Exploring high-frequency oscillation as a marker of brain ischemia using S-transform

Area of Science:

• Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Brain injury, particularly hypoxic-ischemia following cardiac arrest, significantly alters somatosensory evoked potential (SSEP) signals.
• These alterations in SSEP hold diagnostic potential for assessing brain injury severity and recovery.
• High-frequency oscillations (HFOs) within SSEP signals are complex and require advanced analysis techniques for characterization.

Purpose of the Study:

• To investigate the characteristics and evolution of high-frequency oscillations (HFOs) within SSEP signals during early recovery from brain injury in a rat model.
• To compare different time-frequency analysis methods for optimal characterization of HFOs.
• To determine if HFOs can serve as a biomarker for brain injury outcome and reflect the health of thalamocortical circuitry.

Main Methods:

• Development and comparison of time-frequency representation strategies, including the S-transform (ST) and phase ST (inter-trial coherence, ITC).
• Application of ST and ITC to analyze HFOs in SSEP signals recorded from a rat model of asphyxial cardiac arrest.
• Statistical analysis to compare HFO amplitude and recovery dynamics between good- and bad-outcome groups.

Main Results:

• The S-transform (ST) effectively localized HFOs in temporal-spectral space, while phase ST (ITC) sensitively detected phase-locked activities.
• A notable discrepancy was observed: HFO amplitude increased over time during recovery, while HFO phase remained time-invariant.
• HFO amplitude recovery dynamics paralleled that of the N10 component, suggesting HFOs precede larger cortical responses.
• Significant differences in HFO amplitude levels (p < 0.05) and recovery dynamics (p = 0.03) were found between good- and bad-outcome groups.

Conclusions:

• HFOs in SSEP signals are valuable for characterizing brain injury and recovery after cardiac arrest.
• The distinct recovery patterns of HFO amplitude and phase provide insights into neural recovery mechanisms.
• HFOs show promise as a biomarker for predicting neurological outcome and reflecting the integrity of thalamocortical circuitry in ischemic brain injury.