The detection of psychophysiological parameters in vegetative state patients: a response to sensory stimulation?

This study aims to find psychophysiological markers of state of consciousness in response to sensorial stimuli addressed to vegetative state patients. A set of stimuli is presented to a sample of 18 vegetative state patients; stimuli belong to four cathegories, different for sensorial channel used: visive, uditive, tactile, olfactory. For visive and uditive stimuli there is a distinction between autobiographical and not-autobiographical stimuli, id est patients’ photos and name versus others’ photos and names. Instead tactile stimuli are a close to the wrist and the application of ice on the wrist, while olfactory stimuli are vanilla and cinnamon fragrances. Visive and uditive stimuli are presented by a eventrelated paradigm, while tactile and olfactory stimuli are presented as single trial. During the entire stimuli presentation, cortical activity and physiological activation are recorded by electroencephalography and biofeedback. Data showed a significative ERP P300 component in response to autobiographical visive and uditive stimuli. Subjects seem to be able to recognise an autobiographical stiumulus between various non autobiographical stimuli. P300 ERP occurs only during attentional envolvement in a cognitive task and seems to be linked to attentive and conscious processes. We could infer the presence of preserved cognitive abilities, even without significant behavioral responses. It can be assumed that asscociative cortex in vegetative state patients is partially active and involved with sensory cortex, since P300 ERP (as well as all potential registered more than 100 ms after stimulus presentation) typically reflects the activation of the associative cortex. However, the thalamus-cortical and cortico-cortical disconnection remains massive in this type of patients, in fact there is no ability to perform voluntary actions and there is an absolute predominance of the delta band for cortical activity, typical of neurological diseases and cortico-cortical and thalamic-cortical disconnections. Moreover, any evidence of awareness is shown by behavioral data and autonomic responses.