# Cortical Connectivity Response to Hyperventilation in Focal Epilepsy: A Stereo-EEG Study
## 4 Results  
The study included a total of 10 patients (6 Males), with a mean age of 37 years at the time of SEEG implantation. As shown in Table 1, it was possible to delineate an EZ that was located in the temporal lobe in seven patients, temporal-occipital cortex in two patients, and frontal in one patient. All the SEEG implants were unilateral (7 right, 3 left) and included 15 electrodes on average. In particular, four patients underwent temporo-parieto-occipital exploration, three fronto-temporal, two fronto-temporo-parietal, and one temporal. At the time of the study, six patients underwent epilepsy surgery, and the histopathological analysis revealed hippocampal sclerosis in four cases, focal cortical dysplasia in one case, and aspecific findings in the remaining one. Our analysis focused on the following metrics: the energy ratio (\(ER\)), the entropy (\(H(\theta)\)) of the spectral phase distribution, and the Phase Transfer Entropy (\(PTE\)) computed from the instantaneous phase distribution. As shown in Table 2, both the ictal and awake periods presented higher energy ratio values than N-REM and awake periods. The energy ratio proved to be an effective biomarker for discerning HV activities from the N-REM conditions since it was sensibly lower when patients performed the HV maneuver. Taking the interquartile range into account, the differences are the same as those expressed in terms of median: in other words, the epochs presenting higher energy values are also associated with higher energy variability. Notably, there was slight evidence (\(p\)-value 0.09) that ictal transitions present more variable energy ratios than awake periods, although the latter showed higher median values for this metric (0.0672 vs. 0.0600). The entropy measures allowed us to differentiate between the ictal and the awake epochs from the N-REM and HV epochs (Table 3). At the same time, no significant difference was observed when comparing the ictal transition with the awake status, as well as the HV maneuver with the N-REM phase. Taking the interquartile range into account, the results followed an opposite trend compared to that before since higher entropy values were associated with lower entropy variability. The entropy during the ictal transition was slightly more variable (\(p\)-value of 0.063) than the one measured during the awake periods. In general, the variability was maximized during the ictal transition (with a value of 0.0988) and minimized during the HV (with a value of 0.0383). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & **Patient 1** & **Patient 2** & **Patient 3** & **Patient 4** & **Patient 5** & **Patient 6** & **Patient 7** & **Patient 8** & **Patient 9** & **Patient 10** \\ \hline Age (SEG) & 24 & 39 & 50 & 39 & 36 & 52 & 36 & 24 & 25 & 48 \\ \hline Sex & Male & Male & Female & Female & Male & Female & Male & Female & Male \\ \hline EZ localization & Left F & Left T & Left T & Right T-O & Right T & Left T & Right T & Right T & Right T \\ \hline SEEG implant & Left F-T & Left F-T-P & Left F-T-P & Right T-P & Right F-T & Left T & Right T-P-O & Right F-T \\ \hline Surgery & THC & THC + Left ATL & THC & THC & THC + Right ATL & THC & THC + Left & THC & THC + Right ATL & Right ATL \\ \hline Histopathology & N/A & HS 1 & HS 1 & N/A & N/A & HS 1 & FCD & N/A & ApSpecific & HS 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Clinical and demographic characteristics of the studied population; F is for Frontal, T for Temporal, O for Occipital, THC for Thermocogaulation, ATL for Anterior Temporal Lobectomy, HS for Hippocamp Sclerosis, and FCD for Focal Cortical Dysplasia.