Between life and death: the brain twilight zones

Area of Science:

• Neuroscience
• Physiology
• Medical Law

Background:

• Clinical death is legally defined by irreversible cessation of brain activity.
• Cardiorespiratory failure causes complex, time-dependent neuronal changes reversible by resuscitation.
• Current event-based models of death are neurophysiologically inadequate.

Purpose of the Study:

• To review brain activity changes during dying and resuscitation.
• To propose a new mixed (event-process) model of death and resuscitation.
• To integrate dying brain phases into a continuum of declining brain activity.

Main Methods:

• Review of experimental and clinical evidence on brain activity during dying and resuscitation.
• Analysis of anoxia-dependent brain defects and their sequence.
• Identification of biomarkers like the 'wave of death' and 'wave of resuscitation'.

Main Results:

• Dying involves sequential brain changes: EEG alterations, isoelectric state, loss of consciousness, increased resistivity, 'wave of death' (terminal spreading depolarization), and terminal isoelectric state.
• Resuscitation can initiate a mirrored sequence: neuronal repolarization and re-emergence of electrical activity.
• A 'wave of resuscitation' marks neuronal electrical property recovery during reoxygenation.

Conclusions:

• The dying process is a continuum of declining brain activity, not an abrupt event.
• The proposed mixed model incorporates 'cerebral twilight zones' and characteristic cortical waves.
• Real-time biomarkers of death and resuscitation can be identified.