Abstract
The ability to recognize one’s own face, or “self-face”, is a hallmark of self-awareness. In healthy subjects, the sympathetic skin response (SSR) evoked by self-face recognition has a greater area than responses evoked by other visual stimuli. We evaluated the SSRs evoked by self-face images and by six other visual stimuli (conditions) in 15 patients with severe disorders of consciousness and in 15 age-matched healthy subjects. Under all conditions, the evoked area of the SSR was smaller in patients with unresponsive wakefulness syndrome (UWS), intermediate in patients in a minimally conscious state (MCS), and greater in healthy subjects. In patients with UWS, no differences were found between the SSR area evoked by self-face images and those evoked by other conditions. In patients in an MCS, the area of the SSR evoked by self-face presentation was greater than those evoked by other conditions, but statistical significance was reached only in the comparison to other stimuli not involving a real face. This finding may be due to the inability of these patients to differentiate their own face from those of others. These results probably reflect a varying level of self-awareness and suggest some diagnostic implications in patients with severe disorders of consciousness.
Highlights
Distinguishing patients with a very low level of consciousness from patients who are fully unconscious can be a difficult task
The sympathetic skin response (SSR) area evoked by one’s own face was greater than those evoked by all other conditions in 14 of the 15 healthy subjects
Post hoc analysis demonstrated that the SSR area evoked by the self-face was significantly greater than that evoked by the other conditions (“face” vs. “board,” “snake,” “stylized face,” “scream,” “unknown,” or “well-known,” P < 0.001)
Summary
Distinguishing patients with a very low level of consciousness (i.e. who are in a minimally conscious state [MCS]) from patients who are fully unconscious (i.e. who have unresponsive wakefulness syndrome [UWS]) can be a difficult task. UWS (previously known as vegetative state) and MCS can result from severe brain injuries that deeply affect the ability of the brain to generate consciousness. Patients with UWS are able to open their eyes spontaneously, but they lack any sign of self- or environmental awareness (Royal College of Physicians, 2003). Differential diagnosis between UWS and MCS raises serious problems, because the current diagnostic criteria are still based on a careful (but subjective) clinical assessment of the patient’s spontaneous and elicited behaviors (Giacino et al, 2002; Royal College of Physicians, 2003). Diagnostic errors arise from the difficulty of assessing low levels of responsiveness because
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