (c) GCLF↔RP for patient S13 at LOC. (d) GCRF↔RP for patient S17 at ROC. (e) GCRF↔LP for patient S8 at LOC. (f) GCLF↔RP for patient S21 at ROC. Vertical line indicates anesthetic administration ((a), (c), (e)), and recovery of consciousness ((b), (d), (f)). Outlier GC values due to the presence of artifacts in the raw EEG signal are also visible in (a) and (b).
Table 1.
Average classification performance for each subject at anesthesia induction (LOC).
Table 2.
Average classification performance for each subject at recovery of consciousness (ROC).
Figure 4.
Average classification performance (mean ± standard deviation) for LOC (top) and ROC (bottom) conditions.
Table 3.
Statistical significance of linear Vs non-linear classification.
Table 4.
Statistical significance of LOC Vs ROC classification.
Table 5.
Quantitative comparison with other methods reported in the literature.
Figure 5.
Granger Causality features for 50-Hz notch filtered and unfiltered data.
A: GC between left frontal and right posterior areas for patient S17; B: GC between right frontal and left posterior areas for patient S1. GC is shown for notch filtered EEG (top panels of A and B) and unfiltered EEG (bottom panels of A and B). Vertical lines denote anesthetic induction (dashed line) and recovery of consciousness (dotted line). The effects of diathermy artifacts on the GC estimates can also be identified as sharp outliers.