Sensorial stimulation in vegetative state patients: what kind of response?

Background Responsivity assessment and preserved cognitive abilities detection in vegetative state (VS) patients is usually observationdriven and based on overt responses that are often difficult to classify. The same is true for inferring subjective experiences like somatosensory percept and pain. Thus, electrophysiological covert measures could be considered a helpful tool to provide remarkable information on patients’ responsivity to environmental stimuli. Residual processing of somatosensory and nociceptive stimuli in VS patients in absence of behavioural evidences were investigated by observing cortical oscillations and physiological activation. Materials and Methods A sample of 22 VS patients received a wrist hold and the application of an ice pack to induce somatosensory activations related to, respectively, pleasant and unpleasant stimulations. Cortical activity (measured by EEG) and physiological activation measures were acquired during the sensorial stimulation. Results Autonomic indices showed greater skin conductance levels and greater heart rate in response to ice compared to the wrist hold. EEG measures highlighted higher frontal and parietal delta band power evoked by both pleasant and unpleasant stimulations. Specifically, unpleasant stimulation aroused greater delta parietal responses than the pleasant ones, while pleasant stimulations were associated to greater decrease of alpha activity in left frontal areas. Conclusions These patterns of neurophysiological activity might be interpreted as preserved basic vigilance responses to environmental stimuli in this cohort of patients. The analysis of EEG profiles during somatic stimulations might suggest informative patterns of different oscillatory responses (different modulations of alpha and delta activity), giving insights on the opportunity to test basic responsivity in patients with disorders of consciousness.