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Preserved feedforward but impaired top-down processes in the vegetative state
Melanie Boly1, Marta Isabel Garrido, Olivia Gosseries
1Coma Science Group, Cyclotron Research Centre and Neurology Department, University of Liège and CHU Sart Tilman Hospital, 4000 Liège, Belgium. mboly@ulg.ac.be
Science (New York, N.Y.)
|May 14, 2011
Summary
Impaired top-down processing in the brain, specifically backward connectivity from frontal to temporal cortices, is a key indicator of consciousness in severely brain-damaged patients. This finding highlights the role of recurrent processing in conscious perception.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Clinical Neurology
Background:
- Frontoparietal cortex plays a role in both explicit and subliminal stimulus processing.
- Consciousness in severely brain-damaged patients is difficult to assess reliably.
- Top-down processes and long-latency electrophysiological responses are potential correlates of consciousness.
Purpose of the Study:
- To investigate the role of top-down processing in consciousness.
- To identify reliable neural correlates of consciousness in vegetative state patients.
- To compare frontoparietal responses with recurrent processing measures.
Main Methods:
- Measured effective connectivity using a mismatch negativity paradigm.
- Compared brain activity between patients in a vegetative state and healthy controls.
- Focused on backward connectivity from frontal to temporal cortices.
Main Results:
- The primary difference observed was impaired backward connectivity in vegetative state patients compared to controls.
- Frontoparietal responses did not show significant differences.
- This impairment in top-down projections was specific to recurrent processing.
Conclusions:
- Impaired backward connectivity from frontal to temporal cortices is a reliable correlate of consciousness in severely brain-damaged patients.
- Top-down projections are crucial for recurrent processing and conscious perception.
- This finding emphasizes the importance of assessing recurrent neuronal message-passing for consciousness evaluation.
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