21 Oct Study Identifies Pathway For Retained Awareness In Vegetative State
Medical Research: What is the background for this study? What are the main findings?
Dr. Fernández-Espejo: We have previously shown that a number of patients who appear to be in a vegetative state are actually aware of themselves and their surroundings, and simply unable to show it with their external behavior. In a prior study we demonstrated that a patient who had been repeatedly diagnosed as vegetative state for 12 years was not only fully aware but able to create memories. Notably, this patient was capable to modulate their brain activity in a functional magnetic resonance imaging (fMRI) scanner to answer questions about their condition and preferences for care. In the present study we identified the reason for the dissociation between these patients’ retained awareness and their inability to respond with intentional movement.
First, we used fMRI to demonstrate that a functional connection between the thalamus and the motor cortex is essential for a successful execution of voluntary movements.
Second, we used diffusion tensor tractography, a technique that allows reconstructing and assessing white matter pathways in the brain, to identify damage to such connection (i.e. thalamus and motor cortex) in a paradigmatic patient who produced repeated evidence of covert awareness across multiple examinations, despite clinically appearing as being in a vegetative state.
Medical Research: What should clinicians and patients take away from your report?
Dr. Fernández-Espejo: Clinicians should be aware that lack of responsiveness after severe brain injury should not always be interpreted as a sign of lack of awareness. We suggest that if damage to the connections between thalamus and motor cortex is identified in a patient, the possibility of covert awareness should be considered. These patients would benefit greatly from further specialized neuroimaging assessment to try to identify preserved cognitive function. For patients, these findings may represent a first step towards the development of targeted therapies that, in the future, may help them regain a level of control over their environment.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. Fernández-Espejo: The patients included in this study had suffered a traumatic brain injury. Before our findings can be generalized to a broader population of covertly aware non-responsive patients, further studies need to be conducted in larger groups including patients of different etiologies. This will confirm whether damage to the thalamocortical network involved in motor control is the primary underlying mechanism of this condition.