Fronto-parietal network in response to pleasant and unpleasant somatic stimuli in DoC patients: a pilot study

The assessment of responsivity and preserved cognitive functioning in patients presenting a vegetative state (VS) is primarily based on the observation of overt response patterns, which is however often difficult to classify. This pilot study investigates the potential of EEG oscillations as covert measures to detect residual processing of pleasant/unpleasant somatic stimuli in VS patients. 22 VS patients received two somatic stimulations – a wrist grasp and the placement of an ice pack on their wrist – during EEG recording. Results showed that both pleasant and unpleasant stimulations elicited increased frontal and parietal delta power, with greater parietal responses during the unpleasant stimulations than the pleasant ones. Pleasant stimulations were associated to greater decrease of alpha activity in left frontal areas compared to the unpleasant ones. These activation patterns might mirror basic vigilance responses to external stimuli, supported by residual fronto-parietal interactions. Analysis of EEG profiles during somatic stimulations might point out informative patterns of oscillatory responses.