Passive mapping of hand motor cortex across altered states of consciousness.

Median nerve stimulation combined with high gamma band activity can map the hand motor cortex during awake states, but its effectiveness declines with loss of consciousness. In five patients undergoing awake craniotomy, the sensitivity of mapping using the short-latency average envelope remained relatively stable, dropping only from 100% awake to about 82% during deeper anesthesia stages. In contrast, mapping based on average power deteriorated more sharply, from 100% awake to around 21% at the deepest stage. The long-latency average envelope also showed reduced sensitivity as consciousness declined, with a slope coefficient significantly smaller than that for short-latency responses. These results suggest that short-latency envelope-based mapping is more robust across different conscious states.

Study at a glance

Abstract

To evaluate the ability of median nerve stimulation (MNS)-induced high gamma band (HGB) activity in mapping the hand motor cortex at different states of consciousness. Five patients undergoing awake craniotomy were recruited. MNS-induced electrocorticographic signals were recorded from awake to anesthetic states, with the loss of consciousness (LOC) session divided into three stages (LOC1, LOC2, and LOC3) based on conscious level. HGB signals were analyzed to localize hand motor cortex. Linear models were applied to analyze HGB dynamics during LOC. The sensitivity of hand motor cortex mapping based on HGB average envelope at short-latency period was 100%, 96.67%±3.33%, 83.47%±8.19%, and 82.22%±11.44% for the awake, LOC1, LOC2 and LOC3 stages. The sensitivity for HGB average envelope at long-latency period was 92.67%±4.52%, 90.85%±4.13%, 72.27%±17.07%, and 40.53%±12.82% across the same stages. The sensitivity based on HGB average power at short-latency period decreased from 100% in awake stage to 72.83%±12.95%, 48.11%±15.95%, and 21.12%±5.70% across LOC stages. The sensitivity for HGB average power at long-latency period dropped from 92.67%±4.52% in awake stage to 70.94%±10.79%, 58.37%±17.49%, and 25.71%±14.95% in the subsequent LOC stages. The slope coefficient of the simple linear model for long-latency average envelope was significantly smaller than that for short-latency. In the linear mixed effects model, the Condition × Sliding Window estimate coefficient was -0.794. In awake state, HGB average envelope and average power both effectively localized hand motor cortex. With declining consciousness, the mapping ability of average power significantly deteriorated, while the mapping ability of short-latency average envelope remained relatively stable.