Level of consciousness (LOC) is a measurement of a person's arousability and responsiveness to stimuli from the environment. A mildly depressed level of consciousness or alertness may be classed as lethargy; someone in this state can be aroused with little difficulty.
Recent evidence suggests that the quantity and quality of conscious experience may be a function of the complexity of activity in the brain and that consciousness emerges in a critical zone between low and high-entropy states.
Varley et al. proposed fractal shapes as a measure of proximity to this critical point, as fractal dimension encodes information about complexity beyond simple entropy or randomness, and fractal structures are known to emerge in systems nearing a critical point. To validate this, we tested several measures of fractal dimension on the brain activity from healthy volunteers and patients with disorders of consciousness of varying severity. We used a Compact Box Burning algorithm to compute the fractal dimension of cortical functional connectivity networks as well as computing the fractal dimension of the associated adjacency matrices using a 2D box-counting algorithm. To test whether brain activity is fractal in time as well as space, we used the Higuchi temporal fractal dimension on BOLD time-series. We found significant decreases in the fractal dimension between healthy volunteers (n = 15), patients in a minimally conscious state (n = 10), and patients in a vegetative state (n = 8), regardless of the mechanism of injury. We also found significant decreases in adjacency matrix fractal dimension and Higuchi temporal fractal dimension, which correlated with decreasing level of consciousness. These results suggest that cortical functional connectivity networks display fractal character and that this is associated with level of consciousness in a clinically relevant population, with higher fractal dimensions (i.e. more complex) networks being associated with higher levels of consciousness. This supports the hypothesis that level of consciousness and system complexity are positively associated, and is consistent with previous EEG, MEG, and fMRI studies 1).
Although the Reaction Level Scale (RLS) is still used for the assessment of the level of consciousness in distinct centers, its clinical characteristics and significance have been incompletely researched. In the current study, the clinimetric properties, the prognostic value, and the impact of the raters' background on the application of the RLS, in comparison with the Glasgow Coma Scale (GCS), are investigated.
A systematic review of the available clinical evidence for the RLS was first carried out. Next, the RLS was translated into Greek, and patients with neurosurgical pathologies in need of consciousness monitoring were independently assessed with both RLS and GCS, by four raters (two consultants, one resident, and one nurse) within one hour. Interrater reliability, construct validity, and predictive value (mortality and poor outcome, at discharge and at 6 months) were evaluated.
Literature review retrieved 9 clinimetric studies related to the RLS, most of the low quality, indicating that the scale has not been thoroughly studied. Both versions of the RLS (original and modified) showed high interrater reliability (κw >0.80 for all pairs of raters), construct validity (Spearman's p > .90 for all raters), and prognostic value (areas under the curve >0.85 for all raters and outcomes). However, except for broader patients' coverage, it failed to show any advantage over the GCS.
The RLS has not succeeded in showing any advantage over the GCS in terms of reliability and validity. Available evidence cannot justify its use in clinical practice as a substitute to the widely applied GCS 2).