A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior

Sounds useful for determining stroke patients consciousness.
An article describing it here;

Brain Shaking Technique - strong magnetic stimulation - Offers Measure of Consciousness

The abstract here; 

http://stm.sciencemag.org/content/5/198/198ra105 

1. Adenauer G. Casali¹,*,^†,
2. Olivia Gosseries²,*,
3. Mario Rosanova¹,
4. Mélanie Boly²,‡,
5. Simone Sarasso¹,
6. Karina R. Casali¹,³,
7. Silvia Casarotto¹,
8. Marie-Aurélie Bruno²,
9. Steven Laureys²,
10. Giulio Tononi⁴ and
11. Marcello Massimini¹,⁵,§

+ Author Affiliations

1. ¹Department of Biomedical and Clinical Sciences ‘Luigi Sacco’, University of Milan, 20157 Milan, Italy.
2. ²Coma Science Group, Cyclotron Research Centre and Neurology Department, University and University Hospital of Liège, 4000 Liège, Belgium.
3. ³Institute of Science and Technology, Federal University of São Paulo, 12231-280 São José dos Campos, Brazil.
4. ⁴Department of Psychiatry, University of Wisconsin, Madison, WI 53719, USA.
5. ⁵Istituto Di Ricovero e Cura a Carattere Scientifico, Fondazione Don Carlo Gnocchi, 20148 Milan, Italy.

+ Author Notes

• ↵* These authors contributed equally to this work.
• ↵† Present address: Faculty of Medicine Clinics Hospital, University of São Paulo, 05403-000 São Paulo, Brazil.
• ↵‡ Present address: Department of Psychiatry, University of Wisconsin, Madison, WI 53719, USA.

1. ↵§Corresponding author. E-mail: marcello.massimini@unimi.it

Abstract

One challenging aspect of the clinical assessment of brain-injured, unresponsive patients is the lack of an objective measure of consciousness that is independent of the subject’s ability to interact with the external environment. Theoretical considerations suggest that consciousness depends on the brain’s ability to support complex activity patterns that are, at once, distributed among interacting cortical areas (integrated) and differentiated in space and time (information-rich). We introduce and test a theory-driven index of the level of consciousness called the perturbational complexity index (PCI). PCI is calculated by (i) perturbing the cortex with transcranial magnetic stimulation (TMS) to engage distributed interactions in the brain (integration) and (ii) compressing the spatiotemporal pattern of these electrocortical responses to measure their algorithmic complexity (information). We test PCI on a large data set of TMS-evoked potentials recorded in healthy subjects during wakefulness, dreaming, nonrapid eye movement sleep, and different levels of sedation induced by anesthetic agents (midazolam, xenon, and propofol), as well as in patients who had emerged from coma (vegetative state, minimally conscious state, and locked-in syndrome). PCI reliably discriminated the level of consciousness in single individuals during wakefulness, sleep, and anesthesia, as well as in patients who had emerged from coma and recovered a minimal level of consciousness. PCI can potentially be used for objective determination of the level of consciousness at the bedside.