Sondare la coscienza nello stato vegetativo: Il contributo delle neuroimmagini funzionali

Patients in vegetative states (VS) appear to be unaware of themselves and the environment around them, do not engage in intentional behavior and fail to respond to external stimulation. For these reasons, they are considered to be “unconscious”. But, is this really the case? Or, could it be that some patients have been misdiagnosed as unconscious because standard clinical diagnostic tools failed to detect traces of consciousness? In the last decades, advanced neuroimaging techniques, and functional Magnetic Resonance Imaging (fMRI) in particular, have been employed to understand whether the lack of reactivity of VS patients to external stimuli reflects an actual state of unconsciousness, or whether there exists a dissociation between behavioral unresponsiveness and some residual awareness. Results showed that in some patients diagnosed as in VS, brain activations in response to external stimulation were similar to those of healthy individuals. Moreover, some patients were able to actively engage in different mental tasks following instructions, as evidenced by differential brain activations. This shows abilities that are assumed to be incompatible with unconsciousness: preserved language understanding and the ability to perform intentional behavior, bypassing overt motor response. This work describes the contribution of neuroscientific research to better understand the brain mechanisms associated with conscious experience, the so-called neural correlates of consciousness, in VS. Information on the functional state of these neural correlates is crucial to clinical care, as it allows for the implementation of new tools to improve diagnosis and treatment in a very complex clinical population.