Diagnostic accuracy of intraoperative neuromonitoring in transcarotid artery revascularization.

BACKGROUND: In recent years, transcarotid artery revascularization (TCAR) has emerged as a safe and effective alternative to carotid artery stenting. While intraoperative neuromonitoring (IONM) techniques such as electroencephalogram (EEG) and somatosensory evoked potentials (SSEPs) are often employed during TCAR, there is limited research on their diagnostic accuracy. METHODS: The authors retrospectively reviewed a multi-institutional IONM database of TCAR procedures performed with EEG and SSEP monitoring. A total of 516 TCAR procedures were included in this study. Significant changes in EEG and/or SSEPs, surgeon's interventions, resolution of significant changes, and immediate postoperative neurological outcome were documented. Sensitivity, specificity, positive and negative predictive values were calculated. RESULTS: The incidence of intraoperative onset new neurologic deficit was 0.4%. Significant changes in EEG and/or SSEPs occurred in 5.4% of the cases. Of the cases with IONM alerts, 78.5% returned to baseline with a surgical or hemodynamic intervention. From the cases with unresolved IONM alerts, 33.3% woke up with a new neurological deficit. The overall sensitivity and specificity for IONM was 100% and 99.2%, respectively. The positive predictive value was 33.3% and the negative predictive value was 100%. CONCLUSIONS: IONM during TCAR offers high sensitivity and specificity in predicting postoperative outcome. Patients with resolved IONM alerts had immediate neurological outcomes that were comparable to those who had no IONM alerts.

Synchronous oscillatory neural ensembles for rules in the prefrontal cortex.

Intelligent behavior requires acquiring and following rules. Rules define how our behavior should fit different situations. To understand its neural mechanisms, we simultaneously recorded from multiple electrodes in dorsolateral prefrontal cortex (PFC) while monkeys switched between two rules (respond to color versus orientation). We found evidence that oscillatory synchronization of local field potentials (LFPs) formed neural ensembles representing the rules: there were rule-specific increases in synchrony at "beta" (19-40 Hz) frequencies between electrodes. In addition, individual PFC neurons synchronized to the LFP ensemble corresponding to the current rule (color versus orientation). Furthermore, the ensemble encoding the behaviorally dominant orientation rule showed increased "alpha" (6-16 Hz) synchrony when preparing to apply the alternative (weaker) color rule. This suggests that beta-frequency synchrony selects the relevant rule ensemble, while alpha-frequency synchrony deselects a stronger, but currently irrelevant, ensemble. Synchrony may act to dynamically shape task-relevant neural ensembles out of larger, overlapping circuits.