A few days ago, we posted in the blog a discussion on consciousness. We gave an overview on the definition of consciousness. While humankind has struggled with this formidable question for millennia, recent developments in neuroscience study, model, and aim to quantify consciousness. It is precisely this last aspect that raised my interest these days, namely how to quantitatively establish a consciousness scale based on EEG. In this context, it is worth mentioning a recent special issue of the journal EEG and Clinical Neuroscience. Such metrics are of enormous interest not only from a philosophical and theoretical point of view, but from a clinical one, given the important consequences that a right diagnosis has in the treatment and care of people with consciousness disorders, e.g. locked-in, coma, vegetative state patients.
The newest published measurement procedure
In the most recent work dealing with this question, a procedure described by Casali and colleagues is based on the application of a TMS pulse to subjects. After this the response of the subjects’ brain is measured with EEG. The measured signals are then represented through a binary two-dimensional map (aka an image) related to the connectivity in the brain. An algorithm that we use daily in our computers for compressing files, i.e. this used for zipping files, is then applied to measure the complexity of the binary map with a unique index denoted as Perturbational Complexity Index (PCI). The more complex the map is, the more conscious the subject. An interesting aspect of the procedure in this paper is that it has been consistently applied to subjects with very different consciousness levels, e.g. anesthetized, in vegetative state, healthy.