Boly and colleagues have recently published on Science a paper reporting an event-related potentials (ERP) experiment on vegetative state (VS) patients, minimally conscious state (MSC) patients, and healthy controls. The subjects were given an auditory oddball paradigm. The corresponding ERP patterns were modeled through Dynamic Causal Modeling in order to uncover the effective neural connectivity underlying ERP responses. A model featuring forward and backwards connections between frontal and temporal cortexes was then selected as the best explanatory by means of Bayesian procedures. This model explained very well the electrophysiological activations of healthy subjects and MCs patients. The only effect of being a VS patient relative to the other two groups was the lack of top-down connection between the Inferior Frontal Gyrus (IFG) and the Superior Temporal Gyrus (STG). On the contrary, the connection from STG to IFG was present in all of the three groups. Therefore, the presence or absence of the feedback connection from IFG to STG could be used as a biomarker of consciousness. An established biomarker could make the now notoriously difficult diagnosis of MCS and VS easier. This would in turn make medical decisions about end-of-life issues simpler. In particular a reliable biomarker of consciousness would help tackle objections to withdrawal of treatment. If it is possible to identify MCS and VS patients in a reliable way, then the risk of withdrawing life support to a MCS patient significantly decreases. Therefore, it would become difficult to kill by mistake through withdrawal of life support patients that are in MCS. Furthermore, a biomarker for consciousness can be relevant in legal context too, when compensations for severe brain damage caused by negligence or by criminal acts must be attributed. If validated, this biomarker will become another piece of neuro-evidence that will enter federal courts if able to cope with Daubert standards. It will take time before this and similar experiments find their way into clinical practice and courtrooms, but biomarkers research for mental conditions is proceeding at a fast rate and practical applications are likely to appear in a not-so-remote future.R
Reference
Boly M, Garrido M I, Gosseries O, Bruno M-A, Boveroux P, Schnakers C, Massimini M, Litvak V, Laureys S, and Friston K. 2011. Preserved Feedforward But Impaired Top-Down Processes In The Vegetative State. Science 332: 858-862
DOI: 10.1126/science.1202043
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