ABSTRACT
OBJECTIVE: Patients with the unresponsive wakefulness syndrome (UWS; formerly vegetative state) or in a minimally conscious state (MCS) open their eyes spontaneously but show no (UWS) or only marginal (MCS) signs of awareness. Because these states can become permanent, residual information processing capacities need to be determined, and reliable outcome predictors need to be found. We assessed higher-order cortical information processing in UWS or MCS in a large group of patients using electroencephalographic event-related potentials (ERPs) and determined their long-term prognostic value for recovery. METHODS: Cognitive ERPs elicited by sound (P300) and speech (N400) were used to assess information processing in 92 behaviorally unresponsive patients diagnosed as in the state of either UWS (n=53) or MCS (n=39). ERPs were assessed with a clinical standard evaluation method and a computerized method, the t-continuous wavelet transform. The patients' clinical outcome was followed up between 2 and 14 years after discharge from the rehabilitation center. RESULTS: Within the first year of the disease, many patients showed an intact P300 and several also an N400, indicating considerable residual information processing. At clinical follow-up, about 25% of the patients recovered and regained communicative capabilities. A highly significant relationship between N400, but not P300, presence and subsequent recovery was found. INTERPRETATION: Results specify cognitive capabilities in disorders of consciousness, and determine their prognostic value. Specifically the N400 ERP is suggested as an important tool to assess information-processing capacities that can predict the likelihood of recovery of patients in UWS or MCS.
Subject(s)
Cognition Disorders/etiology , Consciousness Disorders/complications , Evoked Potentials/physiology , Recovery of Function/physiology , Speech Disorders/etiology , Adult , Aged , Cognition Disorders/diagnosis , Electroencephalography , Female , Follow-Up Studies , Humans , Male , Middle Aged , Predictive Value of Tests , Severity of Illness Index , Spectrum Analysis , Speech Disorders/diagnosisABSTRACT
When people detect their own errors in a discrimination task, a negative-going waveform can be observed in scalp-recorded EEG that has been coined the error-related negativity (Ne/ERN). Generation of the Ne/ERN has been associated with structures in the prefrontal cortex, especially the anterior cingulate region, but also the supplementary motor cortex and subcortical structures. There is some controversy as to whether the Ne/ERN is a necessary concomitant to error detection. We examined the Ne/ERN in five patients with damage to the medial prefrontal cortex, including the anterior cingulate region. Our findings support the implication of the rostral anterior cingulate in Ne/ERN production, but they also show that subjects can be aware of errors and yet not produce an Ne/ERN. Thus, error detection leads to the Ne/ERN process and damage to the anterior cingulate region may interrupt this relay, suggesting that error detection may be supported by circuits outside the anterior cingulate region.
