Psychophysiological indices in vegetative state patients: a conscious response to sensorial stimuli?

Objective This study aims to find state of consciousness psychophysiological markers response to sensorial stimuli addressed to vegetative state patients in order to get covert responses under a lack of behavioural evidences of stimuli awareness. Participants and methods A set of sensorial stimuli is presented to a sample of 18 vegetative state patients. Auditory stimuli were in patients’ name (target stimulus) versus others names. Tactile stimuli were a close to the wrist and the application of ice; olfactory stimuli were vanilla and cinnamon fragrances. During stimuli presentation, cortical activity and physiological activation were recorded by electroencephalography and biofeedback. Results Data show an increasing of skin conductance of level (SCL) and heartbeat for auditory target stimulus compared to other names hearing, for vanilla and ice. Furthermore, a low level of SCL was observed in patients with a less compromised state of consciousness. A greater Theta band activity (4-7.5 Hz) was present in left frontal cortex for vanilla and at right for cinnamon. A greater Beta band (13-30Hz) in temporal area was present while earing uditive target stimuli. Conclusion Differences in physiological activation should be probably due to the exposure to familiar stimuli for the auditory one and due to pleasantness for the vanilla flavour. Responses to ice, instead, maybe due to a state of alert; in fact it’s possible that more compromised patients relieve ice as dangerous for the organism and not only as a distressing stimulus. The lateralization of Theta band activation for olfactory stimuli could reflect the pleasentness (left) and unpleasentness (right) of them. Greater Beta band in temporal area suggests a different elaboration between uditive target and non-target stimuli, even if it can’t be interpreted consciously. Stimuli interpretation is obstacled by cortico-talamic disconnections, but sensorial deprivation can be avoided considering covert responses and not only behavioural one.