Children with well controlled epilepsy possess different spatio-temporal patterns of causal network connectivity during a visual working memory task

Abstract

Using spectral Granger causality (GC) we identified distinct spatio-temporal causal connectivity (CC) patterns in groups of control and epileptic children during the execution of a one-back matching visual discrimination working memory task. Differences between control and epileptic groups were determined for both GO and NOGO conditions. The analysis was performed on a set of 19-channel EEG cortical activity signals. We show that for the GO task, the highest brain activity in terms of the density of the CC networks is observed in α band for the control group while for the epileptic group the CC network seems disrupted as reflected by the small number of connections. For the NOGO task, the denser CC network was observed in θ band for the control group while widespread differences between the control and the epileptic group were located bilaterally at the left temporal-midline and parietal areas. In order to test the discriminative power of our analysis, we performed a pattern analysis approach based on fuzzy classification techniques. The performance of the classification scheme was evaluated using permutation tests. The analysis demonstrated that, on average, 87.6 % of the subjects were correctly classified in control and epileptic. Thus, our findings may provide a helpful insight on the mechanisms pertaining to the cognitive response of children with well controlled epilepsy and could potentially serve as "functional" biomarkers for early diagnosis.

Keywords: Causal connectivity networks; Children; Classification; EEG; Early diagnosis; Epilepsy; Spectral Granger causality; Working memory.

Fig. 1

Sub-graphs of temporal evolution of the total degree of the CCN for all group types [ET (orange line), ENT (red line), CT (grey line) and CNT (blue line)] which correspond to five common frequency bands (δ, θ, α, β and γ). Five grey-bars separate the post-stimulus period to five time-intervals of 80 ms duration (1: [35, 115] ms, 2: [135, 215] ms, 3: [235, 315] ms, 4: [335, 415] ms, 5: [435, 515] ms). (Color figure online)

Fig. 2

δ band. Top temporal evolution of the total degree of the CCN whose connections represent statistically significant differences in the GC distributions for each pair of electrodes for the 4 group comparisons: CT versus CNT (grey line), ET versus ENT (blue line), CT versus ENT (black line) and CNT versus ENT (red line). The post-stimulus period is divided into five characteristic time intervals of 80 ms duration (1: [35, 115] ms, 2: [135, 215] ms, 3: [235, 315] ms, 4: [335, 415] ms, 5: [435, 515] ms) are marked with grey bars. Bottom topographic maps of node degrees which correspond to 1, 2, 3, 4 and 5 time intervals marked with grey bars. (Color figure online)

Fig. 3

θ band. Top temporal evolution of the total degree of the CC networks whose connections represent statistically significant differences for the 4 group comparisons: CT versus CNT (grey line), ET versus ENT (blue line), CT versus ENT (black line) and CNT versus ENT (red line). The post-stimulus period is divided into five characteristic time intervals of 80 ms duration (1: [35, 115] ms, 2: [135, 215] ms, 3: [235, 315] ms, 4: [335, 415] ms, 5: [435, 515] ms) are marked with grey bars. Bottom topographic maps of node degrees which correspond to 1, 2, 3, 4 and 5 time intervals marked with grey bars. (Color figure online)

Fig. 4

α band. Top temporal evolution of the total degree of the CC networks of the CCN whose connections represent statistically significant differences for the 4 group comparisons: CT versus CNT (grey line), ET versus ENT (blue line), CT versus ENT (black line) and CNT versus ENT (red line). The post-stimulus period is divided into five characteristic time intervals of 80 ms duration (1: [35, 115] ms, 2: [135, 215] ms, 3: [235, 315] ms, 4: [335, 415] ms, 5: [435, 515] ms) are marked with grey bars. Bottom topographic maps of node degrees which correspond to 1, 2, 3, 4 and 5 time intervals marked with grey bars. (Color figure online)

Fig. 5

β band. Top temporal evolution of the Total-Degree of the CC networks of the CCN whose connections represent statistically significant differences for the 4 group comparisons: CT versus CNT (grey line), ET versus ENT (blue line), CT versus ENT (black line) and CNT versus ENT (red line). The post-stimulus period is divided into five characteristic time intervals of 80 ms duration (1: [35, 115] ms, 2: [135, 215] ms, 3: [235, 315] ms, 4: [335, 415] ms, 5: [435, 515] ms) are marked with grey bars. Bottom topographic maps of node degrees which correspond to 1, 2, 3, 4 and 5 time intervals marked with grey bars. (Color figure online)