Temporal fluctuations of cognitively-mediated behaviors in minimally conscious state (MCS) have been linked to changes of awareness, but the time-pattern of these variations remains ill-described. We analyzed 4-h EEG recordings from 12 patients with disorders of consciousness (6 MCS and 6 vegetative state/unresponsive wakefulness syndrome, VS/UWS). Relative powers (delta, theta, alpha, beta1 and beta2 bands) and spectral entropy were estimated (Fz, Cz and Pz derivations). Spectral entropy time-courses were then analyzed. MCS patients had higher theta and alpha and lower delta power when compared to VS/UWS. They showed higher spectral entropy mean value and higher time variability. MCS patients were characterized by spectral entropy fluctuations with periodicities of 70 min (range 57-80 min). Notably, these periodicities closely resemble those described in awake healthy subjects, which were hypothesized to be related to fluctuation in vigilance/attention. No significant periodicity was observed for VS/UWS. The spectral entropy periodicity found in MCS patients could reflect the fluctuation of awareness responsible for the inconsistency of MCS manifestation of cognitively-mediated behaviors. The presence of a 70 min periodicity in spectral entropy could permit clinicians to better choose their time-window when performing a clinical assessment of consciousness. It could also permit to monitor fluctuations in cognitive performance (i.e., response to command) during complementary testing by passive or active electrophysiological or functional neuroimaging paradigms or in resting state conditions.

The goal of our study was to investigate different aspects of sleep, namely the sleep-wake cycle and sleep stages, in the vegetative state/unresponsive wakefulness syndrome (VS/UWS), and minimally conscious state (MCS). A 24-h polysomnography was performed in 20 patients who were in a UWS (n = 10) or in a MCS (n = 10) because of brain injury. The data were first tested for the presence of a sleep-wake cycle, and the observed sleep patterns were compared with standard scoring criteria. Sleep spindles, slow wave sleep, and rapid eye movement sleep were quantified and their clinical value was investigated. According to our results, an electrophysiological sleep-wake cycle was identified in five MCS and three VS/UWS patients. Sleep stages did not always match the standard scoring criteria, which therefore needed to be adapted. Sleep spindles were present more in patients who clinically improved within 6 months. Slow wave sleep was present in eight MCS and three VS/UWS patients but never in the ischemic etiology. Rapid eye movement sleep, and therefore dreaming that is a form of consciousness, was present in all MCS and three VS/UWS patients. In conclusion, the presence of alternating periods of eyes-open/eyes-closed cycles does not necessarily imply preserved electrophysiological sleep architecture in the UWS and MCS, contrary to previous definition. The investigation of sleep is a little studied yet simple and informative way to evaluate the integrity of residual brain function in patients with disorders of consciousness with possible clinical diagnostic and prognostic implications.

(1) Laureys, S., A. M. Owen and N. D. Schiff (2004). "Brain function in coma, vegetative state, and related disorders." Lancet Neurol 3(9): 537-46. (2) Cologan, V., Schabus, M., Ledoux, D., Moonen, G.

The vegetative state (VS) is defined as a condition of wakefulness without awareness. Being awake and being asleep are two behavioral and physiological manifestations of the daily cycles of vigilance and metabolism. International guidelines for the diagnosis of VS propose that a patient fulfills criteria for wakefulness if he/she exhibits cycles of eye closure and eye opening giving the impression of a preserved sleep-wake cycle. We argue that these criteria are insufficient and we suggest guidelines to address wakefulness in a more comprehensive manner in this complex and heterogeneous group of patients. Four factors underlying wakefulness, as well as their interactions, are considered: arousal/ responsiveness, circadian rhythms, sleep cycle, and homeostasis. The first refers to the arousability and capacity to, consciously or not, respond to external stimuli. The second deals with the circadian clock as a synchronizer of physiological functions to environmental cyclic changes. The third evaluates general sleep patterns, while homeostasis refers to the capacity of the body to regulate its internal state and maintain a stable condition. We present examples of reflex responses, activity rhythms, and electroencephalographic (EEG) measurements from patients with disorders of consciousness (DOC) to illustrate these factors of wakefulness. If properly assessed, they would help in the evaluation of consciousness by informing when and in which context the patient is likely to exhibit maximal responsiveness. This evaluation has the potential to improve diagnosis and treatment and may also add prognostic value to the multimodal assessment in DOC.Keywords: disorders of consciousness; wakefulness; circadian rhythms; arousal variability; sleep patterns; homeostasis It could be worst/I could be alone/I could be locked in here on my own. Like a stone that certainly drops/and it never stops/I could be lost or I could be saved. Calling out from beneath the waves. (Crests of waves, Coldplay, 2002) WAKEFULNESSEvery morning most people in this world wake up (Dylan, 1979;Jewel, 1995;Brown, 1970). Waking up is composed of several processes, of which the most obvious is that of regaining consciousness. However, the process of waking up starts well before we regain consciousness, since our internal circadian clock unconsciously times our body rhythms to be prepared for future events. Before the actual time of waking up, both body temperature and some hormone levels (e.g., Cortisol) rise, while other nocturnal variables decrease (e.g., melatonin), thus preparing the arousal system to leave the arms of Morpheus -the god of sleep. But what happens if this highly synchronized process is disrupted by brain injury? Is it possible to "wake up" without regaining consciousness?Wakefulness is a key feature in the diagnosis of disorders of consciousness (DOC), but it is rarely assessed in full and is commonly taken for granted (Multi-Society Task Force on PVS, 1994). The vegetative state (VS) was originally defined as "wakefulness withou...

Consciousness consists of two components: arousal (wakefulness or level of consciousness) and awareness (contents of consciousness) (1). RESULTS CONCLUSIONPreliminary results indicate that the complexity of sleep is higher in MCS than VS patients. Especially, sleep features such as REM sleep, SWS, and sleep spindles as well as cortical desynchronization arousals appear to distinguish between the two clinical entities.It is suggested that this "complexity" of residual sleep patterns reflects more intact thalamo-cortically connected brains. Yet, results are to be interpreted with caution as classical R & K criteria are hard to apply in this DOC population. Especially, the general slowing of EEG frequencies make reliable SWS or spindle detection impossible. We therefore also consider more quantiative sleep analysis as depicted in Fig. 3-4.Overall it is suggested that clinical diagnosis as well as prognosis of DOC patients can be refined using 24hr PSG recordings.