We read with interest the article by Chennu et al (2014) on spectral signatures in persons with disorders of consciousness and believe a few additional comments are worthwhile noting. There have been many recent advances in disorders of consciousness and more focus on the specific behavioral state of the patient regardless of how they may present clinically at the bedside (Gosseries, Zasler, Laureys, 2014). The term ‘functional locked-in syndrome’ has been proposed to describe patients with a dissociation between extreme motor dysfunction and preserved higher cortical functions identified only by functional imaging techniques (Bruno et al., 2011). Moreover, Cruse at al. (2011) demonstrated that it is also possible to detect the hidden awareness of patients in behavioural vegetative state, using an electroencephalographic (EEG) technique. Nevertheless, patients clinically diagnosed in the vegetative state who are able to perform mental imagery tasks (Owen et al., 2006; Monti et al., 2010) are still considered to be in the vegetative state with preserved islands of consciousness, not as having functional locked-in syndrome (Formisano et al., 2011a,b; 2013). Indeed, patients with residual cognitive functions, who are able to perform complex mental imagery tasks or show intentional communication ability with functional neuroimaging techniques, should be diagnosed with functional locked-in syndrome and not vegetative state with hidden consciousness (Formisano et al., 2013). Interestingly, Chennu et al., (2014) applied graph theory by means of high-density electroencephalographic investigation of a series of patients with chronic disorders of consciousness. The metric of alpha network efficiency also correlated with the degree of behavioral awareness. In particular, some patients in behaviorally unresponsive vegetative states who demonstrated evidence of covert awareness with functional neuroimaging, had alpha networks that were preserved and similar to those of the controls. These findings parallel the alpha rhythm commonly found in patients with locked-in syndrome and supports our hypothesis that behaviorally unresponsive patients who follow commands based on functional neuroimaging or neurophysiological tests are not, in fact, in a vegetative/unresponsive wakefulness syndrome (von Wild et al., 2011), but instead in a complete locked-in or functional locked-in syndrome.

Dr. Rita Formisano


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