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Quantifying cortical EEG responses to TMS in (un)consciousness
Simone Sarasso1, Mario Rosanova, Adenauer G Casali
1Department of Biomedical and Clinical Sciences "Luigi Sacco," University of Milan, Milan, Italy.
Clinical EEG and Neuroscience
|January 10, 2014
Summary
Measuring brain complexity using Transcranial Magnetic Stimulation (TMS) combined with electroencephalography (EEG) offers an objective assessment of consciousness. This method reliably detects changes in brain complexity during sleep, anesthesia, and brain injury, aiding in diagnosing consciousness disorders.
Area of Science:
- Neuroscience
- Cognitive Science
- Neurology
Background:
- Assessing consciousness typically relies on external interactions and communication, which are insufficient for detecting consciousness independent of external stimuli.
- A reliable, objective measure of consciousness, independent of sensory processing and motor output, is currently lacking.
- Consciousness is theoretically linked to brain complexity, specifically the integration and differentiation of neural activity.
Purpose of the Study:
- To review studies using Transcranial Magnetic Stimulation combined with electroencephalography (TMS/EEG) to quantify brain complexity.
- To explore the utility of TMS/EEG in assessing consciousness across various states (wakefulness, sleep, anesthesia, brain injury).
- To discuss the potential of this approach in understanding the pathophysiology of disorders of consciousness.
Main Methods:
- Utilizing Transcranial Magnetic Stimulation (TMS) to stimulate the brain and electroencephalography (EEG) to record the cortical response.
- Quantifying brain complexity by analyzing the TMS-evoked EEG signals.
- Comparing brain complexity measurements across different states of consciousness, including wakefulness, sleep, anesthesia, and disorders of consciousness.
Main Results:
- Brain complexity, as measured by TMS/EEG, significantly decreases during loss of consciousness (deep sleep, anesthesia, vegetative state).
- Cortical response complexity recovers with the resurgence of consciousness (wakefulness, dreaming, minimally conscious state, locked-in syndrome).
- TMS/EEG provides a quantifiable measure of brain complexity that correlates with the level of consciousness.
Conclusions:
- TMS/EEG offers a promising objective method for measuring brain complexity and assessing consciousness.
- This approach can aid in diagnosing and understanding disorders of consciousness in brain-injured patients.
- Further methodological refinement of TMS/EEG for brain complexity measurement is crucial.
