Table 1.
Patient Collective: m = male, f = female, Age (at the time of operation), Duration since diagnosis (number of years since disease diagnosis).
Score of the motor part of the Unified Parkinson’s Disease Rating Scale (UPDRS) without medication: UPDRS Off, score of the motor part of the UPDRS with medication: UPDRS On. The UPDRS test was performed prior to surgery.
Fig 1.
Example of long-latency somatosensory evoked potential (LL-SSEP) Complex, Patient 4, right STN, monopolar reference, contralateral median nerve stimulation (MNS).
Black: Contact 0, red: Contact 1, blue: Contact 2, green: Contact 3.
Fig 2.
Zoom-in view of Fig 1 emphasizing the short-latency somatosensory evoked potential (SL-SSEP) component N20: Patient 4, right STN, monopolar reference, contralateral median nerve stimulation (MNS).
Black: Contact 0, red: Contact 1, blue: Contact 2, green: Contact 3.
Table 2.
Statistical comparison of mean latencies between the N18/20 in the present study and data reported in the literature revealed no significant difference (significance level of 0.05).
N denotes the number of nuclei with occurrence of the N18/20, Latency (ms): Mean ± standard deviation (SD) (range), Amplitude (μV): Mean ± SD (range), NA “not available”. This finding provides support for the used methodology, namely forehead rather than linked earlobes/mastoids for monopolar reference and filtering methods (Notch and 40 Hz high cut-off), in eliciting somatosensory evoked potentials (SSEPs).
Table 3.
Long-latency somatosensory evoked potential (LL-SSEP) components corresponding to monopolar data: N denotes the number of nuclei with a referred wave, Latency (ms): Mean ± SD (range), Amplitude (μV): Mean ± SD (range).
Fig 3.
Example of LL-SSEPs recorded with bipolar reference.
Left: Phase reversal of the P140 and the N200, Patient 2, left STN, ipsilateral MNS. Right: Maximum amplitude of the P80 and N140, contact (1 vs. 2), Patient 4, right STN, contralateral MNS.
Table 4.
LL-SSEP components corresponding to bipolar data: N denotes the number of nuclei with a referred wave, Latency (ms): Mean ± SD (range), Amplitude (μV): Mean ± SD (range), “Total Phase reversals” denotes the total number of reversals across bipolar contacts for each LL-SSEP component and stimulation side, “Max 1–2” denotes the number of nuclei with maximum amplitude at bipolar contact (1 vs. 2).
Fig 4.
Example of LL-SSEPs recorded with bipolar reference.
Left: Phase reversal of the P80 at contact (0 vs. 1), Patient 9, right STN, ipsilateral MNS. Right: Phase reversal of the N100 at contact (2 vs. 3), Patient 2, left STN, contralateral MNS.
Table 5.
Number of phase reversals for each bipolar contact, LL-SSEP component and stimulation side (ipsi- and contralateral).
No significant difference was found in the number of phase reversals between bipolar contacts according to the Wilcoxon signed-rank test (p = 0.157 for ((0 vs. 1) vs. (1 vs. 2)), p = 0.395 for ((1 vs. 2) vs. (2 vs. 3)), p = 1.0 for ((0 vs. 1) vs. (2 vs. 3))).