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. 2022 Sep 15;10(9):2295. doi: 10.3390/biomedicines10092295

Figure 5.

Figure 5

Posterior intracortical electrode—schematic representations of the atlas-based, histological, and MRI-guided coordinates in each rat of the EEG and MRI cohorts. (A) Anteroposterior (AP) coordinate. In the EEG cohort (n = 47, electrode operation right after injury), the fixed atlas-based target AP coordinate of −7.56 mm from the bregma was applied to implant the electrodes (orange dots). In the MRI cohort (n = 40, electrode operation at 5 months postinjury), the target AP coordinate was individually determined using the in vivo 5-month T2-weighted MR images. The target coordinate fluctuated depending on the TBI (traumatic brain injury)-induced lesion extent. Note a mild anterior shift (y-axis) in the histologically verified “true” AP coordinate (blue dots) relative to the target coordinate (orange dots) in both cohorts. In general, the anterior shift was less than that in a case of the anterior intra-cortical electrode (compare to Figure 1). Animal numbers are shown on the x-axis. (B) Mediolateral (ML) coordinate. In the EEG cohort (n = 47), the fixed atlas-based ML coordinate at 4 mm lateral to midline was targeted. In the MRI cohort (n = 40), the target ML coordinate was individually determined using the 5-month MRI. Note almost a negligible deviation of the histologically verified “true” ML coordinate from the atlas-based (EEG cohort) or MRI-guided (MRI cohort) coordinates. (C) Dorsoventral (DV) coordinate. In both cohorts, the lower tip of the bipolar electrode was targeted to layer V in the selected AP and ML coordinates (see above). In the EEG cohort, 46% (18/39), and in the MRI cohort, 66% (19/29) of the electrode tips in injured animals were in the cortex. Importantly, even though the lower tip in the remaining cases went down into the external capsule or corpus callosum, the upper tip of the bipolar electrode, being 1 mm higher in the EEG and 0.5 mm in the MRI cohort, was still recording in the cortex in 79% (31/39) of the rats in the EEG cohort and in 72% (21/29) in the MRI cohort. In 5 rats (3 sham, 2 TBI) in the EEG cohort and 10 rats (4 sham, 6 TBI) in the MRI cohort, the electrode was recording hippocampal rather than cortical activity, which affected the interpretation of the EEG data. The percentages of electrode locations in the sham-operated and TBI animals are shown on the right side of the panel. (D) Dot plots of the AP and ML shift in the histological AP and ML coordinate, and % of electrode in the targeted layer V (number of cases in brackets). Note posterior shift of some TBI cases from the target (Y = 0). The y-axis represents distance from target coordinate (Y = 0) or % of cases in targeted area. Note that in 4 animals in the EEG cohort and 2 in the MRI cohort, the DV location of the electrode tip could not be reliably determined in histological sections. Abbreviations: cavity, cortical lesion cavity; cc, corpus callosum; cg, cingulum; dcw, deep cerebral white matter; ec, external capsule; fmj, forceps major corpus callosum; HC, hippocampus; S, subiculum; V, ventricle.