Pain in prolonged disorders of consciousness: laser evoked potentials findings in patients with vegetative and minimally conscious states

INTRODUCTION: Pain perception is currently an open question in patients suffering from prolonged disorders of consciousness. The aim of the present study was to examine nociceptive specific laser evoked responses (LEPs) in view of long-latency evoked potentials by non-painful electrical stimuli (SEPs) and auditory mismatch negativity (MM). METHODS: Three vegetative state (VS), four minimal Conscious State (MCS) patients and 11 age- and sex-matched controls were examined. Evoked responses were obtained by 64 scalp electrodes, stimulating the dorsum of the right hand by noxious laser and innocuous electrical stimulus, according to normal controls subjective rating. An auditory paradigm for MM was also employed. RESULTS: The MM was present in all patients. The LEP vertex complex was recognizable in all cases, with a significant latency increase of both N2 and P2 which displayed changes of topographic representation. Late SEPs were absent in all patients except in one MCS case, who showed a significant N2 and P2 latency increase. DISCUSSION: The results may suggest that high relevant stimuli may be processed even in patients with severe brain damage. Larger series and multimodal approaches may contribute to confirm that cortical arousal toward pain salience may be a primary function for life persistence