Psychophysiological measures for vegetative state assessment

Objective: The present research’s aim was to find state of consciousness psychophysiological markers in response to sensorial stimuli where behavioural evidences of awareness are not clear: vegetative state patients. Participants and Methods: A sample of 23 vegetative state patients was assessed with a set of multi-sensory stimuli. Tactile stimuli were a wrist hold and ice application; olfactory stimuli were vanilla and cinnamon fragrances. During the whole stimuli presentation, cortical activity (EEG) and physiological activation (biofeedback) were recorded. Results: Results showed a physiological arousal increasing with greater skin conductance levels and heart rate in response to vanilla and ice compared, respectively, to cinnamon and wrist hold stimuli. Data from cortical activity confirmed physiological activation, with a higher Theta band activity in left frontal cortex for vanilla fragrance and at right for cinnamon fragrance. This lateralization seemed to highlight stimuli pleasantness (higher left frontal activation for vanilla) and stimuli unpleasantness (higher right frontal activation for cinnamon). The different physiological activation should be probably due to pleasantness for vanilla stimulus. Patients’ responses to ice application, instead, were maybe due to a state of alert. More compromised patients, in fact, seemed to detect ice as a potentially dangerous stimulus for their organism and not only as a distress stimulus. Conclusions: In conclusion, even if explicit stimuli processing and interpretation were probably impeded by cortico-talamic disconnections, covert responses, as shown by both EEG and autonomic results, could be used to bypass this obstacle.