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Abstract

Objective
Mismatch negativity (MMN) is an automatic event-related brain response, well studied in the acute phase after severe brain injury: the presence of an MMN has often been shown to predict awakening from coma and the exclusion of switching to a vegetative state (VS). In the current study, MMN was examined during the recovery of VS.

Methods 
Ten vegetative patients were examined repeatedly every 2 weeks for an average period of 3.5 months. Amplitudes and latencies were related to the recovery of the patients from VS to consciousness, and with a healthy norm group. In addition, MMN was investigated for its prognostic value in VS patients, in predicting recovery to consciousness and long-term functional outcome.

Results 
Upon recovery to consciousness, MMN amplitudes increased. A sudden increase in MMN amplitude was observed when patients began to exhibit inconsistent behavioral responses to simple commands. At this level, MMN resembled the MMN response as seen in the norm group. In addition, the MMN amplitude and latency during the initial measurement predicted the patient's outcome in recovery to consciousness.

Conclusions
With recovery from VS to consciousness, the ability to process auditory stimulus deviation increases. A sudden amplification of the MMN amplitude preceded overt communication with the environment. This may be indicative of the consolidation of neural networks that underpin overt communication. Additionally, MMN can be helpful in identifying the ability to recover from VS.

Meaning
MMN can be used to monitor recovery from the vegetative state in the postacute phase after severe brain injury. In addition, MMN can be used to predict the ability to recover from the vegetative state.

Keywords
Mismatch negativity, Vegetative state, Minimally conscious state, Consciousness